Clinical and Basic Parasitology

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Questions and Answers

Which feature typically distinguishes parasites from their hosts?

Parasites provide nutrients to their hosts.

Parasites are larger than hosts.

Parasites have a longer lifespan than hosts.

Parasites outnumber their hosts. (correct)

What type of parasite completely depends on its host for survival?

Temporary parasite

Facultative parasite

Non-pathogenic parasite

Permanent (obligate) parasite (correct)

Which mode of transmission involves a vector organism?

Transplacental

Fecal-oral

Inhalation of contaminated air

Insect bite (correct)

Which of the following is a characteristic of protozoa?

Unicellular and eukaryotic Signup and view all the answers

What is the primary nutritional adaptation of protozoa?

Aerobic heterotrophy Signup and view all the answers

Which type of exposure is least likely to result in parasitic infection?

Consumption of raw vegetables Signup and view all the answers

Which effect can parasites have on their hosts?

Destruction of tissues Signup and view all the answers

Which of the following is a type of helminth?

Roundworms Signup and view all the answers

Which reproductive method is used by protozoa?

Asexual binary fission Signup and view all the answers

How do ciliates primarily intake food?

Moving cilia toward a mouth-like opening Signup and view all the answers

What is the primary mode of transmission for Entamoeba histolytica?

Fecal-oral transmission of cyst Signup and view all the answers

Which organism is primarily responsible for causing malaria?

Anopheles mosquito Signup and view all the answers

Which of the following characteristics is true for Trichomonas vaginalis?

It leads to asymptomatic infections in most men. Signup and view all the answers

What disease is associated with Toxoplasma gondii infections?

Toxoplasmosis Signup and view all the answers

How does Giardia lamblia primarily affect the host?

By interfering with food absorption in the intestines Signup and view all the answers

What is the typical clinical manifestation of cryptosporidiosis caused by Cryptosporidium parvum?

Watery, non-bloody diarrhea Signup and view all the answers

Which of the following treatments is commonly used for giardiasis?

Metronidazole plus Quinacrine hydrochloride Signup and view all the answers

What is a key preventive measure for avoiding transmission of Toxoplasma gondii?

Cooking meat thoroughly Signup and view all the answers

Which of the following is NOT a characteristic of helminths?

Non-reproductive Signup and view all the answers

What is the primary vector responsible for transmitting Chagas disease?

Reduviid bug Signup and view all the answers

What is the primary mode of transmission for Ascariasis?

Food contaminated by soil containing eggs Signup and view all the answers

What symptoms can result from the migration of larvae in Ascariasis?

Pulmonary symptoms Signup and view all the answers

What type of hookworms is primarily associated with blood loss?

Ancylostoma duodenale and Necator americanus Signup and view all the answers

Which of the following is a preventive measure for Trichinosis?

Adequate cooking of pork Signup and view all the answers

What is a significant complication associated with Wuchereria bancrofti infection?

Obstruction of lymphatic vessels Signup and view all the answers

What treatment is effective against the microfilariae of Onchocerca volvulus?

Ivermectin Signup and view all the answers

What is the initial symptom of Dracunculiasis?

Ulceration of the skin Signup and view all the answers

What is the primary vector for Onchocerca volvulus?

Black flies Signup and view all the answers

In which condition might patients experience massive super-infection due to the larval presence?

Strogyloidiasis Signup and view all the answers

What is a common clinical effect of Loa loa infection?

Calabar swelling Signup and view all the answers

What is the primary treatment for hydatid cyst disease caused by Echinococcus granulosus?

Surgical removal of cyst Signup and view all the answers

What symptom is most prominently associated with Enterobius vermicularis infection?

Perianal pruritus Signup and view all the answers

Which organism is associated with megaloblastic anemia due to vitamin B12 deficiency?

Diphyllobothrium latum Signup and view all the answers

What is the definitive action recommended for preventing Taenia solium infection?

Adequate cooking of pork Signup and view all the answers

What is the most common symptom observed with Trichuris trichiura infection?

Asymptomatic Signup and view all the answers

How does the adult Diphyllobothrium latum typically affect a patient's health?

Most patients remain asymptomatic Signup and view all the answers

What is the correct method for treating Schistosoma spp. infection?

Praziquantel Signup and view all the answers

What is a consequence of cysticercosis in the brain?

Headache and seizures Signup and view all the answers

What type of food is associated with the transmission of Chlonorchis sinensis?

Raw or undercooked freshwater fish Signup and view all the answers

What is the primary mode of transmission for Taenia saginata?

Eating raw or undercooked beef Signup and view all the answers

Study Notes

Parasitology

A parasite is an organism that lives in or on another organism (host) and depends on it for survival.
Parasites are typically smaller than their hosts and have a shorter lifespan.
They have a greater reproductive potential than their hosts to ensure their survival.

Classification of Parasites

Habitat:
- Endoparasites: Live inside the host (e.g., intestinal worms).
- Ectoparasites: Live on the surface of the host (e.g., ticks).
Effect on host:
- Pathogenic: Cause disease in the host.
- Non-pathogenic: Do not cause disease in the host.
Mode of living:
- Permanent (obligate): Completely dependent on the host for survival.
- Temporary (facultative): Capable of independent existence, but can also be parasitic.

Sources of Parasitic Infections

Contaminated soil
Contaminated water
Insufficiently cooked meat (pork, beef)
Blood-sucking arthropods (e.g., mosquitoes, flies)
Animals
Human beings
Sexual intercourse

Mode of Transmission

Fecal-oral
Sexual intercourse
Blood transfusion
Direct skin penetration
Transplacental
Transmammary
Insect bite
Inhalation of contaminated air

Effects of Parasites on Hosts

Consumption of host's nutrients
Obstruction of passages
Bleeding
Destruction of tissues
Compression of vital organs
Release of toxic substances
Allergic reactions
Predisposition to cancer

Protozoa

Unicellular, eukaryotic organisms.
Found in soil and water.
Reproduction:
- Asexually: Binary fission, budding, or schizogony.
- Sexually: Conjugation.
Encystment: Protozoa can form protective cysts for survival in harsh conditions.
Nutritional Adaptation: Most are aerobic heterotrophs, but some can grow anaerobically.
Feeding:
- Ciliates: Utilize cilia to move food towards the cytostome (mouth-like opening).
- Amoebas: Engulf food by phagocytosis.
Digestion occurs within vacuoles.

Helminths (Worms)

Multicellular, eukaryotic animals consisting of digestive, circulatory, nervous, excretory, and reproductive systems.
Life cycle:
- Dioecious: Separate male and female individuals.
- Monoecious/hermaphroditic: Single individual possesses both male and female reproductive organs.

Clinical Parasitology

Intestinal Protozoa

Entamoeba histolytica:
- Causes amoebic dysentery (amoebiasis) and liver abscess.
- Transmission: Fecal-oral, oral-anal transmission in homosexuals.
- Pathogenesis: Multiplies in the large intestine, causing dysentery with blood and mucus in feces. Can lead to intestinal perforation and liver abscess.
- Treatment: Metronidazole and iodoquinol.
- Prevention: Avoid fecal contamination of food and water. Proper disposal of human waste. Cook food thoroughly and boil water.
Giardia lamblia:
- Causes giardiasis.
- Transmission: Fecal-oral transmission of cysts.
- Pathogenesis: Cysts attach to the duodenum, causing inflammation and interfering with nutrient absorption. Results in non-bloody, foul-smelling diarrhea, nausea, anorexia, flatulence, and abdominal cramps.
- Treatment: Metronidazole and quinacrine hydrochloride.
- Prevention: Boil and filter water (chlorination ineffective).
Cryptosporidium parvum:
- Causes cryptosporidiosis (cholera-like diarrhea).
- Transmission: Fecal-oral transmission of cysts.
- Pathogenesis: Cysts attach to the jejunum, producing watery, non-bloody diarrhea and fluid loss.
- Treatment: No effective drug therapy. Oral rehydration recommended.
- Prevention: Chlorination and filtration ineffective. No reliable prevention methods currently exist.

Urogenital Protozoa

Trichomonas vaginalis:
- Causes trichomoniasis.
- Transmission: Sexual contact.
- Pathogenesis: Attaches to the vagina in women and urethra in men, causing inflammation. In women, it causes a watery, foul-smelling greenish discharge, itching, and burning. Men are often asymptomatic but 10% experience urethritis.
- Treatment: Metronidazole for both partners.
- Prevention: Condoms help limit transmission.

Blood and Tissue Protozoa

Plasmodium sp. (P. vivax, P. ovale, P. malariae, P. falciparum):
- Causes malaria.
- Transmission: Bite of female Anopheles mosquito.
- Pathogenesis: Mosquito injects sporozoites into bloodstream. Sporozoites enter liver cells, multiply through schizogony, and release merozoites into the blood to infect red blood cells.
- Clinical features: Abrupt onset of fever, chills, headache, and myalgias after a 2-week incubation period. Fever accompanied by nausea, vomiting, abdominal cramps, and drenching sweats.
- Treatment: Chloroquine, mefloquine, sulfadoxine, pyrethamine, primaquine.
- Prevention: Chemoprophylaxis and mosquito control.
Toxoplasma gondii:
- Causes toxoplasmosis.
- Transmission: Ingestion of cysts in undercooked meat, contact with cat feces, and transplacental transmission.
- Pathogenesis: Trophozoites infect various organs (brain, eyes, liver), forming cysts that persist in tissues.
- Clinical features: Most initial infections are asymptomatic. Congenital infections can lead to abortion, stillbirth, encephalitis, mental retardation, and visual problems.
- Treatment: Sulfonamides and pyrethamine for congenital and disseminated disease.
- Prevention: Cook meat thoroughly. Pregnant women should avoid handling cats.
Trypanosoma cruzi:
- Causes Chagas' disease (American trypanosomiasis).
- Transmission: Bite of reduviid bug.
- Pathogenesis: Organism attacks cardiac muscles, causing inflammation and cardiac arrhythmias. Destroys nerves controlling esophageal and colonic peristalsis, leading to megacolon and megaesophagus.
- Clinical features: Acute phase marked by facial edema and a nodule (chagoma) near the bite site, accompanied by fever, lymphadenopathy, and hepatosplenomegaly. Most remain asymptomatic but some progress to the chronic form characterized by megacolon and megaesophagus. Death is due to cardiac failure.
- Treatment: Nifurtimox.
- Prevention: Protection from bug bites and insect control.
Trypanosoma gambiense & Trypanosoma rhodesiense:
- Cause sleeping sickness (African trypanosomiasis).
- Transmission: Bite of tsetse fly.
- Pathogenesis: Spreads from skin to lymph nodes and eventually to the brain causing encephalitis.
- Clinical features: Acute form with cyclical fever spikes every 2 weeks. Initial lesion is an undulating skin ulcer (trypanosomal chancre). Encephalitis occurs with insomnia, mood changes, muscle tremors, slurred speech, and progressive somnolence leading to coma. Untreated disease is usually fatal due to pneumonia.
- Treatment: Suramin in early disease, suramin plus melarsoprol if CNS symptoms occur.
- Prevention: Protection from bug bites.
Leishmania donovani:
- Causes kala-azar (visceral leishmaniasis) or dum dum fever.
- Transmission: Bite of sandfly (Phlebotomus or Lutzomyia).
- Pathogenesis: Amastigotes kill reticulo-endothelial cells, particularly in the liver, spleen, and bone marrow.
- Clinical features: Symptoms begin with intermittent fever, weakness, and weight loss. Massive enlargement of the spleen. Gastro-intestinal bleeding.
- Treatment: Sodium stibogluconate.
- Prevention: Protection from sandfly bites.
Leishmania tropica & L. mexicana:
- Cause cutaneous leishmaniasis.
Leishmania brasiliensis:
- Cause mucocutaneous leishmaniasis.

Cestodes (Tapeworms)

Taenia solium (pork tapeworm):
- Causes taeniasis and cysticercosis.
- Transmission: Eating raw or undercooked pork containing larvae.
- Pathogenesis: Larvae attach to the intestinal wall and grow into adult worms (up to 5 meters long) with little damage to the intestine. Eggs can enter the bloodstream and spread to various organs, particularly the brain.
- Clinical features: Most adults with tapeworms are asymptomatic, but anorexia and diarrhea can occur. Cysticercosis in the brain causes headache, vomiting, and seizures. Cysticercosis in the eyes can lead to retinitis or visible larvae in the vitreous humor.
- Treatment: Niclosamide for intestinal worms, praziquantel for cerebral cysticercosis.
- Prevention: Cook pork thoroughly.
Taenia saginata (beef tapeworm):
- Causes taeniasis.
- Transmission: Eating raw or undercooked beef containing larvae.
- Pathogenesis: Larvae attach to the intestinal wall and grow into adult worms (up to 6 meters long) with little damage to the intestine.
- Clinical features: Most patients are asymptomatic except for vague abdominal discomfort.
- Treatment: Niclosamide.
- Prevention: Cook beef thoroughly. Proper disposal of human waste.
Diphyllobothrium latum (fish tapeworm):
- Causes diphyllobothriasis.
- Transmission: Eating raw or undercooked freshwater fish containing larvae.
- Pathogenesis: Larvae attach to the intestinal wall, growing into adult worms (up to 13 meters long) with little damage to the intestine. Can also cause megaloblastic anemia due to vitamin B12 deficiency.
- Clinical features: Most patients are asymptomatic but abdominal discomfort and diarrhea can occur.
- Treatment: Niclosamide.
- Prevention: Cook fish thoroughly. Proper disposal of human waste.
Echinococcus granulosus (dog tapeworm):
- Causes hydatid cyst disease.
- Transmission: Ingestion of eggs in food contaminated with dog feces.
- Pathogenesis: Eggs migrate to various organs (liver, lungs, brain), developing into hydatid cysts. Cyst rupture can cause anaphylaxis.
- Clinical features: Many patients with hydatid cysts are asymptomatic. Liver cysts can cause hepatic dysfunction. Lung cysts can erupt into the bronchus causing bloody sputum. Brain cysts cause headache and focal neurological signs.
- Treatment: Surgical removal of cysts. Mebendazole can be used in inoperable cases.

Trematodes (Flukes)

Schistosoma spp. (S. mansoni, S. japonicum, S. hematobium) (blood flukes):
- Causes schistosomiasis.
- Transmission: Penetration of the skin by free-swimming eggs/larvae.
- Pathogenesis: After skin penetration, they enter the bloodstream and travel to the liver where they mature into adult flukes. S. mansoni damages the distal colon while S. japonicum damages both small and large intestines. S. hematobium forms granulomas and fibrosis in the bladder wall which can lead to carcinoma of the bladder.
- Clinical features: After skin penetration, itching and dermatitis occur. 2-3 weeks later, fever, chills, diarrhea, and hepatosplenomegaly develop. Chronic stages include GIT bleeding.
- Treatment: Praziquantel.
- Prevention: Proper disposal of human waste. Avoid swimming in endemic areas..
Clonorchis sinensis (liver fluke):
- Causes clonorchiasis.
- Transmission: Eating raw or undercooked freshwater fish containing larvae.
- Pathogenesis: After ingestion, they invade the duodenum and enter the biliary ducts where they mature into adults. Inflammatory response can cause hyperplasia and fibrosis of the biliary tract, but often there are no lesions.
- Clinical features: Most infections are asymptomatic. Heavy worm burdens can cause upper abdominal pain, anorexia, and hepatomegaly.
- Treatment: Praziquantel.
- Prevention: Cook fish thoroughly. Proper waste disposal.
Paragonimus westermani (lung fluke):
- Causes paragonimiasis.
- Transmission: Eating raw or undercooked crab meat containing larvae.
- Pathogenesis: Immature flukes penetrate the intestinal wall through the diaphragm into the lungs, differentiating into adult eggs that enter the bronchioles and are coughed up and swallowed.
- Clinical features: Main symptom is chronic cough with bloody sputum, resembling tuberculosis. Dyspnea, chest pain, and recurrent attacks of bacterial pneumonia can also occur.
- Treatment: Praziquantel.
- Prevention: Cook crabs thoroughly.

Nematodes (Roundworms)

Intestinal Nematodes

Enterobius vermicularis (pinworm):
- Causes pinworm infection.
- Transmission: Ingestion of eggs.
- Pathogenesis: Adult male and female worms live in the colon, where mating occurs. At night, the female migrates to the anus and releases thousands of fertilized eggs into the environment. These eggs develop into larvae within 6 hours and become infectious. Reinfection can occur when the eggs are carried to the mouth by fingers after scratching the itching skin. Ingested eggs hatch in the small intestine, and larvae differentiate into adults and migrate to the colon.
- Clinical features: Perianal pruritus is the most prominent symptom. Scratching predisposes to secondary bacterial infection.
- Treatment: Mebendazole or pyrantel pamoate.
- Prevention: No reliable prevention methods currently exist.
Trichuris trichiura (whipworm):
- Causes whipworm infection.
- Transmission: Ingestion of eggs in food or water contaminated with soil containing eggs.
- Pathogenesis: Eggs hatch in the small intestine, where larvae differentiate into immature worms. They migrate to the colon, where they mature, mate, and produce thousands of fertilized eggs daily, which are passed in feces. Eggs deposited in warm, moist soil form embryos.
- Clinical features: Most infections are asymptomatic.
- Treatment: Mebendazole.
- Prevention: Proper disposal of human waste.
Ascaris lumbricoides (roundworm):
- Causes ascariasis.
- Transmission: Ingestion of eggs in food contaminated by soil containing eggs.
- Pathogenesis: Eggs hatch in the small intestine, and larvae migrate to the bloodstream and lungs. They enter the alveoli, pass up the bronchi and trachea, and are swallowed. Within the small intestine, they mature into adult worms (up to 30 cm long). Thousands of eggs are laid daily, passed in feces, and form embryos in warm, moist soil.
- Clinical features: Larvae in the lungs can cause pulmonary symptoms (ascaris pneumonia). Malnutrition and worm migration (mouth, ears, nose) are other common features.
- Treatment: Mebendazole or pyrantel pamoate.
- Prevention: Proper disposal of human waste.
Ancylostoma duodenale & Necator americanus (hookworms):
- Cause hookworm infection.
- Transmission: Larvae in soil penetrate the skin of feet and legs.
- Pathogenesis: After skin penetration, they are carried by the blood to the lungs, migrate to the alveoli, move up the trachea, and are swallowed. They mature into adults in the small intestine and attach to its wall. They feed on blood and tissue of the intestinal villi. Thousands of eggs are laid per day and passed in feces.
- Clinical features: Loss of blood at the site of attachment (0.1-0.3 ml per worm), leading to weakness and pallor.
- Treatment: Mebendazole or pyrantel pamoate.
- Prevention: Use of footwear. Proper disposal of human waste.
Strongyloides stercoralis:
- Causes strongyloidiasis.
- Transmission: Larvae in soil penetrate the skin of feet and legs.
- Pathogenesis: After penetration, larvae enter the blood and migrate to the lungs, moving into the alveoli, up the trachea, and are swallowed. They become adults in the colon and are passed in feces.
- Clinical features: Little effect in healthy individuals. In immunocompromised persons, massive superinfection can occur, accompanied by secondary bacterial infection.
- Treatment: Thiabendazole.
- Prevention: Proper disposal of human waste. Use of footwear.
Trichinella spiralis:
- Causes trichinosis.
- Transmission: Eating raw or undercooked meat (pork).
- Pathogenesis: Larvae mature into adults within the mucosa of the small intestine. Eggs hatch within adult females, and larvae are released via the bloodstream to various organs.
- Clinical features: Gastroenteritis occurs a few days after eating infected pork. One to two weeks later, fever, muscle pain, and periorbital edema develop. Signs of cardiac and CNS disease are frequent due to larval migration. Death (rare) occurs due to CHF and respiratory paralysis.
- Treatment: Thiabendazole or mebendazole to kill adult worms. Corticosteroids to reduce inflammation.
- Prevention: Cook pork adequately.

Tissue Nematodes

Wuchereria bancrofti:
- Causes filariasis (elephantiasis).
- Transmission: Bite of female Anopheles and Culex mosquitoes.
- Pathogenesis: Larvae penetrate the skin, enter the lymph nodes, and mature into adults after a year, producing microfilariae. Microfilariae circulate in the blood, primarily at night, and are ingested by biting mosquitoes. Within the mosquito, they produce infective larvae that are transferred with the next bite.
- Clinical features: Adult worms in the lymph nodes cause inflammation that eventually obstructs lymphatic vessels. Fever, lymphangitis, and cellulitis develop. Obstruction leads to edema of the legs and genitals.
- Treatment: Diethylcarbamazine for microfilariae. No drug therapy for adult worms.
- Prevention: Mosquito control.
Onchocerca volvulus:
- Causes onchocerciasis (river blindness).
- Transmission: Bite of female black flies.
- Pathogenesis: Blackflies deposit infective larvae while biting. Larvae enter the wound and migrate into subcutaneous tissue, where they mature into adults. Females produce microfilariae that are ingested by another blackfly. Within the mosquito, they develop into infective larvae.
- Clinical features: Inflammation occurs in subcutaneous tissue, forming pruritic papules and nodules. Microfilariae migrate in the eyes, leading to blindness.
- Treatment: Ivermectin is effective for microfilariae but not adult worms. Suramin is used for eye infections. Skin nodules can be surgically removed.
- Prevention: Black fly control.
Loa loa:
- Causes loiasis.
- Transmission: Bite of deer fly.
- Pathogenesis: Deer flies deposit infective larvae on the skin. Larvae enter the bite wound, wander in the body, and develop into adult worms. Females release microfilariae, which enter the blood, particularly during the day. These microfilariae are taken up by another deer fly during a blood meal and differentiate into infective larvae.
- Clinical features: No inflammatory response to microfilariae, but hypersensitivity reactions cause transient, localized, non-erythematous, subcutaneous edema (Calabar swelling). Adult worms crawling across the conjunctiva of the eyes.
- Treatment: Diethylcarbamazine. Worms in the eyes may require surgical excision.
- Prevention: Deer fly control.
Dracunculus medinensis:
- Causes dracunculiasis.
- Transmission: Ingestion of crustaceans containing infective larvae in drinking water.
- Pathogenesis: After ingestion, larvae are released in the small intestine and migrate in the body, where they become adults. Meter-long females cause the skin to ulcerate and then release motile larvae into fresh water. Crustaceans eat these larvae and form infective larvae.
- Clinical features: Inflammation, blistering, and ulceration of the skin, especially the lower extremities. The inflamed papule burns and itches, and the ulcer can become secondarily infected.
- Treatment: Niridazole and worm extraction.
- Prevention: Purification of drinking water.

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