Nematodes

Which species cause lymphatic filariasis?

Wuchereria bancrofti

What species causes river blindness?

Onchocerca volvulus

Course of infection: Wuchereria bancrofti

An infected Aedes mosquito introduces 3L onto the skin where they penetrate into the bite wound.

They develop in adults that reside in the lymphatics in bottom half of body.

After reproduction, adults release sheathed microfilariae that have nocturnal periodicity (10 pm-2 am).

The microfilariae migrate into lymph and blood channels.

Pathology is caused by inflammatory response and length/intensity of exposure to L3 larvae.

In the asymptomatic phase, high microfilaremia can cause lymphatic inflammation and fever.

In the acute phase, antigens from adult worms, Wolbachia, and bacteria from skin can cause intense lymphatic inflammation.

In the chronic phase, blockage of lymph ducts can cause chyluria and elephantiasis.

Diagnose by PCR test to detect parasite DNA or card agglutination test to detect microfilarial antigens.

Treat with ivermectin/albendazole/diethylcarbamazine

What are the types of fluid that can build up in the testicles in the acute phase of infection with W. bancrofti?

Hydrocele, which is a clear fluid.

Chylocele, which is a milky fluid.

Hosts: Wuchereria bancrofti

DH: Humans

IH: Aedes Mosquitoes

Epidemiology: W. bancrofti

Can be found in India, many species of vectors, mass drug administration programs, and prevention can happen by protection against mosquitoes.

Course of infection: Onchocerca volvulus

A Simulium blackfly introduces 3L onto the skin, where they penetrate into the bite wound

In subcutaneous tissues the larvae develop into adults, which reside in subcutaneous nodules.

After reproduction, the females release unsheathed microfilariae. 

Microfilariae migrate and are found in the skin and in the lymphatics of connective tissues.

The adult worms cause onchocercomas and enlarged lymph nodes that cause hanging groin.

The dead microfilariae cause dermatitis which leads to bacterial infections and aging, and if in eye, can cause blindness and inflammation of the cornea.

Diagnose by snipping a piece of nodule and looking for microfilariae/adult worms.

Treat with ivermectin and surgical removal of adults.

Epidemiology: Onchocerca volvulus

Can be found in Nigeria, vector control: controlling black fly populations hard (no pesticides in river or in dense vegetation).

Last 20 years, program to control onchocerciasis.

Hosts: Onchocerca volvulus

DHs: Humans

IHs: Simulium blackflies

Course of Infection: Trichuris trichiura

A host ingests an embryonated egg from feces contaminated hands or food.

In the small intestine, the eggs hatch and release larvae which penetrate the villi.

After a few days, the larvae travel through the tissue to the large intestine and mature into adults.

After reproduction, the posterior end of females sticks into the large intestine and deposits unembryonated eggs.

The eggs are then passed with the feces.

Due to the invasion of the mucosa and wandering, there can be damage, edema, inflammation, and bleeding.

The infection is mostly asymptomatic, but dysentery, anemia, prolapses, and growth retardation in children can occur.

You diagnose by taking a fecal sample and looking for eggs.

Treatment with mebendazole.

Epidemiology: Trichuris trichiura

Most prevalent in tropical countries (India), method and manner of waste disposal, and children most infected.

Hosts: Trichuris trichiura

DHs: Humans

RHs: Primates

Course of Infection: Trichinella spiralis

The host ingests encysted larva from undercooked meat (pork).

In the small intestine, the larvae are released and burrow into the mucosa.

They mature into adults, reproduce, and the larvae are released.

The larvae travel through the circulation to striated muscle and encyst.

The cells are turned into nurse cells and the larvae go dormant.

Adults can cause damage, and inflammation to the intestinal mucosa, leading to vomiting, diarrhea, and cramps.

The migration of the larvae causes damage blood vessels, edema, weakness of infected muscles, and inflammation, leading to fever, myalgia, eosinophilia, and illness specific to the muscle infected.

You diagnose by serodiagnosis or muscle biopsy.

Treat with albendazole.

Epidemiology: Trichinella spiralis

Found mostly in temperate zones (USA), bear meat.

Hosts: Trichinella spiralis

DHs: Humans

IHs: Pigs, rats, bears

Course of Infection: Ascaris lumbricoides

Infection from ingestion of embryonated eggs.

Once in the small intestine, the larvae hatch and penetrate through the mucosa.

They migrate through the circulation into the lungs and mature.

They then penetrate the walls, migrate up the throat, and are swallowed.

In the small intestine, they develop into adult worms, and reproduce.

Eggs are passed with the feces.

The larvae cause damage to the intestinal and lung walls, causing pain and blood.

Wandering adult worms can cause occlusion of the bile tract and appendicitis.

A high burden can cause obstruction.

You can get diagnosed by finding eggs in the feces.

You can get treated with mebendazole.

Epidemiology: Ascaris lumbricoides

Can be found in India, reinfection frequent, cockroaches and wind can carry eggs, eggs can live for years.

Hosts: Ascaris lumbricoides

DHs: Humans

RHs: Pigs

Course of Infection: Enterobius vermicularis

Infection by ingestion of embryonated eggs from hands or environment.

The larvae hatch in the small intestine and mature.

The adults establish themselves in the colon (cecum).

After reproduction, gravid females migrate nocturnally outside the anus and lay eggs on the anal skin.

Retroinfection can occur from the eggs hatching and crawling back into the anus.

Mostly asymptomatic, but anal itching, abdominal pain, and insomnia are common.

Can be diagnosed by the “scotch tape test” and finding eggs.

Treatment by mebendazole.

Epidemiology: Enterobius vermicularis

Highly contagious, can be picked up by wind, can be found in the U.S.

Hosts: Enterobius vermicularis

DHs: Humans

Course of Infection: Necator americanus

Infection by contact of 3L with skin (feet) and the larvae penetrate the skin.

They are then carried through circulation to the heart and then the lungs.

They penetrate the alveoli, migrate up the throat, and are swallowed.

Once in the small intestine, they mature into adults.

Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall and eat blood.

After reproduction, eggs are passed in feces.

Pathology and symptoms based on health and burden (100+).

Cutaneous stage causes ground itch.

Pulmonary stage is mostly asymptomatic but can cause hemorrhaging, cough, and sore throat.

Intestinal phase can cause abdominal pain, loss of appetite, geophagy, and anemia.

You can be diagnosed by finding eggs in feces.

Treatment with Mebendazole.

Epidemiology: Necator americanus

Can be found in U.S., 95% of infections, warm moist environments, caucasians more affected.

Hosts: Necator americanus

DHs: Humans

Course of Infection: Ancylostoma duodenale

Infection by contact of 3L with skin (feet) and the larvae penetrate the skin.

Some can become dormant in muscle, but most are then carried through circulation to the heart and then the lungs.

They penetrate the alveoli, migrate up the throat, and are swallowed.

Once in the small intestine, they mature into adults.

Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall and eat blood.

After reproduction, eggs are passed in feces.

Pathology and symptoms based on health and burden (100+).

Cutaneous stage causes gorund itch.

Pulmonary stage is mostly asymptomatic but can cause hemorrhaging, cough, and sore throat.

Intestinal phase can cause abdominal pain, loss of appetite, geophagy, and anemia.

You can be diagnosed by finding eggs in feces.

Treatment with Mebendazole.

Epidemiology: Ancylostoma duodenale

Can be found in U.S., 5% of infections, warm moist environments, caucasians more affected, reactivation of dormant larvae.

Hosts: Ancylostoma duodenale

DHs: Humans

Course of Infection: Visceral Larval Migrans/Toxocara canis

Infection from ingestion of embryonated eggs from environment or food.

In the small intestine, the larvae are released and penetrate the wall.

Using the circulation, they migrate to various organ tissue and stop development.

The liver and brain are most affected.

The larvae can cause inflammation, granulomas, hepatosplenomegaly, fever, myalgia, meningoencephalitis in the CNS, and pulmonary symptoms.

The damage depends on the number of larvae and site.

ELISA can be used to diagnose.

Albendazole as treatment.

Hosts: Toxocara canis

DHs: Canids

PHs: Humans

Epidemiology: Toxocara canis

Most common in children, can be found in U.S.

Course of Infection: Cutaneous Larval Migrans/hookworm in dogs and cats

Infection from larvae penetrating the skin.

These larvae migrate under the skin.

This causes creeping eruption (itching red lines), and inflammation.

Diagnosed by appearance of creeping eruption.

Treated with albendazole.

Hosts: Cutaneous Larva Migrans

DHs: Dogs and cats

PHs: Humans

Epidemiology: Cutaneous Larva Migrans

Can be found in the U.S., tropical.