Wednesday, January 23, 2008

 

Protozoa

Parasites
Parasites occur in two distinct forms: single celled protozoa and multi-cellular metazoan called helminthes. [1]

Helminthes
Metazoan are subdivided into two groups: Platyhelminthes and the Nemathelminthes.
The phylum Platyhelminthes contains two important classes: Cestodes and Trematoda. [1]

Cestodes are tapeworms. It consists of two main parts: a rounded head called the scolex which has specialized means of attaching to the intestinal wall and a flat body of multiple segments called proglottids. The oldest proglottids at the distal end produce many eggs which are excreted in the feces and transmitted to various intermediate hosts such as cattle, pigs and fish. Humans usually acquire the infection when undercooked flesh containing the larvae is ingested. [1,2]

Taenia solium: T. solium is found worldwide. Because pigs are intermediate hosts of the parasite, completion of the life cycle occurs in regions where humans live in close contact with pigs and eat undercooked pork. Taeniasis and cysticercosis are very rare in predominantly Muslim countries, as Islam forbids the consumption of pork.[1]

Taenia saginata: T. saginata, also known as Taeniarhynchus saginata or the Beef tapeworm, is a parasite of both cattle and humans, but which can only reproduce in humans. T. saginata occurs where cattle is raised, human feces is improperly disposed of, meat inspection programs are poor, and where meat is eaten without proper cooking.[1]

Echinococcus multilocularis: The definitive hosts are mainly foxes and the intermediate hosts are various rodents. Humans are infected by accidental ingestion of food contaminated with fox feces. [2]

Trematodes are transmitted to humans either via penetration of the skin by the free-swimming cercariae of the schistosomes or via ingestion of cyst in undercooked fish or crabs in Clonorchis and Paragonimus infection, respectively. [1]

Schistosoma japonicum: It causes schistosomiasis. It is found only in Asia and domestic animals such as water buffalos and pigs acts as reservoirs. It is common in tropical and subtropical climates. Most patients are asymptomatic, but chronic infections may become symptomatic. [1]

Nemathelminthes are also known as nematodes. They are commonly classified under: intestinal nematodes and tissue nematodes. Infections with nematodes are associated with conditions of poor hygiene. Such infections are extremely common throughout the tropics and subtropics. [1]

Ancylostoma duodenale and Necator americanus: Humans are infected when filariform larvae in moist soil penetrate the skin. They are found especially in tropical areas. [2]

Strongyloides stercoralis: They are found in the soil. It penetrates the skin and occurs primarily in the tropics, especially SEA.[1]

Wuchereria bancrofti : It occurs in tropical and subtropical areas and is endemic in central Africa, along the Mediterranean coast, and in many parts of Asia, including China, Korea, Japan and the Philippines. [1]


Protozoa

Protozoa are eukaryotic cells and have many of the intracellular components of characteristic of higher forms of life. Most protozoa have some form of active locomotion. Protozoa are found in soil, in most bodies of water, and in many higher forms of life. Relatively few protozoa are able to cause diseases in humans and most are beneficial contributors to the various biological cycles in nature.

Protozoa and other parasitic diseases are common in underdeveloped, tropical, and sub tropical area. The overall effects of these diseases on the general well-being of the inhabitants of these areas are of major importance.

The diagnosis, treatment, and control of protozoal diseases differ in some ways from those used for other microbial diseases. Because of the large size, distinct shapes of the protozoa and that protozoa are difficult to grow on media, direct microscopy is the routine method of diagnosis. The symptoms of many protozoal diseases are very general and often are not used solely as a basis for a specific diagnosis.
Control of protozoal disease is often difficult since human are not the primary host, effective vaccines are not currently available, anti- protozoal drugs are often toxic to the host and close contact between humans and the disease reservoir is fostered by poverty and inadequate education.

Some disease-producing protozoa have a life cycle that involves more than one type of host. The parasite goes through sexual reproduction in the definitive host, whereas asexual reproduction occurs in the intermediate human host. The cell types which are present in a host may be the growing trophozoite (damages tissues) and the dormant, resistant cyst (the form which survives outside a host perpetuating transmission by indirect means.


Reasons for inclusion:

Indonesia is a tropical country with high humidity. In places with high humidity, Food and water can be easily contaminated with fecal products of humans and animals. In the jungle, lakes and water bodies are common. Wild animals’ and human feces may contaminate water and food that the soldiers eat thus infecting them. Swimming in lakes and water bodies may also cause infections as some protozoa can be transmitted through mucosal membranes, trauma and ingestion. Usually in the army, personal hygiene is always overlooked, combined with the poor sanitation of the jungle, it can cause severe infection. During military training, there is also personal time. Soldiers may explore neighboring villages. The soldiers may get infected with diseases during sexual intercourse with women in neighboring villages. In the villages, they may also come into contact with domestic animals.


Entamoeba histolytica [1]

Epidemiology: It is a cosmopolitan intestinal parasite. Organism is acquired by ingestion of cysts that are transmitted primarily by the fecal-oral route in contaminated food and water. Anal- oral transmission, e.g., among male homosexuals, also occurs. There is no animal reservoir. Infection is found worldwide, but occur most frequently in tropical countries, especially in areas with poor sanitation. There are no animal reservoirs.

Causes: Amebic dysentery and liver abscess

Signs and Symptoms:
Asymptomatic infection is common.

Acute intestinal amebiasis: Dysentry (bloody, mucus-containing diarrhea) accompanied by lower abdominal discomfort, flatulence, and tenesmus

Chronic amebiasis: occasional diarrhea, weight loss, and fatigue. Granulomatous lesion called an ameboma may form in the cecal or rectosigmoid areas of the colon.

Amebic abscess (liver): right upper-quadrant pain, weight loss, fever, and a tender, enlarged liver. Right lobe abscesses can penetrate the diaphragm and cause lung disease. Aspiration of the liver abscess yields brownish-yellow pus with the consistency of anchovy-paste.

Mode of Control: Improving basic hygiene and sanitation practices is most effective way of controlling outbreaks of amebiasis as E. histolytica thrives in conditions where standards of sanitation and hygiene are poor. Avoid fecal contamination of food and water and observing good personal hygiene such as hand washing. Water supplies should be purified before drinking. Vegetables should be cooked as it may have been contaminated with human feces.


Giardia lamblia [1.2]

Epidemiology: This organism is a cosmopolitan parasite, common in temperate latitudes and in developed countries, as well as in the tropics. Transmission occurs by ingestion of the cyst in food and water contaminated by feces. The source of infection may be infected human carriers or wild animals that act as reservoirs of infection and contaminate water with the cysts passes in their feces. They pass cyst in the stool which then contaminates the water supplies. Outbreaks are usually related to contaminate water supplies. Drinking of untreated stream water will lead to infection.

Causes: Giardiasis

Signs and Symptoms: Non bloody, foul- smelling diarrhea, nauseam anorexia, flatulence, and abdominal cramps that persist for weeks or months

Mode of Control: Water should be boiled, filtered, or treated with iodine. Frequent hand washing and separation of feeding areas from sanitization area. No vaccine or preventive drug is available.


Plasmodium Species [1]

Epidemiology: The four species are P. vivax, P. falciparum, P. ovale and P. malariae. P. vivax and P. falciparum are the most common causes. The vector and definitive host is the female Anopheles mosquito. Disease is transmitted primarily by the bite of the mosquito. This occurs mainly in the tropical and subtropical areas, especially in Asia.

Causes: Malaria

Signs and Symptoms: Abrupt onset of fever and chills, accompanied by headache myalgias (muscle pain), and aethralgias (joint pains). Fever can reach up 41°C. It is accompanies by shaking chills, nausea, vomiting and abdominal pain. Splenomegaly and hepatomegaly is commonly seen and anaemia is prominent.

P. falciparum can cause extensive brain (cerebral malaria) and kidney (blackwater) damage. (large scale intravascular lysis)

Mode of Control: Chemoprophylaxis of malaria. The use of mosquito netting, window screens, protective clothing and insect repellent can lower the probability of mosquito bites. Elimination of breeding site includes drainage of stagnant water in swamps and ditches, removal of standing water and improvement in land drainage.


Toxoplasma gondii [2]

Epidemiology: Infection by T. gondii occurs worldwide. It is an obligate intracellular parasite widespread among wild and domestic animals. The definitive host is the domestic cat and other felines; humans and other mammals are intermediate host. Cockroaches, flies and earthworms serve as non-infected transport host. Infection begins with the ingestion of cyst in undercooked meats or from contact with cat feces.

Causes: Toxoplasmosis

Signs and Symptoms: Resemble infectious mononucleosis (fever, muscle soreness, sore throat, fatigue)

Mode of control: Control is difficult because of the diversity of animal reservoir. To prevent toxoplasmosis, cook meat thoroughly to kill cyst. Cat should not be fed raw meat as it is the definitive host of the obligate intracellular parasite.


Acanthamoeba castellanii [2]

Epidemiology: They are free-living amoebae. They are found in warm freshwater lakes and in soil. Infection can occur when swimming in the lakes and when there is skin trauma

Causes: Meningeoncephalitis

Signs and Symptoms: eye infection

Mode of Controls: Do not swim in lakes. Avoid traumatized skin contact with lake water or soil.


Naegleria fowleri [1,2]

Epidemiology: N. fowleri thrives in warm water at lower oxygen tensions. It is often found in the mud at the bottom of puddles, ditches, and lakes. It enters the body trough mucous membranes or inhalation while an individual is swimming.

Causes: Meningeoncephalitis

Signs and Symptoms: headache, fever and deteriorates rapidly into coma

Mode of Controls: Do not swim in lakes. Avoid traumatized skin contact with lake water or soil.


Cyclospora cayetanensis [2]

Epidemiology: It is distributed worldwide. Infection appears to be acquired by ingestion of oocytes in water or with contaminated fruits or vegetables.

Causes: “Traveler’s diarrhea”

Signs and Symptons: Water diarrhea with low grade fever and abdominal cramps

Mode of control: Treatment of water supplies with chlorination and filtration. Improving basic hygiene and sanitation practices is most effective way of controlling outbreaks.


Cryptosporidium parvum [1]

Epidemiology: Infection is usually water borne or acquired from animals. Oocytes are present in animal feces and can be transmitted to the human through the fecal- oral route.

Causes: cryptosporidiosis

Signs and Symptoms: Diarrhea leading to fluid loss and malnutrition

Mode of control: Improving basic hygiene and sanitation practices is most effective way of controlling outbreaks. Swimming in lakes or any bodies of water is not advisable.


Trichomonas vaginalis [1,2]

Epidemiology: The primary location is the vagina and the prostate. Transmission of this organism is by sexual contact. It is predominantly a vaginal parasite, although urethritis may occur in the male consorts of infected women. Infection in women is more severe than in men.

Causes: Urinary tract infection

Signs and Symptoms: Pain during urination, discharge

Mode of Control: Abstinence or no unprotected sex


Reasons for exclusion:

Trypanosoma cruzi (Chagas’ disease) [1]
Vector is the reduviid bug. Animal reservoirs include wild species such as the armadillo, raccoon and rat. Rats are commonly found in jungles. However, this disease is common in America only.

Trypanosoma brucei rhodesiense (sleeping sickness) [1]
Wild animals as reservoirs for the tsetse fly, Glossina. Wild animals are abundant in jungles. But this disease occurs primarily in West Africa therefore it is ruled out.

Leishmania donovani [1]
Lifecycle involves the sandfly as the vector and a variety of mammals such as dogs, foxes and rodents as reservoirs. However, this is common in Middle East, Africa, Russia, India and China

Babesia [1,2]
Human infection is rare. Cases reported in Africa, New York, and Southern Europe. In immunocompetent individuals the disease is usually self limiting, so no specific treatment is required.

Isopora belli [2]
It causes self limiting diarrhea in immunocompetenet individuals, but in more severe cases, particularly in patients that are immunocompromised (e.g. AIDS), they will cause severe diarrhea. Medical screening is usually done before enlistment to determine if the individual is healthy. If the individual is immunocompromised, it can be detected during the screening.

Balantidium coli [1,2]
Domestic animals, especially pigs are the main reservoir for the organism. It is commonly associated with pig farming. Humans are infected after ingestion of the cyst in food or water contaminated with animal or human feces. However, it rarely causes disease in humans. Most individual are asymptomatic; diarrhea rarely occurs.


References:
1)Levinson, W. (2006). Review of Medical Microbiology and Immunology. San Francisco,California: Lange Medical Books/ McGraw-Hill Medical Publishing Division

2)Murray, P.R. (2002). Medical Microbiology. St. Louis, Missouri: Mosby Inc.


Done by:
Foo Yong Yang
Loh Mun Jo-anne
TG02

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