Helminths in tropical regions

Schistosoma spp. Blood flukes Schistosomiasis is one of the most widespread parasitic infections in humans Humans are the principal hosts for: Schistosoma mansoni, Schistosoma japonicum, Schistosoma mekongi, Schistosoma haematobium, and Schistosoma intercalatum Human schistosomiasis occurs in about 200 million people worldwide The disease is present in freshwater areas of Africa, Asia, and South America

Epidemiology

Epidemiology S. mansoni is present in Africa, South America, many islands in the Caribbean, and the Middle East, especially in the Nile Valley S. japonicum is present in China S. mekongi is present in Laos and Kampuchea in Southeast Asia. S. haematobium occurs in the Middle East and in parts of Africa S. intercalatum occurs in Africa

Schistosoma spp. Stages in the Life Cycle

1. Worms are about 1 to 2 cm in length and are of separate sex. It is estimated that the worm can survive for as long as 30 years. 2. S. mansoni, S. japonicum, and S. mekongi worms live in the terminal venules of the portal and mesenteric blood vessels. 3. S. haematobium lives within the vesical plexus around the bladder. 4. Half of the eggs pass through the bladder wall or the intestinal wall, out into the environment. 5. The remainder of the eggs stay locally or pass along the blood vessels. 6. Once eggs are passed into fresh water, they develop into motile miracidia that live within snails. 7. After 4 to 6 weeks, the miracidia evolve into cercariae, by which they can pass into the water and infect humans. 8. Infection in humans occurs through the skin, where the cercariae then migrate to the liver. 9. After 6 weeks of development, the adult worm descends into the portal veins or the vesical plexus. Life Cycle

Epidemiology

Cercaria Infective Stage

Schistosoma spp. Intermediate host

Symptoms A papular skin rash, lasting 24 to 48 hours, occurs in the location of the skin penetration by the cercariae. 4 to 8 weeks after infection, patients develop fevers with chills, headaches, and cough. This occurs during oviposition and is known as Katayama fever. It occurs due to the antigenic stimulation produced by the laying of the eggs. Symptoms regress after 2 to 4 weeks. During the chronic phase, which may last many years, patients may note abdominal pain and diarrhea. Over years, eggs that pass through the liver lead to granulomata formation and portal hypertension, and liver enlargement. Over many years, patients develop decompensated liver disease, ascites, and death due to liver failure or due to variceal bleeding. Eggs that bypass the liver in patients with portal hypertension can lodge in the lungs and produce pulmonary hypertension. Patients with S. haematobium pass eggs into the genitourinary system. Reaction to the eggs can lead to urinary obstruction, bladder dysfunction, and hematuria. Renal failure may occur as a late event. Eggs of S. japonicum can pass into vessels of the brain, causing seizures of vessels, or into the spinal cord, causing transverse myelitis.

Chronic schistosomiasis portal hypertension and ascites

China, 1960

Lab Dg Eggs can be isolated from the feces or urine of infected patients. Serologic tests are available to diagnose light infections. Liver function tests are frequently normal. Eosinophilia is observed in most cases. Anemia due to chronic blood loss is mild.

Treatment Praziquantel Metrifonate Oxamniquine

Prevention Improve sanitation so that eggs do not pass into areas where snails reside. Reduce snail populations with molluscicides. Prohibit swimming in contaminated waters.

FILARIAE

Filariae Filariasis connotes a wide range of tissue-dwelling nematodes within the superfamily Filaroidea. Organisms live within skin and connective tissue, lymphatics, and blood vessels. The adult worm may live in the host for over 20 years.

Filariae Frequent species Zoonotic species Wuchereria bancrofti Loa loa Onchocerca volvulus Brugia malayi Brugia timori Mansonella perstans Mansonella ozzardi Mansonella streptocerca Dirofilaria spp. Other Dracunculus medinensis

Filariae Wuchereria bancrofti The adult worm lives within the lymphatic system Enters the human host after the mosquito bite Present worldwide throughout the tropics and transmitted from mosquitos It is estimated that 250 million people are infected with worms that produce lymphatic filaria Disease that causes lymphatic destruction and elephantiasis is caused also by Brugia malayi, and Brugia timori Loa loa Enters the human host after a tabanid fly bite Worm migration leads to localized swelling, called Calabar swelling L. loa is present in West and Central Africa Onchocerca volvulus Enters the human host after a black fly bite Disease seen in South America and Africa Patients have inflammation of the skin and eye, which can lead to blindness. In Africa, the disease is termed river blindness

Life Cycle

Wuchereria bancrofti

Wuchereria bancrofti - Symptoms Patients often have recurrent episodes of lymphangitis and lymphadenitis. The femoral/inguinal nodes are often affected, and the epididymis and spermatic cord become enlarged. Over time, hydroceles develop that may be massive. Disease in the lower extremity can lead to elephantiasis. Other syndromes associated with lymphatic filariasis include monoarticular arthritis and tropical pulmonary eosinophilia.

Pathology

Pathology HYDROCOELE

Lab dg Adult worms are infrequently recovered. Analysis of blood may reveal the microfilaria. Blood samples are often taken at midnight, when the concentrations of filaria are the highest!!!!!! Serologic diagnosis is available, yet cross-reacting antibodies are common. Eosinophilia is often absent.

Lab dg

Brugia malayi

Loa loa Life Cycle

Symptoms Adult worms may pass under the conjunctiva or through the skin. The worm often takes minutes to transverse vessels in the conjunctiva and then disappears. This organism is associated with very little pruritus. Calabar swelling is often seen in the wrists and ankles; swelling may last only hours but can be recurrent for years.

Loa loa Parasite under the skin Calabar swelling

Lab dg Diagnosis is clinical. Microfilaria can be isolated from the blood. Adult worms can be identified if they are isolated. Blood samples taken at noon have the best yield!!!!! Serologic diagnosis is not reliable.

Onchocerca volvulus Life Cycle

Symptoms Skin changes vary from papular rashes to extensive areas of hyperor hypopigmentation. Patients may have eczematoid dermatitis and thickening of the skin. Much pruritus is noted. Nodules in the subcutaneous regions reflect areas of inflammation in sites where worms live. They are nontender and may be many centimeters in diameter. Onchocerciasis can lead to blindness due to keratitis, optic atrophy, and choroidoretinitis.

Subcutaneous nodule

Dermatitis Hanging groin

Pathology

Lab Dg Parasitologic diagnosis is made by obtaining a minute, bloodless skin snip and observing the larvae migrating out of the skin under a microscope. Serology is also available but of little use in patients in endemic regions. Eosinophilia is present.

Dracunculus medinensis Essentials Dracontiasis, Guinea worm infection Dracunculiasis or guinea or Medina worm infection is caused by the tissue nematode Dracunculus medinensis. The worm has an indirect life cycle with small copepods as intermediate hosts. Epidemiology Guinea worm infection is endemic in the Middle East, and in central and western Africa, mainly in rural areas Control has been achieved through international efforts in many countries except in areas with social unrest. Eradication remains a distant goal! Infection occurs by ingestion of infected copepods with the drinking water Diagnostic strategies Clinical findings are characteristic and no special diagnostic strategy is needed.

Humans become infected by drinking water containing copepods which contain larve of D. medinensis. Following the ingestion, the copepods die and release the larve, which penetrate the host intestine and enter abdominal cavity. After maturation and copulation, the male worms die and the females (70-120 cm) migrate in the subcutaneous tissues towards the skin surface. Approximately one year after infection, the female induces a blister on the skin, generally on the distal lower extremity, which ruptures. When this lesion comes into contact with water, the female worm emerges and releases larvae. Larvae are ingested by a copepod and after two weeks develop into infective larve. Ingestion of the copepods closes the cycle.

Epidemiology

Pathology

Prevention and Control The easiest personal control measure is to filtrate water before use Health education To improve the water supply of affected communities