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.