Parasitology

 

Protozoa:

Plasmodium:

• Habitat: Human red blood cells (RBCs).
• Morphology:

• Trophozoite: Amoeboid shape, 1-2 micrometers.
• Merozoite: Small, ring-shaped form, 1-2 micrometers.
• Gametocyte: Larger than trophozoite, crescent or round shape.

• Life Cycle: Mosquito (Anopheles) acts as a vector; transmission through sporozoites. Involves liver (exoerythrocytic) and blood (erythrocytic) stages.
• Pathogenesis: Causes malaria with symptoms such as fever, chills, and anemia. Severe cases may lead to organ dysfunction and death.
• Lab Diagnosis:

• Blood smear examination (Giemsa stain): Identifies stages in RBCs.
• Rapid diagnostic tests (RDTs): Detects specific antigens (histidine-rich protein 2).
• Molecular methods like PCR: For species identification.

Giardia lamblia:

• Habitat: Human small intestine.
• Morphology:

• Trophozoite: Pear-shaped, 10-20 micrometers.
• Cyst: Oval, 8-12 micrometers, with four nuclei and cyst wall.

• Life Cycle: Fecal-oral transmission. Cysts are ingested from contaminated water or food.
• Pathogenesis: Causes giardiasis with symptoms like diarrhea, abdominal cramps, and malabsorption.
• Lab Diagnosis:

• Microscopy (direct wet mount or stained preparations): Identifies trophozoites and cysts.
• ELISA for antigen detection: Detects Giardia-specific antigens.
• PCR for molecular identification: Provides species-level identification.

Entamoeba histolytica:

• Habitat: Human colon.
• Morphology:

• Trophozoite: Amoeboid shape, 10-60 micrometers, with ingested RBCs.
• Cyst: Round, 10-20 micrometers, with four nuclei and a chromatoid body.

• Life Cycle: Fecal-oral transmission. Cysts are ingested, releasing trophozoites in the colon.
• Pathogenesis: Causes amebiasis with symptoms like dysentery, liver abscess, and colitis.
• Lab Diagnosis:

• Microscopy (fresh stool or stained smears): Identifies trophozoites and cysts.
• Antigen detection tests (ELISA): Detects specific antigens.
• Molecular methods like PCR: For differentiation from non-pathogenic species.

Toxoplasma gondii:

• Habitat: Intracellular in mammals.
• Morphology:

• Tachyzoite: Crescent-shaped, 4-7 micrometers.
• Cyst: Spherical structure containing bradyzoites.

• Life Cycle: Cats are definitive hosts; transmission through ingestion of oocysts or tissue cysts.
• Pathogenesis: Causes toxoplasmosis, often asymptomatic but can be severe in immunocompromised individuals. Congenital infection can lead to birth defects.
• Lab Diagnosis:

• Serology (IgM and IgG antibody detection): Detects antibodies against T. gondii.
• PCR for DNA detection: Identifies genetic material.
• Histopathological examination: Detects tissue cysts.

Leishmania spp.:

• Habitat: Intracellular in macrophages.
• Morphology:

• Amastigote: Oval shape within host cells.
• Promastigote: Elongated with flagellum, 10-20 micrometers.

• Life Cycle: Sandflies (Phlebotomus and Lutzomyia) act as vectors; transmission through promastigotes during a blood meal.
• Pathogenesis: Causes leishmaniasis with various clinical manifestations (cutaneous, mucocutaneous, visceral). Disseminated visceral forms can be fatal.
• Lab Diagnosis:

• Microscopic examination of smears: Identifies amastigotes in tissues and promastigotes in culture.
• Serology (antibody detection): Detects anti-Leishmania antibodies.
• Molecular methods like PCR: For species identification.

Trypanosoma cruzi:

• Habitat: Intracellular in blood and tissues.
• Morphology:

• Amastigote: Oval shape within host cells.
• Epimastigote: Elongated with a kinetoplast.
• Trypomastigote: Pear-shaped with a flagellum.

• Life Cycle: Triatomine bugs (kissing bugs) act as vectors; transmission through feces entering the bloodstream. Can also occur through blood transfusions or congenital transmission.
• Pathogenesis: Causes Chagas disease with acute and chronic phases, leading to heart and digestive system complications.
• Lab Diagnosis:

• Microscopic examination of blood smears: Identifies trypomastigotes.
• Serology (antibody detection): Detects anti-T. cruzi antibodies.
• Molecular methods like PCR: For species identification.

Cryptosporidium parvum:

• Habitat: Microvilli of the small intestine.
• Morphology:

• Oocyst: Round, 4-6 micrometers, containing four sporozoites.

• Life Cycle: Fecal-oral transmission through oocysts. Resistant to chlorine disinfection.
• Pathogenesis: Causes cryptosporidiosis with symptoms like watery diarrhea, abdominal cramps, and weight loss.
• Lab Diagnosis:

• Modified acid-fast stain: Identifies oocysts in stool.
• Antigen detection tests (ELISA): Detects Cryptosporidium-specific antigens.
• PCR for molecular identification: Provides species-level identification.

Entamoeba coli:

• Habitat: Human colon.
• Morphology:

• Trophozoite: Large, non-pathogenic amoeba.
• Cyst: Similar to E. histolytica cyst but non-pathogenic.

• Life Cycle: Fecal-oral transmission. Considered non-pathogenic.
• Pathogenesis: Generally non-pathogenic, may cause mild gastrointestinal symptoms.
• Lab Diagnosis:

• Microscopy (fresh stool or stained smears): Identifies trophozoites and cysts.
• Antigen detection tests (ELISA): Limited availability due to non-pathogenic nature.
• Molecular methods like PCR: For differentiation from E. histolytica.

Balantidium coli:

• Habitat: Human colon.
• Morphology:

• Trophozoite: Largest protozoan, ciliated with a kidney-shaped macronucleus.
• Cyst: Oval, 50-70 micrometers, with a thick cyst wall.

• Life Cycle: Fecal-oral transmission. Pigs serve as reservoir hosts.
• Pathogenesis: Causes balantidiasis with symptoms like dysentery and abdominal pain.
• Lab Diagnosis:

• Microscopy (fresh stool or stained smears): Identifies trophozoites and cysts.
• Serology: Limited availability.
• Molecular methods like PCR: For species identification.

Cyclospora cayetanensis:

• Habitat: Epithelial cells of the small intestine.
• Morphology:

• Oocyst: Round, 8-10 micrometers, containing two sporocysts.

• Life Cycle: Fecal-oral transmission through oocysts. Associated with contaminated food and water.
• Pathogenesis: Causes cyclosporiasis with symptoms like watery diarrhea, abdominal cramps, and fatigue.
• Lab Diagnosis:

• Modified acid-fast stain: Identifies oocysts in stool.
• Antigen detection tests (ELISA): Detects Cyclospora-specific antigens.
• PCR for molecular identification: Provides species-level identification.

 

Nematodes:

Ascaris lumbricoides:

• Habitat: Small intestine.
• Morphology:

• Adult Male/Female: Large, cylindrical worms. Females: 20-35 cm; Males: 15-30 cm.
• Egg: Oval-shaped, thick-shelled with a mammillated surface.

• Life Cycle: Fecal-oral transmission. Eggs are ingested, and larvae migrate through tissues.
• Pathogenesis: Ascarisiasis with symptoms like intestinal obstruction, malnutrition, and respiratory issues.
• Lab Diagnosis:

• Microscopy (eggs in stool): Identifies characteristic eggs.
• Serology for antibody detection: May indicate recent or current infection.
• Molecular methods for species identification: Differentiates from other Ascaris species.

Hookworms (Ancylostoma, Necator):

• Habitat: Small intestine.
• Morphology:

• Adult Male/Female: Small, hook-like mouthparts. Females: 1 cm; Males: 0.5 cm.
• Egg: Oval-shaped with a thin shell.

• Life Cycle: Skin penetration and fecal-oral transmission. Larvae migrate through the skin, and adults attach to the intestinal mucosa.
• Pathogenesis: Hookworm infection with symptoms including anemia, iron deficiency, and gastrointestinal issues.
• Lab Diagnosis:

• Microscopy (eggs in stool): Identifies characteristic eggs.
• Serology for antibody detection: Indicative of current or recent infection.
• Molecular methods for species identification: Differentiates between Ancylostoma and Necator.

Trichuris trichiura:

• Habitat: Large intestine.
• Morphology:

• Adult Male/Female: Thread-like, whip-shaped worms. Females: 3-5 cm; Males: 2-3 cm.
• Egg: Barrel-shaped with polar plugs.

• Life Cycle: Fecal-oral transmission. Eggs are ingested, and larvae develop in the cecum and colon.
• Pathogenesis: Trichuriasis with symptoms like abdominal pain, bloody diarrhea, and rectal prolapse.
• Lab Diagnosis:

• Microscopy (eggs in stool): Identifies characteristic eggs.
• Serology for antibody detection: May indicate recent or current infection.
• Molecular methods for species identification: Differentiates from other Trichuris species.

Strongyloides stercoralis:

• Habitat: Small intestine.
• Morphology:

• Adult Male/Female: Female worms are parasitic, while males are free-living in soil.
• Larvae: Filariform larvae, 200-400 micrometers.

• Life Cycle: Fecal-oral transmission. Infection can also occur through skin penetration by filariform larvae.
• Pathogenesis: Causes strongyloidiasis with symptoms ranging from mild gastrointestinal to severe disseminated disease, including hyperinfection syndrome.
• Lab Diagnosis:

• Microscopy (larvae in stool, sputum, or duodenal fluid): Identifies characteristic larvae.
• Serology for antibody detection: Indicative of current or past infection.
• Molecular methods for species identification: Differentiates from other Strongyloides species.

Enterobius vermicularis:

• Habitat: Colon.
• Morphology:

• Adult Male/Female: Small, thread-like worms. Females: 8-13 mm; Males: 2-5 mm.
• Egg: Oval-shaped with flattened side, 50-60 micrometers.

• Life Cycle: Fecal-oral transmission, perianal autoinfection. Eggs are ingested, and larvae mature in the cecum.
• Pathogenesis: Enterobiasis with perianal itching.
• Lab Diagnosis:

• Scotch tape test (perianal swab): Collects eggs from the perianal region.
• Microscopy (eggs in perianal swab or fecal sample): Identifies characteristic eggs.
• Molecular methods for species identification: Differentiates from other Enterobius species.

Wuchereria bancrofti (Lymphatic Filariasis):

• Habitat: Lymphatic vessels.
• Morphology:

• Adult Male/Female: Thread-like worms. Females: Up to 10 cm; Males: Up to 5 cm.
• Microfilariae: Microscopic larvae in blood, sheathed.

• Life Cycle: Mosquitoes act as vectors; transmission through infective larvae. Adults reside in lymphatic vessels.
• Pathogenesis: Causes lymphatic filariasis with symptoms like lymphedema, elephantiasis, and hydrocele.
• Lab Diagnosis:

• Microscopy (microfilariae in blood): Identifies sheathed microfilariae.
• Serology for antibody detection: Detects specific antibodies.
• Molecular methods for species identification: Differentiates from other filarial species.

Onchocerca volvulus (Onchocerciasis or River Blindness):

• Habitat: Subcutaneous tissues, nodules.
• Morphology:

• Adult Male/Female: Thread-like worms. Females: Up to 50 cm; Males: Up to 5 cm.
• Microfilariae: Microscopic larvae in skin, unsheathed.

• Life Cycle: Black flies act as vectors; transmission through infective larvae. Adults form nodules in subcutaneous tissues.
• Pathogenesis: Causes onchocerciasis with symptoms like skin changes, visual impairment, and blindness.
• Lab Diagnosis:

• Skin snip biopsy (microfilariae in skin): Identifies unsheathed microfilariae.
• Serology for antibody detection: Detects specific antibodies.
• Molecular methods for species identification: Differentiates from other filarial species.

Loa loa (Loiasis or African Eye Worm):

• Habitat: Subcutaneous tissues.
• Morphology:

• Adult Male/Female: Thread-like worms. Females: Up to 7 cm; Males: Up to 4 cm.
• Microfilariae: Microscopic larvae in blood, sheathed.

• Life Cycle: Deer flies (Chrysops) act as vectors; transmission through infective larvae. Adults migrate in subcutaneous tissues.
• Pathogenesis: Causes loiasis with symptoms like Calabar swellings and migration of adult worms in the eye.
• Lab Diagnosis:

• Microscopy (microfilariae in blood): Identifies sheathed microfilariae.
• Serology for antibody detection: Detects specific antibodies.
• Molecular methods for species identification: Differentiates from other filarial species.

Trematodes:

Schistosoma spp.:

• Habitat: Blood vessels.
• Morphology:

• Adult Male/Female: Flat, elongated worms with a ventral groove. Female: 7-20 mm; Male: 4-15 mm.
• Egg: Oval-shaped with a spine, 120-180 micrometers.

• Life Cycle: Snail intermediate host; cercariae penetrate human skin. Eggs are excreted in feces or urine.
• Pathogenesis: Causes schistosomiasis with symptoms like hepatosplenomegaly, hematuria, and portal hypertension.
• Lab Diagnosis:

• Microscopy (eggs in urine or stool): Identifies characteristic eggs.
• Serology (antibody and antigen detection): Detects antibodies or circulating antigens.
• PCR for species identification: Differentiates between Schistosoma species.

Fasciola hepatica:

• Habitat: Liver, bile ducts.
• Morphology:

• Adult Male/Female: Leaf-shaped, large flukes. Female: 20-30 mm by 8-13 mm; Male: 12-25 mm by 6-13 mm.
• Egg: Oval-shaped, operculated, 130-150 micrometers.

• Life Cycle: Snail intermediate host; metacercariae on vegetation. Humans are infected by ingesting contaminated water or plants.
• Pathogenesis: Causes fascioliasis with symptoms like hepatomegaly, abdominal pain, and jaundice.
• Lab Diagnosis:

• ELISA (detection of antibodies): Identifies specific antibodies.
• Imaging (ultrasound for liver abnormalities): Shows characteristic lesions.
• PCR for species identification: Differentiates from other Fasciola species.

Clonorchis sinensis:

• Habitat: Liver, bile ducts.
• Morphology:

• Adult Male/Female: Leaf-shaped, small flukes. Female: 15-20 mm by 3-5 mm; Male: 10-15 mm by 1-2 mm.
• Egg: Oval-shaped, operculated, 27-35 micrometers by 13-18 micrometers.

• Life Cycle: Snail and fish intermediate hosts; ingestion of raw or undercooked fish. Metacercariae encyst in fish tissues.
• Pathogenesis: Clonorchiasis with symptoms like cholangitis, biliary obstruction, and cholecystitis.
• Lab Diagnosis:

• Microscopy (eggs in stool): Identifies characteristic eggs.
• Imaging (CT/MRI for liver abnormalities): Shows bile duct dilation.
• Serology: Detects specific antibodies.
• PCR for species identification: Differentiates from other Clonorchis species.

Paragonimus spp.:

• Habitat: Lungs.
• Morphology:

• Adult Male/Female: Flattened, small flukes. Female: 7-15 mm by 3-5 mm; Male: 5-10 mm by 2-4 mm.
• Egg: Oval-shaped, operculated, 85-120 micrometers by 50-80 micrometers.

• Life Cycle: Snail and crab intermediate hosts; metacercariae in crab tissues. Humans are infected by ingesting undercooked crab or crayfish.
• Pathogenesis: Paragonimiasis with symptoms like chronic cough, hemoptysis, and chest pain.
• Lab Diagnosis:

• Microscopy (eggs in sputum or feces): Identifies characteristic eggs.
• Imaging (chest X-ray or CT scan): Shows pulmonary lesions.
• Serology: Detects specific antibodies.
• PCR for species identification: Differentiates from other Paragonimus species.

Cestodes:

Taenia solium (Pork Tapeworm):

• Habitat: Small intestine.
• Morphology:

• Adult Male/Female: Elongated, ribbon-like worms. Length can reach several meters.
• Proglottid: Segments containing eggs.
• Egg: Round, 30-40 micrometers.

• Life Cycle: Humans are definitive hosts; ingestion of undercooked pork with cysticerci. Cysts can form in various tissues.
• Pathogenesis: Causes taeniasis with symptoms like abdominal pain and weight loss. Cysticercosis can lead to neurocysticercosis with neurological symptoms.
• Lab Diagnosis:

• Microscopy (eggs or proglottids in stool): Identifies characteristic eggs or proglottids.
• Imaging (CT/MRI for cysticercosis): Detects cysts in tissues.
• Serology: Detects specific antibodies.
• PCR for species identification: Differentiates from other Taenia species.

Echinococcus granulosus (Hydatid Tapeworm):

• Habitat: Small intestine.
• Morphology:

• Adult Male/Female: Small tapeworm, 3-6 mm.
• Hydatid cyst: Large cyst containing protoscolices.

• Life Cycle: Dogs are definitive hosts; ingestion of eggs. Humans can be intermediate hosts with the formation of hydatid cysts in various organs.
• Pathogenesis: Causes cystic echinococcosis with symptoms depending on the involved organ.
• Lab Diagnosis:

• Imaging (ultrasound, CT, or MRI for cysts): Identifies characteristic cysts.
• Serology: Detects specific antibodies.
• PCR for species identification: Differentiates from other Echinococcus species.

Diphyllobothrium latum (Fish Tapeworm):

• Habitat: Small intestine.
• Morphology:

• Adult Male/Female: Long tapeworm, can reach several meters.
• Proglottid: Segments containing eggs.
• Egg: Oval-shaped, operculated, 55-75 micrometers by 40-50 micrometers.

• Life Cycle: Humans are definitive hosts; ingestion of raw or undercooked fish containing plerocercoid larvae.
• Pathogenesis: Causes diphyllobothriasis with symptoms like abdominal discomfort, diarrhea, and vitamin B12 deficiency.
• Lab Diagnosis:

• Microscopy (eggs or proglottids in stool): Identifies characteristic eggs or proglottids.
• Serology: Detects specific antibodies.
• PCR for species identification: Differentiates from other Diphyllobothrium species.

Hymenolepis nana:

• Habitat: Small intestine.
• Morphology:

• Adult: Small tapeworm, 15-40 mm.
• Egg: Oval, with a polar filament.

• Life Cycle: Fecal-oral transmission through contaminated food or water. Direct life cycle without an intermediate host.
• Pathogenesis: Causes hymenolepiasis with symptoms like abdominal pain, diarrhea, and weight loss.
• Lab Diagnosis:

• Microscopy (eggs in stool): Identifies characteristic eggs.

Taenia saginata:

• Habitat: Small intestine of humans (definitive host).
• Morphology:

• Adult: Large tapeworm, 4-10 meters.
• Proglottids: Wide and rectangular, with a central uterine pore.

• Life Cycle: Ingestion of undercooked beef containing cysticerci.
• Pathogenesis: Causes taeniasis with mild or no symptoms.
• Lab Diagnosis:

• Microscopy (proglottids or eggs in stool): Identifies characteristic proglottids and eggs.
• Serology: Detects specific antibodies.

Taenia solium:

• Habitat: Small intestine of humans (definitive host).
• Morphology:

• Adult: Large tapeworm, 2-7 meters.
• Proglottids: Narrower than T. saginata, with a central uterine pore.

• Life Cycle: Ingestion of undercooked pork containing cysticerci. Can also cause cysticercosis if humans ingest eggs from contaminated food or water.
• Pathogenesis:

• Taeniasis: Mild or no symptoms.
• Cysticercosis: Formation of cysticerci in tissues, leading to various symptoms depending on the organ involved.

• Lab Diagnosis:

• Microscopy (proglottids or eggs in stool): Identifies characteristic proglottids and eggs.
• Serology: Detects specific antibodies.

Trematodes (Flukes):

Fasciolopsis buski:

• Habitat: Small intestine.
• Morphology:

• Adult: Large, leaf-shaped fluke, 2-7.5 cm.
• Egg: Ovoid, operculated.

• Life Cycle: Ingestion of aquatic plants containing metacercariae.
• Pathogenesis: Causes fasciolopsiasis with symptoms like abdominal pain, diarrhea, and intestinal obstruction.
• Lab Diagnosis:

• Microscopy (eggs in stool): Identifies characteristic eggs.
• Serology: Detects specific antibodies.

Paragonimus spp.:

• Habitat: Lungs.
• Morphology:

• Adult: Flattened fluke with oral and ventral suckers.
• Egg: Ovoid, operculated.

• Life Cycle: Ingestion of undercooked crustaceans (crabs and crayfish) containing metacercariae.
• Pathogenesis: Causes paragonimiasis with symptoms like chronic cough, hemoptysis, and chest pain.
• Lab Diagnosis:

• Microscopy (eggs in sputum or stool): Identifies characteristic eggs.
• Serology: Detects specific antibodies.

Schistosoma spp.:

• Habitat: Blood vessels.
• Morphology:

• Adult Male/Female: Flat, elongated worms with a ventral groove. Female: 7-20 mm; Male: 4-15 mm.
• Egg: Oval-shaped with a spine, 120-180 micrometers.

• Life Cycle: Snail intermediate host; cercariae penetrate human skin. Eggs are excreted in feces or urine.
• Pathogenesis: Causes schistosomiasis with symptoms like hepatosplenomegaly, hematuria, and portal hypertension.
• Lab Diagnosis:

• Microscopy (eggs in urine or stool): Identifies characteristic eggs.
• Serology (antibody and antigen detection): Detects antibodies or circulating antigens.
• PCR for species identification: Differentiates between Schistosoma species.