Overview of Parasitic Infections: Parasitic Infections: Merck Manual Home Edition

Other Parasites
Geographic Area	Source	Common Symptoms	Diagnosis	Treatment
Dog heartworm (Dirofilaria species)
Worldwide (but rare in people)	Larvae are transmitted to people through the bite of infected mosquitoes.	Usually, no symptoms Occasionally, chest pain, cough, and blood in phlegm (sputum) Rarely, nodules under the skin, swelling of the face or eyelid, and a change in vision	Biopsy of lung tissue	None needed
Dwarf tapeworm (Hymenolepis nana)
Worldwide	Eggs may be ingested in food or water contaminated by human feces or may be transferred to the mouth after contact with infected people. Or infected insects, such as fleas and beetles, may be ingested accidentally (for example, in insect-infested grains).	Nausea, vomiting, diarrhea, abdominal discomfort, and weight loss in children with a severe infection	Stool tests	Praziquantel
Echinococcus species (a tapeworm)
Areas of the world where sheep or cattle are raised, as in the Mediterranean, Middle East, Australia, South Africa, and South America, and in areas of Canada, Alaska, California, and Midwestern United States	Eggs excreted in the feces of infected dogs or wild carnivores may be transferred from the hands to the mouth after touching the animal's fur or be ingested in contaminated food.	Abdominal pain and jaundice if the liver is involved Chest pain and coughing up blood or the contents of cysts if the lungs are involved Hives or a severe life-threatening allergic reaction (anaphylaxis)	CT, ultrasonography, or MRI of the liver Sometimes withdrawal of fluid from a cyst in the liver Chest x-ray or CT of the lungs	Albendazole alone or with surgical removal of cysts or Drainage of the cyst with a needle guided by ultrasonography, followed by injection, then removal of a salt solution to kill the parasites in the cyst (percutaneous aspiration-injection-reaspiration)
Intestinal flukes
Most common in the Far East	Flukes on aquatic plants (such as water chestnuts) or in raw or undercooked freshwater fish are ingested.	Usually no symptoms, but with severe infections, abdominal pain, diarrhea, and fever	Stool tests	Praziquantel
Liver flukes (Clonorchis sinensis)
The Far East	Fluke cysts are ingested in raw, dried, salted, or pickled freshwater fish.	Abdominal pain, jaundice, diarrhea, and, years later, cancer of the biliary tract	Stool tests and sometimes colonoscopy	Praziquantel If the biliary tract is blocked, surgery
Loa loa (a filarial worm)
Rain forest belt of western and central Africa	Larvae are transmitted to people through the bite of infected tabanid flies (such as horseflies and deerflies).	Itchy, red areas of swelling (most commonly on the wrists and ankles) and awareness of worms passing across the eye but no eye damage	Blood tests	Diethylcarbamazine (DEC)
Lung flukes (Paragonimus westermani)
Most common in the Far East	Cysts in raw, pickled, or undercooked freshwater crabs and crayfish are ingested.	Difficulty breathing, cough, chest pain, and coughing up blood	Sputum or stool tests, chest x-ray or chest CT, and blood tests	Praziquantel
Sheep liver fluke (Fasciola hepatica)
Areas of the world where sheep or cattle are raised, including Bolivia, Peru, Portugal, France, Iran, Egypt, and Asia	Flukes on watercress or other water plants contaminated by sheep or cattle feces are ingested.	Abdominal pain, fever, fatigue, vague discomfort (malaise), and weight loss due to liver damage	Stool tests and CT, ultrasonography, or MRI of the liver	Bithionol or triclabendazole
Strongyloides stercoralis, or threadworm (a roundworm)
Moist subtropics and tropics and the southeastern United States	Larvae in stool (feces) contaminate the soil and enter through the skin, usually the feet.	Abdominal pain, diarrhea, nausea, vomiting, hives or a rash that changes location, wheezing, and asthma	Stool tests, blood tests, and sometimes colonoscopy If infection is severe and widespread, sputum testing	Ivermectin or albendazole
Trypanosoma brucei gambiense, mainly in West Africa, and Trypanosoma brucei rhodesiense, mainly in East Africa (protozoa that cause African sleeping sickness)
Parts of equatorial Africa	Protozoa are injected through the skin when tsetse flies bite.	Painful bump at the bite site, followed by fever, headache, rash, enlarged lymph nodes, and, eventually (when the brain and spinal fluid are infected), sleepiness, difficulty walking, coma, and, if untreated, ultimately death (infection progresses over many months in West African disease but within weeks in East African disease)	Blood tests and spinal tap	West African sleeping sickness: Eflornithine or the same drugs used to treat East African sleeping sickness East African sleeping sickness: Suramin, pentamidine, or melarsoprol (if the brain and spinal fluid are infected)
Trypanosoma cruzi (protozoa that cause Chagas' disease)
North, Central, and South America	While biting a person, Triatomine bugs (kissing or assassin bugs) defecate, depositing the protozoa in their feces. The protozoa enter through the bug's bite wound, penetrate mucous membranes, or are rubbed into the eyes. The protozoa are sometimes transmitted through blood transfusions or organ transplants or from a pregnant woman to her fetus.	Initially, rash or swelling at the point of entry, swelling around one eye, generalized weakness, and rare but potentially fatal heart or brain infection Years later, long-term heart and gastrointestinal problems	Blood tests	Nifurtimox (United States) or benznidazole (Latin America)
Wuchereria bancrofti, Brugia malayi, and Brugia timori (worms that cause lymphatic filariasis)
Tropical and subtropical areas worldwide	Larvae are transmitted to people through the bite of infected mosquitoes.	Fever, swollen lymph nodes in the groin and armpits, swelling and pain in the groin and limbs, and bacterial infections	Blood tests, including for Wuchereria bancrofti only, and antigen testing	Diethylcarbamazine (DEC) alone or with doxycycline Antibiotics to treat coexisting bacterial skin infections Local measures (such as elevation and an elastic bandage) to reduce swelling (edema)
CT = computed tomography; MRI = magnetic resonance imaging.

Other Parasites

Geographic Area

Source

Common Symptoms

Diagnosis

Treatment

Dog heartworm (Dirofilaria species)
Worldwide (but rare in people)	Larvae are transmitted to people through the bite of infected mosquitoes.	Usually, no symptoms Occasionally, chest pain, cough, and blood in phlegm (sputum) Rarely, nodules under the skin, swelling of the face or eyelid, and a change in vision	Biopsy of lung tissue	None needed
Dwarf tapeworm (Hymenolepis nana)
Worldwide	Eggs may be ingested in food or water contaminated by human feces or may be transferred to the mouth after contact with infected people. Or infected insects, such as fleas and beetles, may be ingested accidentally (for example, in insect-infested grains).	Nausea, vomiting, diarrhea, abdominal discomfort, and weight loss in children with a severe infection	Stool tests	Praziquantel
Echinococcus species (a tapeworm)
Areas of the world where sheep or cattle are raised, as in the Mediterranean, Middle East, Australia, South Africa, and South America, and in areas of Canada, Alaska, California, and Midwestern United States	Eggs excreted in the feces of infected dogs or wild carnivores may be transferred from the hands to the mouth after touching the animal's fur or be ingested in contaminated food.	Abdominal pain and jaundice if the liver is involved Chest pain and coughing up blood or the contents of cysts if the lungs are involved Hives or a severe life-threatening allergic reaction (anaphylaxis)	CT, ultrasonography, or MRI of the liver Sometimes withdrawal of fluid from a cyst in the liver Chest x-ray or CT of the lungs	Albendazole alone or with surgical removal of cysts or Drainage of the cyst with a needle guided by ultrasonography, followed by injection, then removal of a salt solution to kill the parasites in the cyst (percutaneous aspiration-injection-reaspiration)
Intestinal flukes
Most common in the Far East	Flukes on aquatic plants (such as water chestnuts) or in raw or undercooked freshwater fish are ingested.	Usually no symptoms, but with severe infections, abdominal pain, diarrhea, and fever	Stool tests	Praziquantel
Liver flukes (Clonorchis sinensis)
The Far East	Fluke cysts are ingested in raw, dried, salted, or pickled freshwater fish.	Abdominal pain, jaundice, diarrhea, and, years later, cancer of the biliary tract	Stool tests and sometimes colonoscopy	Praziquantel If the biliary tract is blocked, surgery
Loa loa (a filarial worm)
Rain forest belt of western and central Africa	Larvae are transmitted to people through the bite of infected tabanid flies (such as horseflies and deerflies).	Itchy, red areas of swelling (most commonly on the wrists and ankles) and awareness of worms passing across the eye but no eye damage	Blood tests	Diethylcarbamazine (DEC)
Lung flukes (Paragonimus westermani)
Most common in the Far East	Cysts in raw, pickled, or undercooked freshwater crabs and crayfish are ingested.	Difficulty breathing, cough, chest pain, and coughing up blood	Sputum or stool tests, chest x-ray or chest CT, and blood tests	Praziquantel
Sheep liver fluke (Fasciola hepatica)
Areas of the world where sheep or cattle are raised, including Bolivia, Peru, Portugal, France, Iran, Egypt, and Asia	Flukes on watercress or other water plants contaminated by sheep or cattle feces are ingested.	Abdominal pain, fever, fatigue, vague discomfort (malaise), and weight loss due to liver damage	Stool tests and CT, ultrasonography, or MRI of the liver	Bithionol or triclabendazole
Strongyloides stercoralis, or threadworm (a roundworm)
Moist subtropics and tropics and the southeastern United States	Larvae in stool (feces) contaminate the soil and enter through the skin, usually the feet.	Abdominal pain, diarrhea, nausea, vomiting, hives or a rash that changes location, wheezing, and asthma	Stool tests, blood tests, and sometimes colonoscopy If infection is severe and widespread, sputum testing	Ivermectin or albendazole
Trypanosoma brucei gambiense, mainly in West Africa, and Trypanosoma brucei rhodesiense, mainly in East Africa (protozoa that cause African sleeping sickness)
Parts of equatorial Africa	Protozoa are injected through the skin when tsetse flies bite.	Painful bump at the bite site, followed by fever, headache, rash, enlarged lymph nodes, and, eventually (when the brain and spinal fluid are infected), sleepiness, difficulty walking, coma, and, if untreated, ultimately death (infection progresses over many months in West African disease but within weeks in East African disease)	Blood tests and spinal tap	West African sleeping sickness: Eflornithine or the same drugs used to treat East African sleeping sickness East African sleeping sickness: Suramin, pentamidine, or melarsoprol (if the brain and spinal fluid are infected)
Trypanosoma cruzi (protozoa that cause Chagas' disease)
North, Central, and South America	While biting a person, Triatomine bugs (kissing or assassin bugs) defecate, depositing the protozoa in their feces. The protozoa enter through the bug's bite wound, penetrate mucous membranes, or are rubbed into the eyes. The protozoa are sometimes transmitted through blood transfusions or organ transplants or from a pregnant woman to her fetus.	Initially, rash or swelling at the point of entry, swelling around one eye, generalized weakness, and rare but potentially fatal heart or brain infection Years later, long-term heart and gastrointestinal problems	Blood tests	Nifurtimox (United States) or benznidazole (Latin America)
Wuchereria bancrofti, Brugia malayi, and Brugia timori (worms that cause lymphatic filariasis)
Tropical and subtropical areas worldwide	Larvae are transmitted to people through the bite of infected mosquitoes.	Fever, swollen lymph nodes in the groin and armpits, swelling and pain in the groin and limbs, and bacterial infections	Blood tests, including for Wuchereria bancrofti only, and antigen testing	Diethylcarbamazine (DEC) alone or with doxycycline Antibiotics to treat coexisting bacterial skin infections Local measures (such as elevation and an elastic bandage) to reduce swelling (edema)
CT = computed tomography; MRI = magnetic resonance imaging.