Echinococcus granulosus and E. multilocularis are causative agents of hydatid cysts
Echinococcus granulosus
Epidemiology
The organism is common in Asia, Australia, Eastern Africa, southern Spain, southern parts of South America and northern parts of North America. The incidence of human infection about 1 to 2 per 1000 population and may be higher in rural areas of affected regions.
Morphology
This is the smallest of all tapeworms (3 to 9 mm long) with only 3 proglottids.
Life cycle
The adult worm lives in domestic and wild carnivorous animals. Eggs, passed by infected animals, are ingested by the grazing farm animals or man, localize in different organs and develop into hydatid cysts containing many larvae (proto-scolices or hydatid sand) (Figure 8). When other animals consume infected organs of these animals, proto-scolices escape the cyst, enter the small intestine and develop into adult worms (Figure 7). Echinococcus eggs, when swallowed by man, produce embryos that penetrate the small intestine, enter the circulation and form cysts in liver, lung, bones, and sometimes, brain. The cyst is round and measures 1 to 7 cm in diameter, although it may grow to be 30 cm. The cyst consists of an outer anuclear hyaline cuticula and an inner nucleated germinal layer containing clear yellow fluid. Daughter cysts attach to the germinal layer, although some cysts, known as brood cysts, may have only larvae (hydatid sand). Man is a dead end host.
Symptoms
The symptoms, comparable to those of a slowly growing tumor, depend upon the location of the cyst. Large abdominal cysts produce increasing discomfort. Liver cysts cause obstructive jaundice. Peribronchial cysts may produce pulmonary abscesses. Brain cysts produce intracranial pressure and Jacksonian epilepsy. Kidney cysts cause renal dysfunction. The contents of a cyst may produce anaphylactic responses.
Diagnosis
Clinical symptoms of a slow-growing tumor accompanied by eosinophilia are suggestive. Intradermal (Casoni) test with hydatid fluid is useful. Pulmonary cysts and calcified cysts can be visualized using x-rays. Antibodies against hydatid fluid antigens have been detected in a sizable population of infected individuals by ELISA or indirect hemagglutination test.
Treatment and control
Treatment involves surgical removal of cyst or inactivation of hydatid sand by injecting the cyst with 10% formalin and its removal within five minutes. It has been claimed that a high dose of Mebendazole results in some success. Preventive measures involve avoiding contact with infected dogs and cats and elimination of their infection
Sabtu, 09 Februari 2008
COCCIDIAL PARASITES
Coccidia in the genera Cryptosporidium, Eimeria, Isospora, arcocystis, and Toxoplasma are the most economically important group of protozoans in domestic animals in the United States. Historically the structure of the sporulated oocyst, especially the number of sporocysts and sporozoites, was used as a major characteristic to differentiate genera of coccidia.
Eimeria and isospora
· A. Host specificity - these parasities have a narrow host range -(stenoxenous).
· B. Organ specificity - these parasities are usually found in a specific organ.
· C. Site specificity within organ or cell - these parasities inhabit specific sites within an organ or cell.
· D. Monoxenous - coccidia usually parasitize one host, the definitive host.
· E. Reproduction
o 1. Schizogony (Merogony) -multiple fission.
o 2. Gamogony (syngamy) - union of similar gametes (Isogamy)
· F. Structure of sporulated oocyst
o 1. Eimeria - 4 sporocysts, each with 2 sporozoites
o 2. Isospora - 2 sporocysts, each with 4 sporozoites
Detailed Life Cycle of The Coccida Eimeria and Isospora
Infection of the definitive host begins with the ingestion of infective oocysts containing fully developed sporozoites (within sporocysts) which are freed in the lumen of the intestine by enzymic action of digestion upon the oocyst wall. The freed motile sporozoites penetrate epithelial cells of the intestine and round-up to form trophozoites which undergo a form of internal budding or cell division which is termed a schizont at this point (or schizogony the process). The later process (first generation schizonts) is terminated when the round internal cells elongate or become sickle shaped (which are termed merozoites, first generation) and are released (rupture host cells) into the intestinal lumen to enter other cells in their vicinity and repeating a second and/maybe a third generation of schiogony (merogony). Most merozoites of the second generation form macrogamethocytes with macrogametes which undergo no cell division. Those merozoites which develop into microgametocytes undergo further division forming biflagellated microgametes. The later leave host cells to penetrate other cells containing macrogametes resulting in fertilization, forming the zygote. The latter lays down a wall around itself from the eosinophilic plastic granules in its cytoplasm, thus forming the oocysts which breaks out of the host cells to be passed in the feces to sporulate or become infective in about 2-3 days under ideal conditions of temperature (Sporogony).
Eimeria and isospora
· A. Host specificity - these parasities have a narrow host range -(stenoxenous).
· B. Organ specificity - these parasities are usually found in a specific organ.
· C. Site specificity within organ or cell - these parasities inhabit specific sites within an organ or cell.
· D. Monoxenous - coccidia usually parasitize one host, the definitive host.
· E. Reproduction
o 1. Schizogony (Merogony) -multiple fission.
o 2. Gamogony (syngamy) - union of similar gametes (Isogamy)
· F. Structure of sporulated oocyst
o 1. Eimeria - 4 sporocysts, each with 2 sporozoites
o 2. Isospora - 2 sporocysts, each with 4 sporozoites
Detailed Life Cycle of The Coccida Eimeria and Isospora
Infection of the definitive host begins with the ingestion of infective oocysts containing fully developed sporozoites (within sporocysts) which are freed in the lumen of the intestine by enzymic action of digestion upon the oocyst wall. The freed motile sporozoites penetrate epithelial cells of the intestine and round-up to form trophozoites which undergo a form of internal budding or cell division which is termed a schizont at this point (or schizogony the process). The later process (first generation schizonts) is terminated when the round internal cells elongate or become sickle shaped (which are termed merozoites, first generation) and are released (rupture host cells) into the intestinal lumen to enter other cells in their vicinity and repeating a second and/maybe a third generation of schiogony (merogony). Most merozoites of the second generation form macrogamethocytes with macrogametes which undergo no cell division. Those merozoites which develop into microgametocytes undergo further division forming biflagellated microgametes. The later leave host cells to penetrate other cells containing macrogametes resulting in fertilization, forming the zygote. The latter lays down a wall around itself from the eosinophilic plastic granules in its cytoplasm, thus forming the oocysts which breaks out of the host cells to be passed in the feces to sporulate or become infective in about 2-3 days under ideal conditions of temperature (Sporogony).
Medically Important Protozoa
Protozoa means "first animal" and refers to simple eukaryotic organisms composed of a single cell (e.g. amoebae). Reproduction may be through simple cell division (e.g. the ameboflagellates) or sexual involving the fusion of gametes in part of the life cycle (e.g. the apicomplexa) as described below. Some protozoa can form a protective cyst stage capable of withstanding harsh environmental conditions.
Ameboflagellates
These use pseudopodia or flagella for locomotion.
Amoebae. These are characterized by a feeding and dividing trophozoite stage that can form a temporary resistant cyst stage.
Entamoeba histolytica is the cause of amoebic dysentery producing severe infection of the intestines that can spread to the liver. The organism is characterized by a trophozoite and cyst stage. E. histolytica is an example of a true parasite in that the organism cannot multiply outside of the host. Other amoebae occur naturally in soil and water environments which is their preferred habitat for feeding and replication. These amoebae are termed "free-living" as they have no natural host in which parasitism occurs. They can infect man opportunistically producing severe and often fatal disease. Such free-living amoebae are the Acanthameba, Naegleria fowleri and Balamuthia mandrillaris, all of which can infect the central nervous system. In addition, Acanthameba species can also invade the eye.
Flagellates
These organisms have flagella in the trophozoite stage. Trichomonas vaginalis is a common sexually transmitted organism causing trichomoniasis infection of the vagina and urethra. Giardia lamblia causes giardiasis producing symptoms of diarrhea and other intestinal disturbances. Infection arises from the ingestion of cysts, usually through contaminated water.
Trypanosoma brucei gambiense and T. brucei rhodesiense cause trypanosomiasis, more commonly known as African sleeping sickness. The disease is an arthropod (insect)-borne infections and is spread by the bite of the tsetse fly in which part of the trypanosome life cycle is completed. The eventual invasion of the central nervous system by the trypanosomes gives rise a comatosed state from which the common name for the disease is derived.
Trypanosoma cruzi causes Chagas' disease (American trypanosomiasis). The intermediate host in this case are triatomid bugs that feed off the blood of man. Infection results from the inoculation of the bug's feces that contains the organism into the bite wound. Individuals who survive the acute stage of the disease are frequently left with chronic and progressive neuronal and smooth muscle lesions in the heart and gastrointestinal tract. T. cruzi has an extensive reservoir in wild and domestic mammals and therefore Chagas' disease is a zoonosis.
Ameboflagellates
These use pseudopodia or flagella for locomotion.
Amoebae. These are characterized by a feeding and dividing trophozoite stage that can form a temporary resistant cyst stage.
Entamoeba histolytica is the cause of amoebic dysentery producing severe infection of the intestines that can spread to the liver. The organism is characterized by a trophozoite and cyst stage. E. histolytica is an example of a true parasite in that the organism cannot multiply outside of the host. Other amoebae occur naturally in soil and water environments which is their preferred habitat for feeding and replication. These amoebae are termed "free-living" as they have no natural host in which parasitism occurs. They can infect man opportunistically producing severe and often fatal disease. Such free-living amoebae are the Acanthameba, Naegleria fowleri and Balamuthia mandrillaris, all of which can infect the central nervous system. In addition, Acanthameba species can also invade the eye.
Flagellates
These organisms have flagella in the trophozoite stage. Trichomonas vaginalis is a common sexually transmitted organism causing trichomoniasis infection of the vagina and urethra. Giardia lamblia causes giardiasis producing symptoms of diarrhea and other intestinal disturbances. Infection arises from the ingestion of cysts, usually through contaminated water.
Trypanosoma brucei gambiense and T. brucei rhodesiense cause trypanosomiasis, more commonly known as African sleeping sickness. The disease is an arthropod (insect)-borne infections and is spread by the bite of the tsetse fly in which part of the trypanosome life cycle is completed. The eventual invasion of the central nervous system by the trypanosomes gives rise a comatosed state from which the common name for the disease is derived.
Trypanosoma cruzi causes Chagas' disease (American trypanosomiasis). The intermediate host in this case are triatomid bugs that feed off the blood of man. Infection results from the inoculation of the bug's feces that contains the organism into the bite wound. Individuals who survive the acute stage of the disease are frequently left with chronic and progressive neuronal and smooth muscle lesions in the heart and gastrointestinal tract. T. cruzi has an extensive reservoir in wild and domestic mammals and therefore Chagas' disease is a zoonosis.
Snail-Mediated Helminthiases
This important group of snail-transmitted helminthiases is all caused by trematodes (flukes) that undergo a complicated cycle involving various species of land or aquatic snails. The most significant of these fluke infections is schistosomiasis and over 200 million people are estimated to be infected world-wide. The three common species infecting man, Schistosoma mansoni, S. japonicum and S. haematobium have similar life cycles. Eggs are passed in the urine (S. haematobium) or feces (Schistosoma mansoni and S. japonicum) and hatch in natural waters. Miracidia hatch from the eggs, penetrate suitable snails and develop two generations of sporocysts. The last of these then produces fork-tailed cercariae. These cercariae penetrate the skin when a new host comes into contact with the contaminated water. Once through the skin the cercariae shed their tails and become schistosomulae that then migrate through the tissues to the liver. Here male and female flukes copulate and migrate to either the bladder or rectum where eggs are laid. Schistosomiasis can result in chronic liver, spleen and bladder damage.
Fascioliasis. Fasciola hepatica is found in most herbivores (but primarily sheep) that graze in wet pasturage where the intermediate host, snails of the genus Lymnaea, are found. F. hepatica eggs, shed from the infected primary host, mature into the embryonated form in the environment. These then hatch and release a motile miracidia that seeks out and penetrates the tissue of the intermediate snail host. Cercaria are produced in the snail that when released into the environment can encyst to produce metacercariae. In temperate climates man is often infected by eating wild watercress on which metacercariae have collected. After being ingested, the metacercariae pass through the duodenal wall and penetrate the liver capsule. Following maturation of the young flukes, the adults finally come to lie in the bile ducts or adjacent liver tissue. Here they cause severe damage to the biliary tract and eggs are passed with the bile into the feces to continue the cycle.
Fascioliasis. Fasciola hepatica is found in most herbivores (but primarily sheep) that graze in wet pasturage where the intermediate host, snails of the genus Lymnaea, are found. F. hepatica eggs, shed from the infected primary host, mature into the embryonated form in the environment. These then hatch and release a motile miracidia that seeks out and penetrates the tissue of the intermediate snail host. Cercaria are produced in the snail that when released into the environment can encyst to produce metacercariae. In temperate climates man is often infected by eating wild watercress on which metacercariae have collected. After being ingested, the metacercariae pass through the duodenal wall and penetrate the liver capsule. Following maturation of the young flukes, the adults finally come to lie in the bile ducts or adjacent liver tissue. Here they cause severe damage to the biliary tract and eggs are passed with the bile into the feces to continue the cycle.
Soil-Mediated Helminthiases
Soil-transmitted helminthic infections are of two types: the hookworms, which undergo a cycle of development in the soil (the larvae being infective), and a group of nematodes that survive in the soil merely as eggs that have to be ingested in order for the cycle to continue.
Hookworms. The most common hookworms are Ancylostoma duodenale and Necator americanus. Adults attach to the walls of the jejunum and females lay large numbers of eggs that are passed out with the feces. The eggs hatch in the soil and infect man by usually burrowing through the soles of the feet. The larvae then migrate to infect the heart and lungs before passing into the tracheae, pharynx and then the small intestine.
Strongyloides stercoralis. Females live in the mucosal glands of the small intestine. Eggs hatch in these glands and the larvae are passed with the feces into the soil. As with other hookworms, infection results from the larvae burrowing into the skin. The rest of the life cycle is as for A. duodenale and N. americanus.
Ascariasis. Adult worms of Ascaris lumbricoides live in the small intestine where they lay large numbers of eggs that are passed out with the feces. Unlike the hookworms, the eggs are the infectious form in which the larvae develop. When ingested, the eggs hatch in the jejunum, penetrate the mucosa and are carried through the hepatic circulation to the heart and lungs. They again enter the stomach via the tracheae and oesophagus before growing to adulthood in the small intestine. Pneumonitis and intestinal obstruction may accompany heavy infestations.
Toxocariasis. The disease results from the accidental infection of man with eggs of the ascarid roundworm of the dog, Toxocara canis, and cat, T. cati. The life cycle is the same as that of Ascaris but the invasive larvae become arrested in various tissues where they are phagocytosed. In the process they induce marked eosinophilia and local tissue reaction commonly involving the liver and eye.
Trichurias. Trichuris trichiura ("whipworm") inhabits the caecum where they attach to the mucosa. Eggs from the mature worms are passed with the feces and develop in the soil. When swallowed, the eggs hatch in the small intestine and the developing larvae pass directly to their attachment sites in the large intestine. Heavy infections can cause abdominal pain and chronic bloody diarrhea that may result in rectal prolapse.
Hookworms. The most common hookworms are Ancylostoma duodenale and Necator americanus. Adults attach to the walls of the jejunum and females lay large numbers of eggs that are passed out with the feces. The eggs hatch in the soil and infect man by usually burrowing through the soles of the feet. The larvae then migrate to infect the heart and lungs before passing into the tracheae, pharynx and then the small intestine.
Strongyloides stercoralis. Females live in the mucosal glands of the small intestine. Eggs hatch in these glands and the larvae are passed with the feces into the soil. As with other hookworms, infection results from the larvae burrowing into the skin. The rest of the life cycle is as for A. duodenale and N. americanus.
Ascariasis. Adult worms of Ascaris lumbricoides live in the small intestine where they lay large numbers of eggs that are passed out with the feces. Unlike the hookworms, the eggs are the infectious form in which the larvae develop. When ingested, the eggs hatch in the jejunum, penetrate the mucosa and are carried through the hepatic circulation to the heart and lungs. They again enter the stomach via the tracheae and oesophagus before growing to adulthood in the small intestine. Pneumonitis and intestinal obstruction may accompany heavy infestations.
Toxocariasis. The disease results from the accidental infection of man with eggs of the ascarid roundworm of the dog, Toxocara canis, and cat, T. cati. The life cycle is the same as that of Ascaris but the invasive larvae become arrested in various tissues where they are phagocytosed. In the process they induce marked eosinophilia and local tissue reaction commonly involving the liver and eye.
Trichurias. Trichuris trichiura ("whipworm") inhabits the caecum where they attach to the mucosa. Eggs from the mature worms are passed with the feces and develop in the soil. When swallowed, the eggs hatch in the small intestine and the developing larvae pass directly to their attachment sites in the large intestine. Heavy infections can cause abdominal pain and chronic bloody diarrhea that may result in rectal prolapse.
Genus ostertagia pada ruminat
Cacing ini merupakan cacing lambung coklat atau cacing lambung berukuran sedang pada ruminansia. Kepala dan kapsula bukal kecil. Terdapat papila-papila servikal. Spikulum pendek, sama panjang, dan berakhir pada 2 atau 3 tonjolan. Terdapat sebuah gubernakulum. Vulva terletak pada 1/5 bagian posterior tubuh, dan kadang-kadang tertutup oleh cuping kutikuler. Siklus hidupnya mirip dengan siklus Trichostrongylus.
Ostertagia ostertagi terdapat pada abomasum sapi, domba dan ruminansia lain. Cacing ini berwarna coklat kemerahan. Panjang yang jantan 6-8 mm dengan spikulum 220-230 mikron berakhir pada tiga tonjolan tumpul berkait; gubernakulum dengan panjang 65 mikron. Bnetinanya 8-10 mm dengan telur berukuran 74-90 x 38-44 mikron.
Ostertagia lyrata merupakan cacing abomasum lain pada sapi yang juga ditemukan pada domba dan berbagai ruminansia liar. Yang jantan mencapai sekitar 9 mm dengan spikulum sekitar 230 mikron dan gubernakulum sekitar 63 mikron. Cacing betina mencapai panjang 9 mm dengan telur 75-85 x 34-42 mikron.
Ostertagia circumcincta terdapat pada abomasum domba dan ruminansia lain (tidak pada sapi) di seluruh dunia, dan merupakan ostertagia yang paling penting pada domba. Yang jantan 7-9 mm, dengan spikulum 280-320 mikron dan gubernakulum 90 mikron. Cacing betina 10-12 mm, dengan telur 85-103 x 44-58 mikron.
Ostertagia ostertagi terdapat pada abomasum sapi, domba dan ruminansia lain. Cacing ini berwarna coklat kemerahan. Panjang yang jantan 6-8 mm dengan spikulum 220-230 mikron berakhir pada tiga tonjolan tumpul berkait; gubernakulum dengan panjang 65 mikron. Bnetinanya 8-10 mm dengan telur berukuran 74-90 x 38-44 mikron.
Ostertagia lyrata merupakan cacing abomasum lain pada sapi yang juga ditemukan pada domba dan berbagai ruminansia liar. Yang jantan mencapai sekitar 9 mm dengan spikulum sekitar 230 mikron dan gubernakulum sekitar 63 mikron. Cacing betina mencapai panjang 9 mm dengan telur 75-85 x 34-42 mikron.
Ostertagia circumcincta terdapat pada abomasum domba dan ruminansia lain (tidak pada sapi) di seluruh dunia, dan merupakan ostertagia yang paling penting pada domba. Yang jantan 7-9 mm, dengan spikulum 280-320 mikron dan gubernakulum 90 mikron. Cacing betina 10-12 mm, dengan telur 85-103 x 44-58 mikron.
Heterakis gallinarum
Ciri-ciri : Cacing jantan panjangnya 4-13 mm, dan diameter 120-470 mikron dengan alat penghisap preanal berdiameter 38-114 mikron, spikulum kanan panjangnya 0,85-2,80 mm dan spikulum kiri 0,37-1,10 mm. Cacing betina 8-15 mm, dengan telur berbentuk elips, berdinding tebal berukuran 63-75 x 36-48 mikron.
Diphyllobothrium latum (fish or broad tapeworm)
Epidemiology
Fish tapeworm infection is distributed worldwide, in the subarctic and temperate regions; it is associated with eating of raw or improperly cooked fresh water fish.
Morphology
This is the longest tapeworm found in man, ranging from 3-10 meters with more than 3000 proglottids. The scolex resembles two almond-shaped leaves and the proglottids are broader than they are long, a morphology reflected in the organism's name. Eggs are 30 x 50 micrometers in size and contain an embryo with 3 pairs of hooklets (figure 4).
Life cycle
Man and other animals are infected by eating uncooked fish that contains plerocercoid larvae (15 x 2 mm) which attach to the small intestinal wall and mature into adult worms in 3 to 5 weeks. Eggs discharged from gravid proglottids in the small intestine are passed in the feces. The egg hatches in fresh water to produce a ciliated coracidium which needs to be ingested by a water flea (Cyclops) where it develops into a procercoid larva. When infected Cyclops are ingested by the freshwater fish, the procercoid larva penetrates the intestinal wall and develops into a plerocercoid larva, infectious to man (figure 3).
Symptoms
Clinical symptoms may be mild, depending on the number of worms. They include abdominal discomfort, loss of weight, loss of appetite and some malnutrition. Anemia and neurological problems associated with vitamin B12 deficiency are seen in heavily infected individuals.
Diagnosis
Diagnosis is based on finding many typical eggs and empty proglottids in feces (Figure 3). A history of raw fish consumption and residence in an endemic locality is helpful.
Treatment and control
Praziquantel is the drug of choice. Freezing for 24 hours, thorough cooking or pickling of fish kills the larvae. Fish reservoirs should be kept free of raw sewage.
Fish tapeworm infection is distributed worldwide, in the subarctic and temperate regions; it is associated with eating of raw or improperly cooked fresh water fish.
Morphology
This is the longest tapeworm found in man, ranging from 3-10 meters with more than 3000 proglottids. The scolex resembles two almond-shaped leaves and the proglottids are broader than they are long, a morphology reflected in the organism's name. Eggs are 30 x 50 micrometers in size and contain an embryo with 3 pairs of hooklets (figure 4).
Life cycle
Man and other animals are infected by eating uncooked fish that contains plerocercoid larvae (15 x 2 mm) which attach to the small intestinal wall and mature into adult worms in 3 to 5 weeks. Eggs discharged from gravid proglottids in the small intestine are passed in the feces. The egg hatches in fresh water to produce a ciliated coracidium which needs to be ingested by a water flea (Cyclops) where it develops into a procercoid larva. When infected Cyclops are ingested by the freshwater fish, the procercoid larva penetrates the intestinal wall and develops into a plerocercoid larva, infectious to man (figure 3).
Symptoms
Clinical symptoms may be mild, depending on the number of worms. They include abdominal discomfort, loss of weight, loss of appetite and some malnutrition. Anemia and neurological problems associated with vitamin B12 deficiency are seen in heavily infected individuals.
Diagnosis
Diagnosis is based on finding many typical eggs and empty proglottids in feces (Figure 3). A history of raw fish consumption and residence in an endemic locality is helpful.
Treatment and control
Praziquantel is the drug of choice. Freezing for 24 hours, thorough cooking or pickling of fish kills the larvae. Fish reservoirs should be kept free of raw sewage.
Helminth infections acquired through the gastrointestinal tract
Trichinosis. Trichinella spiralis is the cause of trichinosis in man. The nematode circulates between rats and pigs with man becoming infected from eating raw or inadequately cooked pork products. Encysted larvae in the meat excyst (hatch) in the intestine and develop into minute adults in the mucosa. These mature and the females deposit larvae that then migrate through the tissues to reach skeletal muscles in which they encyst. Human infections may be asymptomatic but can include fever, orbital oedema, myalgia and eosinophilia. In the extreme, infection can be fatal through myocarditis or encephalitis.
Enterobiasis. Enterobias vermicularis is a small thread-like "pinworm" mainly infecting young children. The female emerges to the perianal region usually at night and lays some 10,000-15,000 eggs and then dies. In the process they cause severe pruritis (itching). The embryonated eggs are infectious on ingestion and hatch in the duodenum. The larvae pass to the caecum where they mature into adults. Because of the pruritis, children often re-infect themselves from eggs under their fingernails. Bedding is also a source of infection and can be a means of spreading the organism in families and institutions such as orphanages and boarding schools.
Taenia solium (pork tapeworm). The adult lives in the small intestine of man that is the definitive host. Segments of the worm pass through the anus and release large numbers of eggs that can survive for long periods outside of the body. When ingested by pigs, the eggs hatch and each releases an onchosphere that migrates through the intestinal wall and blood vessels to reach striated muscle where encystment occurs. When inadequately cooked pig meat is eaten by man, excystment occurs in the small intestine and an adult cestode (worm) develops. If the eggs are released into the upper intestine of man (e.g. through regurgitation) they can invade the host setting up a potentially dangerous larval infection known as cysticercosis in muscle and other sites.
Taenia saginata (beef tapeworm). This also infects man through cattle. The life cycle is similar to T. solium and in both species the adult tapeworm can grow up to 10 meters in length.
Hydatidosis. This is caused by the tapeworm Echinococcus granulosus. The adult worm inhabits the small intestine of dogs from which the eggs of the species are passed. These eggs can be ingested by herbivorous animals and hatch in the duodenum. The embryos enter the circulation where they are carried to various sites to develop into cysts. Dogs become infected when they eat contaminated offal. Humans are infected if they accidentally ingest eggs from infected dogs and the liver is the most common site of infection in which hydatid cysts form.
References: Baker, J.R. and Muller, R (Eds). Advances in Parasitology. Academic Press, London. Knight, R. (1982). Parasites Diseases in Man. Churchill Livingstone, London. Peters, W. and Gilles, H.M. (1995) Colour Atlas of Tropical Medicine and Parasitology. Mosby-Wolfe.
Enterobiasis. Enterobias vermicularis is a small thread-like "pinworm" mainly infecting young children. The female emerges to the perianal region usually at night and lays some 10,000-15,000 eggs and then dies. In the process they cause severe pruritis (itching). The embryonated eggs are infectious on ingestion and hatch in the duodenum. The larvae pass to the caecum where they mature into adults. Because of the pruritis, children often re-infect themselves from eggs under their fingernails. Bedding is also a source of infection and can be a means of spreading the organism in families and institutions such as orphanages and boarding schools.
Taenia solium (pork tapeworm). The adult lives in the small intestine of man that is the definitive host. Segments of the worm pass through the anus and release large numbers of eggs that can survive for long periods outside of the body. When ingested by pigs, the eggs hatch and each releases an onchosphere that migrates through the intestinal wall and blood vessels to reach striated muscle where encystment occurs. When inadequately cooked pig meat is eaten by man, excystment occurs in the small intestine and an adult cestode (worm) develops. If the eggs are released into the upper intestine of man (e.g. through regurgitation) they can invade the host setting up a potentially dangerous larval infection known as cysticercosis in muscle and other sites.
Taenia saginata (beef tapeworm). This also infects man through cattle. The life cycle is similar to T. solium and in both species the adult tapeworm can grow up to 10 meters in length.
Hydatidosis. This is caused by the tapeworm Echinococcus granulosus. The adult worm inhabits the small intestine of dogs from which the eggs of the species are passed. These eggs can be ingested by herbivorous animals and hatch in the duodenum. The embryos enter the circulation where they are carried to various sites to develop into cysts. Dogs become infected when they eat contaminated offal. Humans are infected if they accidentally ingest eggs from infected dogs and the liver is the most common site of infection in which hydatid cysts form.
References: Baker, J.R. and Muller, R (Eds). Advances in Parasitology. Academic Press, London. Knight, R. (1982). Parasites Diseases in Man. Churchill Livingstone, London. Peters, W. and Gilles, H.M. (1995) Colour Atlas of Tropical Medicine and Parasitology. Mosby-Wolfe.
TOXOPLASMA GONDII
Classification
1. Toxoplasma gondii is placed in the phylum Apicomplexa
2. Invasive stages have typical apical complex
3. Part of life cycle in cats and other felids is similar to Eimeria and Isosopora
4. Toxon = arc; Plastos = form. One stage in the life cycle is arc- shaped.
5. The species name is derived from the host in which the parasites was first described: Ctenodactylus gundi = small African rodent.
Geographagic Distribution: worldwide
Epidemiology and Hosts
· 1. 500 million people worldwide have antibody to T. gondii
· 2. Prevalenc is the same in men and women
· 3. Prevalence of T. gondii in other animals.
o a. Sheep -20%
o b. Cattle - 25%
o c. Pigs - 30%
o d. Dogs - 30%
o e. Cats - 45%
o f. Birds - 12%
o g. Toxoplasma gondii infects many species of warm-blooded vertebrates (euryxenous)
· 4. Modes of transmission:
o a. Feline feces containing infective oocyst
o b. Eating raw of undercooked meat
o c. Congenital and acquired toxoplasmosis
Toxoplasma is transmitted to cats that ingest either sporulated oocysts or tissues infected with tachyzoites, but the most common source of infection is ingestion of tissues containing cysts. On ingestion of cysts, bracyzoites released in the gastrointestinal tract initiate an enteroepithelial cycle of asexual and sexual multiplication, followed by oocyst development and shedding of unsporulated oocysts with feces. An extraintestinal cycle, like that seen in nonfelids, also occurs in cats
Life cycle
The coccidium Toxoplasma gondii infects all warm-blooded animals, including humans. Felids (both domestic and wild) are the only definitive hosts; felids and nonfelids are intermediate hosts. Toxoplasma can betransmitted to intermediate hosts via oocysts in feline feces, via cysts in host tissues (meat), and via techyzoites transplacentally. Unsporulated oocysts in feline feces sporulate outside the body and become infectious. On ingestion, sporozoites excyst and multiply in the intestine and associated lymph nodes as tachyzoites. Tachyzoites multiply by endodyogeny (see Figure 2.30) for numerous generations, spreading through tissues and circulation, and then encyst. Cysts persist most frequently in the brain, liver, muscles, and retina. They are usually spherical or elongate, thin-walled structures containing a few to several hundred slender PAS-positive bradyzoites or slowly multiplying zoites. Cysts ingested by a nonfeline host release bradyzoites, which become tachyzoitesm, and the cycle is repeated. Infection by either oocysts or cysts during pregnancy can result in transplacental infection of the fetus with tachyzoites.
Pathology
Trachyzoite multiplication results in focal necrosis, the most characteristic lesion of toxoplasmosis. Inflammation usually follows necrosis. Pneumonitis is the predominant lesion in fatal toxoplasmosis in cats and dogs; placental necrosis with white flecks or multiple white, chalky, necrotic nodules and associated abortion predominate in sheep and goats. Histologcially, this necrosis is confined to the cotyledons where individual and small group of tachyzoites are often difficult to recognize among degenerating host cells. Encephalomyelitis is the predominant lesion in sheep.
Diagnosis
Diagnosis of Toxoplasma is performed at postmortem by identification of organisms in infected tissue. Diagnosis in live animals is aided by serologic tests and by bioassay or xenodiagnosis in mice.
Prevention and Control
The following preventative measures apply to all persons, but because toxoplasmosis is most severe in the perintatal period, they should be emphasized for pregnant women and for young children.
· 1. Avoid contamination with oocysts from cat feces by:
o a. Feeding cats dry, canned or thorougly cooked food
o b. Preventing cats from hunting birds and rodents
o c. Emptying litter boxes daily, before oocysts sporulate
o d. Wearing gloves or thoroughly washing hands after working in the garden or with soil, and before eating or touching the face
o e. Covering children’s sandboxes when not in use
o f. Preventing aerosols in the laboratory during centrifugation of potentially infected biological samples
o g. Boiling drinking water from streams, ponds, or lakes frequented by cats
· 2. Avoid ingestion of tissue cysts by cooking meat to over 660 C and washing hands after handling raw meat.
The following preventative measures apply to farms and other animal-rearing facilities. Avoid contamination of feed or water with oocysts in cat feces by:
· 1. Using rodenticides and traps to prevent cats from hunting rodents
· 2. covering, closing or locking feed-storage facilities to prevent cats from entering and defecating
· 3. Promptly removing cat feces from building stalls or cages; and flushing, burning, or burying them to destroy oocysts
· 4. Providing adequate dry, canned, or thoroughly cooked food and separate water to prevent cats from sharing facilities used by other animals.
1. Toxoplasma gondii is placed in the phylum Apicomplexa
2. Invasive stages have typical apical complex
3. Part of life cycle in cats and other felids is similar to Eimeria and Isosopora
4. Toxon = arc; Plastos = form. One stage in the life cycle is arc- shaped.
5. The species name is derived from the host in which the parasites was first described: Ctenodactylus gundi = small African rodent.
Geographagic Distribution: worldwide
Epidemiology and Hosts
· 1. 500 million people worldwide have antibody to T. gondii
· 2. Prevalenc is the same in men and women
· 3. Prevalence of T. gondii in other animals.
o a. Sheep -20%
o b. Cattle - 25%
o c. Pigs - 30%
o d. Dogs - 30%
o e. Cats - 45%
o f. Birds - 12%
o g. Toxoplasma gondii infects many species of warm-blooded vertebrates (euryxenous)
· 4. Modes of transmission:
o a. Feline feces containing infective oocyst
o b. Eating raw of undercooked meat
o c. Congenital and acquired toxoplasmosis
Toxoplasma is transmitted to cats that ingest either sporulated oocysts or tissues infected with tachyzoites, but the most common source of infection is ingestion of tissues containing cysts. On ingestion of cysts, bracyzoites released in the gastrointestinal tract initiate an enteroepithelial cycle of asexual and sexual multiplication, followed by oocyst development and shedding of unsporulated oocysts with feces. An extraintestinal cycle, like that seen in nonfelids, also occurs in cats
Life cycle
The coccidium Toxoplasma gondii infects all warm-blooded animals, including humans. Felids (both domestic and wild) are the only definitive hosts; felids and nonfelids are intermediate hosts. Toxoplasma can betransmitted to intermediate hosts via oocysts in feline feces, via cysts in host tissues (meat), and via techyzoites transplacentally. Unsporulated oocysts in feline feces sporulate outside the body and become infectious. On ingestion, sporozoites excyst and multiply in the intestine and associated lymph nodes as tachyzoites. Tachyzoites multiply by endodyogeny (see Figure 2.30) for numerous generations, spreading through tissues and circulation, and then encyst. Cysts persist most frequently in the brain, liver, muscles, and retina. They are usually spherical or elongate, thin-walled structures containing a few to several hundred slender PAS-positive bradyzoites or slowly multiplying zoites. Cysts ingested by a nonfeline host release bradyzoites, which become tachyzoitesm, and the cycle is repeated. Infection by either oocysts or cysts during pregnancy can result in transplacental infection of the fetus with tachyzoites.
Pathology
Trachyzoite multiplication results in focal necrosis, the most characteristic lesion of toxoplasmosis. Inflammation usually follows necrosis. Pneumonitis is the predominant lesion in fatal toxoplasmosis in cats and dogs; placental necrosis with white flecks or multiple white, chalky, necrotic nodules and associated abortion predominate in sheep and goats. Histologcially, this necrosis is confined to the cotyledons where individual and small group of tachyzoites are often difficult to recognize among degenerating host cells. Encephalomyelitis is the predominant lesion in sheep.
Diagnosis
Diagnosis of Toxoplasma is performed at postmortem by identification of organisms in infected tissue. Diagnosis in live animals is aided by serologic tests and by bioassay or xenodiagnosis in mice.
Prevention and Control
The following preventative measures apply to all persons, but because toxoplasmosis is most severe in the perintatal period, they should be emphasized for pregnant women and for young children.
· 1. Avoid contamination with oocysts from cat feces by:
o a. Feeding cats dry, canned or thorougly cooked food
o b. Preventing cats from hunting birds and rodents
o c. Emptying litter boxes daily, before oocysts sporulate
o d. Wearing gloves or thoroughly washing hands after working in the garden or with soil, and before eating or touching the face
o e. Covering children’s sandboxes when not in use
o f. Preventing aerosols in the laboratory during centrifugation of potentially infected biological samples
o g. Boiling drinking water from streams, ponds, or lakes frequented by cats
· 2. Avoid ingestion of tissue cysts by cooking meat to over 660 C and washing hands after handling raw meat.
The following preventative measures apply to farms and other animal-rearing facilities. Avoid contamination of feed or water with oocysts in cat feces by:
· 1. Using rodenticides and traps to prevent cats from hunting rodents
· 2. covering, closing or locking feed-storage facilities to prevent cats from entering and defecating
· 3. Promptly removing cat feces from building stalls or cages; and flushing, burning, or burying them to destroy oocysts
· 4. Providing adequate dry, canned, or thoroughly cooked food and separate water to prevent cats from sharing facilities used by other animals.
Tenia solium T. saginata (Teniasis)
Morphology
T. saginata can be up to 4 to 6 meters long and 12 mm broad; it has a pear-shaped head (scolex) with four suckers but no hooks or neck. It has a long flat body with several hundred segments (proglottids). Each segment is about 18 x 6 mm with a branched uterus (15-30 branches). The egg is 35 x 45 micrometers, roundish and yellow-brown. It has peripheral radial striations and contains an embryo with 3 hooklets.
T. solium is slightly smaller than T. saginata. It has a globular scolex with four suckers and a circular row of hooks (rostellum) that gives it a solar appearance. There is a neck and it has a long flat body (0.1 meter in length). The proglottids are 5 x 10 mm with a 7-12 branch uterus. The eggs of T. solium and T. saginata are indistinguishable.
Life cycle
A tapeworm larval cyst (cysticercus) is ingested with poorly cooked infected meat; the larva escapes the cyst and passes to the small intestine where it attaches to the mucosa by the scolex suckers. The proglottids develop as the worm matures in 3 to 4 months. The adult may live in the small intestine as long as 25 years and pass gravid proglottids with the feces. Eggs extruded from the proglottid contaminate and persist on vegetation for several days and are consumed by cattle or pigs in which they hatch and form cysticerci
Symptoms
Light infections remain asymptomatic, but heavier infections may produce abdominal discomfort, epigastric pain, vomiting and diarrhea.
Cysticercosis
T. solium eggs can also infect humans and cause cysticercosis (larval cysts in lung, liver, eye and brain) resulting in blindness and neurological disorders. The incidence of cerebral cysticercosis can be as high 1 per 1000 population and may account for up to 20% of neurological case in some countries (e.g., Mexico); cysticercosis ocular involvement occurs in about 2.5% of patients and muscular involvement is as high as 10% (India).
Pathology and Immunology
Gastrointestinal symptoms are due to the presence of the tape worm. Cysticercosis symptoms are a result of inflammatory/immune responses. Antibodies are produced in cysticercosis and are useful epidemiological tools.
Diagnosis
Diagnosis is based on the recovery of eggs or proglottids in stool or from the perianal area. Cysticercosis is confirmed by the presence of antibodies.
Treatment and control
Praziquantel is the drug of choice. Expulsion of scolex must be assured to assume a satisfactory treatment. A thorough inspection of beef and pork, adequate cooking or freezing of meat are effective precautions, since cysticerci do not survive temperatures below -
T. saginata can be up to 4 to 6 meters long and 12 mm broad; it has a pear-shaped head (scolex) with four suckers but no hooks or neck. It has a long flat body with several hundred segments (proglottids). Each segment is about 18 x 6 mm with a branched uterus (15-30 branches). The egg is 35 x 45 micrometers, roundish and yellow-brown. It has peripheral radial striations and contains an embryo with 3 hooklets.
T. solium is slightly smaller than T. saginata. It has a globular scolex with four suckers and a circular row of hooks (rostellum) that gives it a solar appearance. There is a neck and it has a long flat body (0.1 meter in length). The proglottids are 5 x 10 mm with a 7-12 branch uterus. The eggs of T. solium and T. saginata are indistinguishable.
Life cycle
A tapeworm larval cyst (cysticercus) is ingested with poorly cooked infected meat; the larva escapes the cyst and passes to the small intestine where it attaches to the mucosa by the scolex suckers. The proglottids develop as the worm matures in 3 to 4 months. The adult may live in the small intestine as long as 25 years and pass gravid proglottids with the feces. Eggs extruded from the proglottid contaminate and persist on vegetation for several days and are consumed by cattle or pigs in which they hatch and form cysticerci
Symptoms
Light infections remain asymptomatic, but heavier infections may produce abdominal discomfort, epigastric pain, vomiting and diarrhea.
Cysticercosis
T. solium eggs can also infect humans and cause cysticercosis (larval cysts in lung, liver, eye and brain) resulting in blindness and neurological disorders. The incidence of cerebral cysticercosis can be as high 1 per 1000 population and may account for up to 20% of neurological case in some countries (e.g., Mexico); cysticercosis ocular involvement occurs in about 2.5% of patients and muscular involvement is as high as 10% (India).
Pathology and Immunology
Gastrointestinal symptoms are due to the presence of the tape worm. Cysticercosis symptoms are a result of inflammatory/immune responses. Antibodies are produced in cysticercosis and are useful epidemiological tools.
Diagnosis
Diagnosis is based on the recovery of eggs or proglottids in stool or from the perianal area. Cysticercosis is confirmed by the presence of antibodies.
Treatment and control
Praziquantel is the drug of choice. Expulsion of scolex must be assured to assume a satisfactory treatment. A thorough inspection of beef and pork, adequate cooking or freezing of meat are effective precautions, since cysticerci do not survive temperatures below -
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