Blood and Tissue Nematodes

Lymphatic Filariasis - The Pathogens

• Brugia malayi

• Wuchereria bancrofti

Lymphatic Filariasis - Epidemiology

• vector: various types of mosquitoes; mosquitoes feed primarily during the night

• human and animal reservoirs

Lymphatic Filariasis - Clinical Syndrome

• most infected people are asymptomatic and will never develop clinical symptoms; although the parasite will damage the lymphatic system

• Lymphedema/Elephantiasis

• Pulmonary eosinophilia syndrome

Lymphedema/Elephantiasis

• Fluid collection and swelling (mostly affects the arms/legs, breasts and genitalia)

• secondary bacterial infections in the skin and lymph system which causes hardening and thickening of the skin

Pulmonary eosinophilia syndrome

cough, shortness of breath and wheezing

Life Cycle of Lymphatic Filarial Parasites

• infection occurs through mosquito bite, introduces filarial larvae (infective stage)

• adults (live 5-7 yrs) reside in the lymphatics where they develop microfilariae

• microfilariae migrate to blood (both) (diagnostic stage) or lymph (Wuchereria only)

• mosquito ingests the microfilariae during a blood meal

• microfilariae continue to develop in the mosquito until they reach the third-stage larvae which will migrate to the mosquito’s head/proboscis

Infective Stage of Lymphatic Filariasis

infection occurs through mosquito bite, introduces filarial larvae

Lymphatic Filariasis Diagnostic Stage

blood (both) or lymph (Wuchereria only)

Lymphatic Filariasis - Diagnosis

• Demonstration of microfilariae in the blood

  • Giemsa-stained blood films

  • Microfilariae typically have nocturnal periodicity - blood draw between 10pm and 4am

• Antigen or antibody detection

  • can be detected in the blood samples collected at anytime of day (more meaningful in patients who have not resided in the area for extended periods)

Lymphatic Filariasis - Treatment and Prevention

• Diethylcarbamazine for patients infected with no symptoms

• patients with lymphedema/elpehantiasis are unlikely to benefit from treatment (personal hygiene)

• vector control: wear long sleeves/pants, sleep under nets, use insecticide

Onchocera volvulus - Epidemiology

• distribution: endemic in many parts of Africa; occurs in Central America and South America

  • 99% of infected people live in Africa

• Affects more than 18 million people and causes blindness of those infected

• vector: Simulium damnosum “the damned blackfly”

• human reservoir

Life Cycle of Onchocerca

• infection occurs through blackfly bite, introduces larvae (infective stage)

• in the subcutaneous tissue, the larvae develop into adults (live up to 15 yrs), resides in nodules

• females produce microfilariae (for ~9 years); typically found in the skin (diagnostic stage) or lymphatics

• occasionally, the microfilariae migrate to the blood where the blackfly will take a blood meal and ingests the microfilariae

• microfilariae continue to develop in the blackfly until they reach third-stage larvae which will migrate to the blackfly’s head/proboscis

Infective Stage of Onchocerca

larvae

Diagnostic Stage Onchocera

skin

Onchocerca volvulus - Clinical Syndromes

• 2nd leading infectious cause of blindness in the world

• infection of the skin subcutaneous tissue, lymph nodes and eyes (river blindness)

  • transmission is the most intense in remove African rural agricultural villages, located near rapidly flowing streams

• clinical manifestations result from inflammatory reaction to antigens released by the microfilariae as they migrate through the tissues (and die) - skin rash

Onchocerca volvulus - Diagnosis

• demonstration of microfilariae in skin snip preparations or biopsy of skin nodules

  • no periodicity, so specimen can be taken at anytime

• molecular methods to detect onchocercal DNA in skin snip specimens

Onchocera volvulus - Treatment and Prevention

• ivermectin

• vector control (blackfly bites during the day)

  • wear long sleeves/pants, use insecticide

Loa loa - Epidemiology

• distribution: equatorial rain forests of Africa (endemic in tropical West Africa, the Congo basin, and parts of Nigeria)

• vector: deer flies

• human and animal reservoirs

Life Cycle of Loa loa

• infection occurs through deerfly bite, introduces larvae (infective stage)

• larvae become adults and live in connective tissue/fascia (live up to 17 yrs)

• females produce microfilariae which will be found in the lymph vessels and lungs

• during the day, the microfilariae migrate to the blood (diagnostic stage): where the deerfly will take a blood meal and ingest the microfilariae

• microfilariae continue to develop in the deerfly until they reach the third-stage larvae which will migrate to the deerfly’s head/proboscis

Infective Stage of Loa loa

larvae

Diagnostic stage Loa loa

blood

Loa loa - Clinical Syndromes

• most people are asymptomatic; infections show up many months after

• after ~1 year after infection, see calabar swellings (typically on extremities) (result from allergic reaction to the worm)

• eye worm: visible movement of the adult across the surface of the eye or under the skin

Loa loa - Diagnosis

• clinical observation of Calabar swellings or migration of adult worms in the eye/under the skin

• demonstration of microfilariae in the blood

  • giemsa-stained blood films

  • microfilariae typically have daytime periodicity - blood drawn between 10am and 4pm

Loa loa - Treatment and Prevention

• diethylcarbamazine

• death of the parasites might induce strong allergic reaction (treat with steroids)

• surgical removal of the worms as they migrate across the bridge of nose (can be done to relieve anxiety only - no cure(

• wear long sleeves/pants, insect repellents

Trichinella spiralis - Epidemiology

• worldwide distribution among meat-eating populations (greatest prevalence is associated with the consumption of pork)

  • occurrence in the United States is largely limited to sporadic cases or small clusters related to consumption of home-processed meats from noncommercial farm-raised pigs and wild game

• animal reservoir (many carnivorous and omnivorus animals)

Life Cycle of Trichinella

• infection occurs through ingestion of undercooked meat containing encysted larvae (infective stage)

• after exposure to gastric acid and pepsin, larvae are released from the cysts and invade the small intestine mucosa where they become adults

• females release larvae that migrate to striated muscles (diagnostic stage) where they encyst produce microfilariae which will be found in the lymph vessels and lungs

Infective Stage of Trichinella

encysted larvae

Diagnostic stage Trichinella

striated muscles

Trichinella spiralis - Clinical Syndromes

• initial symptoms are gastrointestinal due to the invasion of the intestinal wall by the juvenile larvae - nausea, diarrhea, vomiting, abdominal pain

• 2 weeks later (can last up to 8 weeks) - with larval migration see fever, weakness, diarrhea, blurred vision, and muscle pain

• in heavy infections, severe neurological, heart and breathing symptoms

Trichinella spiralis - Diagnosis

• clinical observation/ history/ symptoms

• tissue biopsy followed by microscopy or molecular analysis

• antibody detection

Trichinella spiralis - Treatment and Prevention

• early treatment for best results (once larvae are established in muscle, treatment many not eliminate the infection)

• albendazole/mebendazole

• steroids for severe symptoms

• education on the proper cooking of meat (microwave does not kill the larvae)

  • low temperature storage of meat (-15 C) for 20 days or more may destroy the organism

Toxocara - Epidemology

• worldwide distribution

  • global prevalence of antibodies is 19%

  • 5% of US population has antibodies

  • boys usually have the higher seroprevalence

• animal reservoir: intestines of dogs and cats

  • 30% of dogs younger than 6 months; 25% of all cats

Life Cycle of Toxocara

• infection occurs through ingestion of egg or undercooked meat (infective stage)

• eggs hatch and larvae penetrate the intestinal wall and are carried by circulation to a variety of tissues (diagnostic stage)

• humans are accidental hosts; the larvae do not undergo further development

Toxocara - Clinical Syndrome

• toxocariasis usually affects kids under age 10; usually asymptomatic and self-limiting

• visceral larval migrans (VLM)

• ocular larva migrans (OLM)

Visceral larval migrans (VLM)

• some symptoms of VLM are caused by the movement of the worms through the body, include fever, coughing, wheezing; hepatomegaly

• heavier or repeated Toxocara infections, while rare, can cause VLM

Ocular larva migrans (OLM)

• OLM occurs when a microscopic worm enters the eye; it may cause inflammation and formation of a scar on the retina

• lack of the fever and respiratory symptoms

Toxocara - Diagnosis

• diagnosis of VLM and OLM is based on clinical findings, the presence of eosinophilia, and known exposure to dogs, cats, or raccoons

• antibody detection

• examination of fecal material from infected pets often supports the diagnosis

Toxocara - Treatment and Prevention

• albendazole/mebendazole

• steroids to control inflammation in the eye

• antiparasitic treatment of animals

• education and wash hands

  • do not allow children to play in areas that are soiled by animals; cover sandboxes when not in use