Medically Important Protozoa (3)

Cryptosporidiosis. Cryptosporidium parvum causes diarrhea disease mainly in infants and small children. It is normally self-limiting but in the immunocompromized host the disease can be severe. C. parvum is enzootic in young calves and is usually passed to man in water containing oocysts of the organism. Toxoplasmosis. Toxoplasma gondii causes the multi-organ infection of toxoplasmosis. The domestic cat is the definitive host for T. gondii from which man and other mammals can become infected. Infection commonly arises from the consumption of under cooked meat and in the healthy adult is usually asymptomatic. The most devastating form of toxoplasmosis is seen in congenital infection when a pregnant mother passes the organism to the fetus. This can result in severe abnormalities at birth. The life-cycle of T. gondii is complex, involving both sexual and asexual reproduction. Three main life forms of T. gondii occur: (i) the oocyst which is produced from the sexual cycle in the small intestine of the cat and contains sporozoites; (ii) the tachyzoite of the asexual invasive form found in secondary hosts which are derived from pseudocysts; and (iii) the tissue cyst that contains bradyzoites.
Microsporans
The medical importance of microsporidial infections has only recently been highlighted by the frequent recognition of these obligate intracellular parasites in material from patients with HIV infection and AIDS. Examples are: Encephalitozoon species, Nosema species and Septata intestinalis. Multi-organ infections occur and S. intestinalis is found in about 2% of all AIDS patients with chronic diarrhea.
Source: University of Leicester
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.

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Medically Important Protozoa (2)

Leishmania species cause leishmaniasis. The disease is spread by the bite of sandflies in which part of the organism's life cycle is completed. In man, the promastigotes from the bite of the sandfly become ingested by macrophages and multiply within them as amastigotes. Cutaneous
leishmaniasis occurs if the region of infection remains localized to the dermis as an open sore. In the Old World (Southern Europe, the Middle East, India, former USSR and parts of Africa) L. major, L. tropica, L. aethiopica and certain subtypes of L. infantum are responsible. In the New World (Mexico southwards and through South America) species responsible include L. braziliensis, L. mexicana and L. amazonensis. If the organism spreads, then mutocutaneous leishmaniasis can occur in which the nose, mouth and palate becomes destroyed. Infection with members of the L. donovani-L.infantum complex produce the systematic disease of visceral leishmaniasis often known as kala-azar that occurs with a global distribution seen in Old and New World leishmaniasis. The parasites multiply within the macrophages of the liver, spleen, bone marrow and other organs. Untreated, the disease is usually fatal. As with trypanosomiasis, leishmaniasis is a zoonosis as many mammals harbor the parasite.
Ciliates
These possess rows of cilia around the outside of the body that aid motility. The only member of this group known to infect man is Balantidium coli. This is a cyst forming parasite that is a commensal ("table-sharing" and meaning here a non-pathogenic parasite) of domestic and wild pigs. It does, however, cause severe diarrhea in humans.
Apicomplexa
This is a unique group because all members are parasitic. The group includes parasites causing malaria, cryptosporidiosis and toxoplasmosis. They lack any visible means of locomotion (most are intracellular) and have complex life cycles involving sexual and asexual reproduction.. The common feature of all members is the presence of an apical complex in one or more stages of the life cycle. Although the exact components of the apical complex varies among members, it contains enzymes used to penetrate host tissues.
Malaria. Plasmodium species cause malaria. The four principal species are P. falciparum, P. vivax, P. ovale and P. malariae. Malaria means "bad air" and dates from the time when the disease was thought to be spread from stagnant, foul smelling water. The disease is in fact transmitted by the female Anopheles mosquito that inhabits such environments. In the stomach of the female Anopheles male (micro-) and female (macro-) gametocytes fuse to form a zygote. This in turn forms a motile ookinete that penetrates the midgut wall and develops into an oocyst within which are many thousands of sporozoites. When mature, the sporozoites rupture the oocyst and penetrate the salivary glands. When the mosquito next feeds on man, the sporozoites are passed via the blood stream to infect parenchymal cells of the liver. Here they form pre-erythrocytic schizonts in which several thousand daughter cells, called merozoites. These merozoites enter red blood cells to start the asexual intraerythrocytic cycle and form new gametocytes. The asexual red cell stages are responsible for the pathological changes that occur in malaria (fever, chills, anemia, liver enlargement, encephalitis renal damage and death).

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Strongyloides westeri

Merupakan cacing nematoda. Terdapat diseluruh dunia pada mukosa usus halus kuda, keledai, dan zebra. Cacing ini biasanya tidak banyak. Mereka mempunyai oesophagus sangat panjang dan berbentuk hamper silindris, vulva pada bagian pertengahan tubuh posterior, ekor pendek berbentuk kerucut, uterus amfidelf (dengan cabang ke depan maupun ke belakang). Cacing betina panjangnya 8-9 mm dan berdiameter 80-95 mikron; mereka menghasilkan telur berembrio berbentuk elips, berkulit tipis, berukuran 40-52 x 32-40 mikron, masa prepaten sekitar 2 minggu. Hanya cacing betina yang bersifat partenogenetik.
Infeksi Strongyloides westeri dapat didiagnosa dengan cara menemukan telur-telurnya pada tinja atau nematode itu sendiri dengan pemeriksaan mikroskopik pada kerokan karena selaput lendir terutama dari duodenum pada saat pemeriksaan bedah bangkai. Akan tetapi, larva yang bermigrasi dapat menyebabkan radang paru-paru pada anak kuda, sebelum mereka menjadi dewasa dan mulai bertelur. Perlu ditekankan bahwa bagaimanapun telur yang banyak pada feses mungkin ditemukan juga pada hewan yang sehat.

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OOSISTA PADA KUDA

Eimeria leukarti
Eimeria leukarti biasanya berlokasi diusus halus kuda dan dapat menyebabkan diare intermiten. Eimeria leukarti mempunyai periode prepaten ± 15 hari. Oosista berisi 4 sporosista dengan tiap sporokista berisi 2 sporozoit. Ookista berbentuk oval atau piriform, sangat besar sekitar 80 x 60 µm dengan dinding kasar berlapis dua (gelap dan tebal) dan mempunyai mikropile berbeda. Patologi keradangan ditandai dengan adanya perubahan mukosa dan gangguan pada struktur vili. Hasil diagnosa sangat sulit, dan karena dinding oosista yang tebal maka harus dilakukan teknik sedimentasi, atau jika menggunakan taknik pengapungan maka diperlukan larutan gula jenuh.

Klossella
Klossiella equi terdapat pada ginjal kuda. Ookista yang telah tumbuh penuh berupa kantung berdinding tipis 50-90 x 35 µm mengandung sebanyak 40 sporokista seperti bentuk telur ± 8-10 x 4-5 µm, masing-masing dengan 8-12 sporozoit.

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Leucocytozoonosis

Leucocytozoonosis adalah penyakit yang disebabkan oleh parasit darah Leucocytozoon sp. yang dapat menyebabkan kematian dan terhambatnya pertumbuhan pada anak ayam. Penyakit ini untuk pertama kali dilaporkan oleh Dr. Theobold Smith (1895) pada seke­lompok kalkun yang terserang di Amerika Serikat bagian Timur. Pada ayam dewasa menimbulkan penurunan produksi telur dan pada kal­kun dapat menimbulkan penurunan daya tetas telur. Penyakit ini me­nyerang beberapa jenis unggas antara lain: itik dan angsa oleh Leuco­cytozoon neavei, Leucocytozoon numidae, Leucocytozoon costai dan Leucocytozoon simondi; kalkun oleh Leucocytozoon smithi; ayam oleh Leucocytozoon cauleryi, Leucocytozoon andrewsi; Leuco­cytozoon schoutedeni dan Leucocytozoon Sabrasezi.
Penularan terjadi melalui gigitan Sinulium sp (lalat hitam), Culi-coides sp dan Ornithophilous sp yang bertindak selaku perantara. Penyakit yang akut biasa terjadi pada waktu menjelang dan sewaktu musim panas pada saat populasi lalat hitam meningkat.
Gejala klinis dipengaruhi oleh umur dan jenis hewan yang terse­rang. Gejala klinis yang terlihat umumnya adalah terjadinya penurun­an nafsu makan, haus, depresi, bulu kusut dan pucat. Ayam kehi­langan keseimbangan, lemah, pernafasan cepat dan anemi. Kejadian penyakit berlangsung secara cepat. Ayam dapat mati atau sembuh dengan sendirinya. Angka kematian dapat mencapai 10% - 80%.
Perubahan paling menonjol adalah pembesaran limpa dan biasa­nya hati juga membengkak. Otot daging lembek, pucat dan terjadi perdarahan titik yang merata. Perdarahan kecil juga ditemukan pada lapisan luar usus.
Diagnosis secara klinis dilakukan berdasar gejala dan sejarah kejadian dalam kelompok. Diagnosis ini dapat diperteguh dengan pengujian sediaan ulas darah yang mengandung schizont protozoa sebagai agennya. Untuk keperluan ini sediaan ulas dikirim ke labo­ratorium dengan fiksasi kering udara. Potongan organ terutama paru, hati, limpa dan jantung dikirim dalam formalin 10% ke BPPH atau laboratorium yang terdekat.

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Medically Important Protozoa (1)

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.

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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.

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