Helminth infestation

Non-intestinal

Filariasis
The adult worms are threadlike. The large females give birth to larvae known as microfilaria. These require two hosts to complete their lifecycle. The first host is the mosquito culex, aedes, anopheles or other types of flies such as Simulium.

Clinical features Wuchereria bancrofti
Adult worms are found in the lymphatics and lymph nodes. Larvae grow and mature in the regional lymph nodes for up to 18 months. The patient then presents with fever ranging 39° - 41°C accompanied by lymphangitis, both of which subside in 3 - 5 days. The involved lymphatics appear as red streaks on the skin, are tender and cord-like. The lymphatics of the epididymis, testes and spermatic cord may be involved. The obstruction phase follows if treatment is not given. This presents with oedema of the lower limbs and scrota. Long-standing oedema produces thick rough skin which may ulcerate.

Complications -  Tropical eosinophilia is characterized by either lymphadenopathy, splenomegaly or cough, bronchospasm and asthma-like picture.

Loa loa
Clinical features are caused by adult worms which prefer the subconjunctival and periorbital tissues. The main features are Calabar swellings – painless, localised, transient, hot soft tissue swellings often near joints. They last from a few hours to several weeks. Urticaria, pruritis, lymphoedema, arthritis and chorioretinitis may occur. A meningoencephalitis like picture may occur during treatment.

Onchocerciasis
The incubation period averages 1 year. Initially, a papular, reddish, itchy rash occurs. After repeated infection subcutaneous nodules develop. The nodules may be associated with genital elephantiasis, hydrocele and ocular lesions. Ocular lesions are serious and may cause blindness. Initially, there is excessive tear production, photophobia and the sensation of a foreign body in the eye. Then conjunctivitis, iridocyclitis, chorioretinitis, secondary glaucoma and optic atrophy may occur.

Treatment Wuchereria bancrofti

• Diethylcarbamazine 2 – 6mg/kg daily in divided doses for 2 – 3 weeks. The course is repeated after 6 weeks. Supportive care is antihistamines or steroids for allergic reactions that can occur. Also associated bacterial infections should be treated and reconstructive surgery can be done on unsightly tissue.

Loa loa

• Diethylcarbamazine, 2 - 6mg/kg daily for 2 - 3 weeks

Onchocerciasis

• Ivermectin 150mcg/kg orally as a single dose. Annual retreatment must be given until adult worms die. In endemic areas not all patients need treatment. Indications for treatment are the threat of eye damage and severe pruritis.

Prevention

Primary prevention is aimed at vector control and protection of humans from vectors.

Mass chemotherapy with Diethylcarbamazine is effective in bancroftian filariasis and loasis.

Intestinal

Clinical features

Ascaris lumbricoides (Roundworm)
Infection is acquired by ingesting contaminated food. Infection may be asymptomatic but heavy infections are associated with nausea, vomiting, abdominal discomfort and anorexia. Worms may obstruct the small intestine.

Heavy infections in malnourished children may worsen the malnutrition.

Strongyloides stercoralis
Infection occurs by penetration of the skin by larvae. After penetration of the skin, a local reaction occurs with itching, erythema, oedema and urticaria. This subsides within 2 days. A week later migration of adolescent worms irritates the upper airways, producing cough and occasionally severe respiratory symptoms. After about 3 weeks, intestinal colonization occurs leading to abdominal discomfort, intermittent diarrhoea and constipation.

Heavy infection may lead to persistent diarrhoea, nausea, anorexia and steatorrhoea.

Necator americanus (hookworm)
Local irritation occurs at the site of larval entry in the skin. 2-weeks later mild and transitory pulmonary symptoms appear. Usually, patients are asymptomatic. Once larvae reach the small intestine with heavy infections there may be symptoms and signs of anaemia.

Trichuris trichiura (whipworm)
Most infections are asymptomatic. Heavy infection is associated with bloody diarrhoea and mucus, abdominal discomfort, anorexia and weight loss. It may also cause appendicitis and rectal prolapse in children.

Enterobius vermicularis (threadworm)
Intense anal pruritis which is usually nocturnal. Scratching results in dissemination of eggs.

Diagnosis and Treatment

Ascaris lumbricoides (round worms)
• Mebendazole 100mg twice daily for 3 days.

Strongyloides stercoralis
• Thiabendazole 1.5g twice daily for 2 days OR Albendazole. In the hyper-infected patient with disseminated disease, therapy should be for 5 days or longer. As there may be gram-negative septicaemia in this group treatment should include intravenous broad-spectrum antibiotics.

Hook worm - Necator americanus
• Mebendazole 100mg twice daily for 3 days. A repeated course may be necessary.

Trichuris trichura (whipworm)
• Mebendazole 100mg twice daily for 3 days.

Enterobius vermicularis
• A single dose of Mebendazole 100mg followed by a second dose 2 weeks later. Family members should also be treated.

Prevention Personal hygiene, good sanitation and good living conditions.

Clinical featuresTaenia saginata is prevalent in humans in all beef-eating countries. Taenia solium is found in pork eating areas. Symptoms are mild with vague epigastric and abdominal pain and occasional diarrhoea and vomiting. Weight loss is unusual Appendicitis and pancreatitis rarely occur. Proglottids may be found in the faeces, bed or underclothing.
Diagnosis and TreatmentPraziquantel 10 mg/kg as a single dose.

Prevention Careful inspection of beef or pork for cysticerci (encysted larval forms)
Refrigeration of beef at -10°C for 5 days or cooking at 57°C for a few minutes.

Schistosomiasis (Bilharziasis)

This is caused by blood flukes (trematodes). Human infestations occur after penetration of the skin or mucous membranes by cercaria, the infective form of the host released by the intermediate snail host into freshwater.

The female fluke produces several hundred eggs a day which penetrate the venous walls, creating small bleeding into the urine (Schistosoma haematobium) or stool (Schistosoma mansoni).

Clinical features The first clinical sign is a local inflammatory response - swimmer's itch. Within a week or more there is a more generalised allergic reaction with fever, urticaria and malaise. Nausea, vomiting and profuse diarrhoea as well as respiratory symptoms namely cough are common.

ComplicationsChronic Schistosomiasis with S. mansoni may lead to portal hypertension with marked hepatosplenomegaly. In S. haematobium infestation there is the development of dysuria and haematuria. Later there may be the development of obstructive uropathy, chronic pyelonephritis, renal failure and bladder carcinoma.

Diagnosis and Treatment• Praziquantel tablet Dose:

For Schistosomiasis caused by all species, the usual dosage for adults and children older than 4 years is 60mg/kg body weight given in three equally divided doses in intervals of 4 - 6 hours on the same day. Some clinicians recommend a lower dosage of 40 mg/kg as a single dose or 2 equally divided doses on the same day, which has been effective in the treatment of schistosomiasis in some patients.Prevention: • Use of latrines
• Preventing children from playing in infected water
• Washing with water from a protected well or boiling for 1 - 2 minutes or else use water that has been left to stand for more than 48 hours (this kills the carcaria)