parasites

What is the definition of symbiosis?

An association between two different species exhibiting metabolic dependence.

What is the definition of parasitism?

An association where one species (parasite) lives in or on another (host) and is metabolically dependent on it.

What is a definitive host?

The animal in which a parasite passes its adult, sexual reproductive phase.

What is an intermediate host?

The animal in which a parasite passes its larval or asexual reproduction phase.

What is a reservoir host?

An animal that harbors a parasite that is also parasitic for humans.

What is the infective stage?

The parasite stage that is infective to a new host.

What is the diagnostic stage?

The parasite stage that leaves the human host and can be detected in a lab.

Why is it critical to collect specimens before starting antimicrobial therapy?

Therapy can reduce or eliminate parasites, leading to a false-negative result.

Why should a fecal specimen NOT be contaminated with water?

Water may contain free-living organisms that can be mistaken for human parasites.

Why should a fecal specimen NOT be contaminated with urine?

Urine can destroy motile trophozoites.

What is the preferred anticoagulant for blood specimens for parasitology?

EDTA.

Why is EDTA the preferred anticoagulant for blood parasite morphology?

It provides better preservation of organism morphology, especially for Plasmodium.

What is the critical handling requirement for a CSF specimen suspected of containing Naegleria fowleri?

It must never be refrigerated.

What is the purpose of the direct wet mount?

To detect motile protozoan trophozoites in fresh stool.

What is the primary goal of a fecal concentration technique?

To increase the chance of finding parasites by separating them from fecal debris.

Which fecal concentration method is best for recovering all parasite stages, including heavy, operculated eggs?

Sedimentation (e.g., Formalin-Ethyl Acetate).

Which fecal concentration method provides a cleaner preparation but may miss operculated eggs?

Flotation (e.g., Zinc Sulfate).

What is considered the most important procedure for the definitive identification of intestinal protozoa?

The permanent stained smear.

What is the purpose of the thick blood smear?

To screen a large volume of blood for the presence of parasites (high sensitivity).

What is the purpose of the thin blood smear?

To identify the species of blood parasites and calculate parasitemia (high specificity/detail).

What is the justification for performing both a thick and thin blood smear?

Their roles are complementary: the thick smear for detection and the thin smear for identification.

What is the primary advantage of using molecular assays (like PCR) in parasitology?

High sensitivity and specificity; can differentiate morphologically identical species.

What single morphological feature definitively identifies a trophozoite as the pathogen Entamoeba histolytica?

The presence of ingested red blood cells (RBCs).

Why is it important to report the presence of nonpathogenic intestinal parasites?

Their presence indicates a route of fecal-oral contamination has occurred.

What is the general term for the motile, feeding, and reproducing stage of a protozoan?

Trophozoite.

What is the general term for the non-motile, infective, and environmentally resistant stage of a protozoan?

Cyst.

What disease is caused by Entamoeba histolytica?

Amebiasis (including amebic dysentery and liver abscesses).

How is Giardia lamblia infection acquired?

Ingestion of cysts from contaminated water or food.

What is the characteristic motility of Giardia lamblia trophozoites described as?

"Falling-leaf" motility.

What is the infective stage of Plasmodium species for humans?

Sporozoites (injected by a mosquito).

What is the diagnostic stage of Plasmodium species in human blood?

Asexual blood stages (rings, trophozoites, schizonts) and gametocytes.

What is the characteristic shape of Plasmodium falciparum gametocytes? (image)

Crescent-shaped.

What is the vector for Leishmaniasis?

The sand fly.

What is the vector for African Trypanosomiasis (Sleeping Sickness)?

The tsetse fly.

What is the vector for American Trypanosomiasis (Chagas' Disease)?

The reduviid bug (kissing bug).

What is the intracellular stage of Leishmania and Trypanosoma cruzi found in human tissues?

Amastigote.

What is the motile stage of Trypanosoma found in human blood?

Trypomastigote.

What is the infective stage of Ascaris lumbricoides?

Embryonated egg.

What is the diagnostic stage of Ascaris lumbricoides?

Fertilized or unfertilized eggs in feces.

What is the mode of infection for hookworms (Necator americanus, Ancylostoma duodenale)?

Skin penetration by filariform larvae from contaminated soil.

What is the key feature of the Strongyloides stercoralis life cycle that can lead to persistent, long-term infections?

Autoinfection.

What is the diagnostic stage of Enterobius vermicularis (pinworm)?

Eggs collected from the perianal skin.

What is the most common symptom of enterobiasis?

Perianal itching (pruritus ani).

What is the primary pathology associated with heavy hookworm infections?

Iron deficiency anemia due to chronic blood loss.

How are microfilariae differentiated in a blood smear?

Presence or absence of a sheath and the pattern of nuclei in the tail.

Which microfilaria is sheathed, with nuclei that do not extend to the tip of the tail? (image)

Wuchereria bancrofti.

Which microfilaria is sheathed, with nuclei that are continuous to the tip of the tail? (image)

Loa loa.

What is a zoonotic infection?

A disease of animals that can be transmitted to humans.

What disease is caused by the larval stage of Taenia solium in humans?

Cysticercosis (neurocysticercosis if in the brain).

How do humans acquire intestinal taeniasis from Taenia saginata?

Ingestion of cysticerci in undercooked beef.

How do humans acquire cysticercosis from Taenia solium?

Ingestion of eggs from human feces (fecal-oral route).

What is the characteristic feature of the scolex of Taenia solium? (image)

Four suckers and a rostellum with hooks.

What is the characteristic feature of the scolex of Taenia saginata? (image)

Four suckers but no rostellum or hooks.

What is the diagnostic stage of Diphyllobothrium latum (fish tapeworm)?

Operculated eggs in feces.

What vitamin deficiency can be caused by Diphyllobothrium latum infection?

Vitamin B12 deficiency.

What is the infective stage of schistosomiasis for humans?

Cercariae penetrating the skin from contaminated water.

Which Schistosoma species is primarily associated with urinary tract pathology, including bladder cancer?

Schistosoma haematobium.

What is the characteristic feature of a Schistosoma mansoni egg? (image)

A prominent lateral spine.

What is the characteristic feature of a Schistosoma haematobium egg? (image)

A terminal spine.

How is Paragonimus westermani (lung fluke) infection acquired?

Ingestion of metacercariae in raw or undercooked crabs or crayfish.

What is the specimen of choice for diagnosing Paragonimus westermani?

Sputum (or feces if eggs are swallowed).

How are most hermaphroditic fluke infections (e.g., Clonorchis, Fasciola) acquired?

Ingestion of metacercariae in an intermediate host (fish or aquatic plants).

What is a key morphological difference between adult Cestodes and Trematodes?

Cestodes are segmented (proglottids); Trematodes are unsegmented and leaf-shaped.

Do Cestodes (tapeworms) have a digestive tract?

No, they absorb nutrients through their integument.

What is the term for the head or attachment organ of a tapeworm?

Scolex.

What is the term for the segments that make up the body of a tapeworm?

Proglottids.

What is the common term for Trematodes?

Flukes.

What is the common term for Cestodes?

Tapeworms.

What is the common term for Nematodes?

Roundworms.

What is a key characteristic of the phylum Platyhelminthes (flatworms)?

They are dorsoventrally flattened and lack a true body cavity.

What is the recommended staining method for identifying coccidian oocysts like Cryptosporidium?

Modified acid-fast stain.

What is a characteristic feature of Cryptosporidium oocysts? (image)

Small (4-6 µm), round, and stain pink/red with modified acid-fast stain.

How does the development of drug resistance affect diseases like malaria?

It complicates treatment, can lead to treatment failure, and requires the development of new drugs and strategies.

How can immunosuppression affect a parasitic infection?

It can lead to more severe, disseminated disease and reactivation of latent infections.

What is the major class of medically important arthropods with three body regions and six legs?

Insecta.

What is the major class of medically important arthropods with two body regions and eight legs?

Arachnida.

What is the function of an arthropod vector?

It transmits a pathogen (like a parasite) from one host to another.

What is the purpose of calibrating an ocular micrometer?

To make accurate measurements of parasites for identification.

What is the proper way to dispose of contaminated laboratory materials?

Follow institutional biosafety protocols, often involving autoclaving or incineration.

What is the common name for Enterobius vermicularis?

Pinworm.

What is the common name for Trichuris trichiura?

Whipworm.

What is the common name for Ascaris lumbricoides?

Giant intestinal roundworm.

What is the common name for Necator americanus?

New World hookworm.

What is the common name for Ancylostoma duodenale?

Old World hookworm.

What is the common name for Strongyloides stercoralis?

Threadworm.

What is the common name for Taenia saginata?

Beef tapeworm.

What is the common name for Taenia solium?

Pork tapeworm.

What is the common name for Hymenolepis nana?

Dwarf tapeworm.

What is the common name for Clonorchis sinensis?

Chinese liver fluke.

What is the common name for Paragonimus westermani?

Lung fluke.

What is the common name for Fasciola hepatica?

Sheep liver fluke.

What is the causative agent of Chagas' disease?

Trypanosoma cruzi.

What is the causative agent of African Sleeping Sickness?

Trypanosoma brucei (gambiense or rhodesiense).

What is the causative agent of River Blindness?

Onchocerca volvulus.

What is the causative agent of elephantiasis?

Filarial worms, primarily Wuchereria bancrofti.

What disease is caused by Giardia lamblia?

Giardiasis.

What disease is caused by Trichomonas vaginalis?

Trichomoniasis.

What is a potential source of error if a fecal specimen is not fresh or preserved correctly?

Motile trophozoites may die and disintegrate.

What is the primary staining technique for blood smears in parasitology?

Giemsa stain.

What media is used for the culture of free-living amebae like Acanthamoeba?

Non-nutrient agar with a bacterial overlay.