Hookworm Infection and Epidemiology

Hookworm

• 1.2 billion infections occur each year, with 100 million being symptomatic.
• There are two parasites that cause hookworm infections, which are found worldwide: Necator americanus and Ancylostoma duodenale.
• Necator americanus is the predominant species in sub-Saharan Africa, south Asia, and the Pacific.
• Ancylostoma duodenale is the predominant species in S.Europe, N.Africa, western Asia, northern China, Japan, and the west coast of America.

Life Cycle

• Adult worms live in the intestine and excrete eggs in the faeces.
• Eggs contaminate soil and develop in warm, damp conditions.
• Eggs hatch and infective filariform larvae develop in about one week and remain infective in soil for many weeks.
• Filariform larvae penetrate the skin when a person walks barefoot in the soil.
• Larvae migrate from the skin to the lungs via the lymphatic and blood systems.
• Larvae penetrate the capillary wall to enter the alveolus.
• Larvae are propelled up the respiratory tree to the epiglottis where they are swallowed.
• They develop to adult stage in the upper intestine, which takes about 5 weeks.
• Eggs are excreted in the faeces.

Pathology

• Hookworms move several times a day to different attachment sites in the upper intestinal mucosa to ingest blood.
• They secrete an anticoagulant, which causes the old attachment sites to continue to bleed.
• Heavy hookworm infection results in chronic haemorrhage from the duodenal and jejunal mucosa.
• The combination of constant blood loss due to hookworm infection and poor iron intake in the diet results in iron deficiency anaemia.
• A. duodenale ingests 4-5 times more blood each day than N. americanus.
• In a child, the continued daily loss of 10ml of blood can lead to severe anaemia.

Lymphatic Filariasis

• 120 million people are infected in >80 countries in Africa, Asia, the Pacific islands, and South and Central America.
• 40 million of those infected are disfigured or severely incapacitated.
• 95% of cases are due to Wuchereria bancrofti, while other species include Brugia malayi and Brugia timori.

Life Cycle

• Wuchereria bancrofti is mainly transmitted by Culex mosquitoes in India and Anopheline mosquitoes in Africa.
• B. malayi and B. timori are transmitted mainly by Mansonia mosquitoes.
• Larval forms of the parasite (microfilariae) are taken up by a female mosquito when it takes a blood meal from a human infected with adult worms.
• The microfilariae develop inside the mosquito.
• When the mosquito takes another blood meal, the infective filariform larvae enter the bite wound.
• Filariform larvae migrate to the lymphatics and lymph glands.
• Larvae develop into sexually mature adult worms over 3-12 months depending on the species of filarial worm.

Symptoms and Signs

• There are three stages of lymphatic filariasis: asymptomatic, acute, and chronic.
• Asymptomatic stage: internal damage to the lymphatics and kidneys.
• Acute stage (filarial lymphangitis): characterized by bouts of fever, heat, redness, pain, swelling, and tenderness of the lymph nodes and ducts.
• Chronic stage: usually results in elephantiasis as a result of chronic lymphoedema, leading to severe deformities.