Esa 3 - I & I Session 6B

Front 1

Describe the division of helminths.

Back 1

Helminths are worms which cause investations in humans not infections as they don’t multiply within humans. They can be divided into round worms (nematodes) and flatworms (platyhelminths).
- Roundworms: round body
- Flat worms : flat body: Tapeworms: composed of almost identical segments, Flukes: are not segmented

Front 2

Describe the general life helminth life cycle

Back 2

Ova (eggs) – environmental resistance, often infective by mouth
Larvae – some directly penetrate skin ( SCHISTOSOMA), some are athropod borne ( FILARIASIS - nematodes), and some are responsible for migratory syndromes. In tapeworms encysted forms produce space occupying lesions
Adults – produce eggs, may persist for years and produce chronic disease, may be very BIG.

Front 3

Describe disease associated with ascaris and trichuris.

Back 3

Ascaris lumbricoles and trichuris trichiura are roundworms which cause an intestinal infection. Transmission occurs where there is poor sanitation or when food crops are manured with human faeces. In warm, moist environments the eggs can survive for many years in the soil. The eggs survive in the soil where they mature into infective forms which may be ingested. After hatching in the small intestine into larvae, the organism undergoes a migratory cycle through the liver and lungs where it is coughed up and swallowed, eventually to develop into the adult worm in the intestine. The adult ascaris is found in the intestine and produces 2000 eggs per day which are then excreted.
Ascaris and trichuris infection results in malnutrition as the worms compete for nutrients. The infection is usually asymptomatic but heavy ascaris infection can lead to intestinal obstruction and dysentery. Rectal collapse may also be seen in trichuris infection.
Heavily infected children have poor growth and lowered school performance due to micronutrient deficiency, especially with trichuris infection.
Diagnosis is made by examining up to 2 stool samples for the presence of the characteristic eggs. Treatment is with albendazole.

Front 4

Describe hookworm infection

Back 4

Hookworms are smaller roundworms which don't follow the same pattern as larger roundworms - ascaris lumbricoles. Examples of hookworms include necator americanus and anclyostoma duodenale are gut hemlinths an are prevalent in developing countries. The larvae invade the human directly through intact skin, unlike ascaris where eggs are ingested. Hookworm infections are more serious than ascaris lumbricales as they take blood leading to iron-deficiency anaemia that can be severe. Eggs are found in faeces. Treatment is with albendazole.

Front 5

Describe disease associated with SCHISTOSOMA

Back 5

Schistosomiasis is prevalent in geographic areas where
1. Fresh water is used for bathing or washing
2. Waters are contaminated with human faeces or urine
3. Certain types of snails are present to host the intermediate stages of the parasite
In humans adult worms localise to the mesenteric or pelvic veins. The manifestations of disease are caused by granulomatous reaction to helminth eggs that are trapped in tissues ( eg intestine, bladder, liver).
Schistosoma species are flukes (flatworms) of which 3 species infect humas: schistosoma mansoni, s japonicum, s haemeatobium. It causes chronic infections affecting the hepatic, intestinal and vesical venous systems. The eggs are excreted in the faeces and urine of infected humans. In areas of poor sanitation the eggs hatch releasing a miracidium which invades a snail. After development in the snail, the schistosome cercariae emerges into the environment. The larvae actively penetrate human skin and develop into male and female adult worms that migrate to superior, inferior mesenteric or vesical plexus, where they persist in a permanent state of copulation and the female continuously produces eggs.
Initial infection causes fever, hepatosplenomegaly, skin rash and arthalgia (joint pain). Later bloody diarrhoea or haematuria occurs associated with egg expulsion. Years later fibrosis occurs in the liver ( hepatic fibrosis and portal hypertension), lungs (lung fibrosis) and in the bladder in response to eggs. Space occupying lesion in the brain and spinal cord can cause seizures.
Eggs can be found in stool, urine, rectal snips or tissue biopsy. An EIA detecting antichistosomal antibody is useful. Infection is prevented by appropriate clothing when working in fields and avoiding contaminated water.

Front 6

Describe filariasis

Back 6

Filariasis is caused filarial nematodes ( roundworms) which are transmitted by blood feeding arthropods ( black flies and mosquitos). They cause 3 forms of disease: Lymphatic filariasis results from chronic obstruction of lymphatic system by adult worms and progressive swelling of extremities or genitals (elephantiasis). SUBCUTANEOUS FILARIASIS - Adult worms are often inapparent and lie in the subcutaneous adipose layer but their microfilaria ( larvae) disseminate subcutaneously and produce chronic hypersensitivity reactions which may lead to chronic dermatitis or blindness ( onchocerciasis or river blindness). SEROUS CAVITY FILARIASIS - worms occupy peritoneal cavity.

Front 7

Describe disease associated with ECHINOCOCCUS.

Back 7

Echinococcus granulosus and echinococcus multilocularis cause human hyatid disease. They are tapeworms whose natural hosts are dogs and intermediate hosts are sheep. The eggs are egested in dog faeces and infest sheep where multiple cysts form in liver and lungs. The life cycle is complete when dogs eat infected meat. Humans are accidental hosts and usually live in sheep farming areas are infected by ingesting ova.
Cysts act as space occupying lesions in liver, lungs, abdominal cavity or CNS. Depending on the site of cysts, it causes differnet obstructive problems eg in liver - obstructive jaundice, epigastric pain. hydatid cysts should be surgically removed and albendasole given to kill germinal layer of cyst.

Front 8

Describe the disease associated with TOXOCARA.

Back 8

Toxocara canis are ascaris like roundworms acquired from eggs in dogs faeces and mature in soil. Ingestion is by contamination of food. The larval stages hatch in the intestine, invade the host and migrate to the liver and lungs. They are unable to develop into adults but migrate throughout the body causing fever, hepatosplenomegaly, lymphadenopathy and wheeze. if larva migrate into the eye, sight can be permanently damaged by local inflammatory response of the retina. Larval migratory symptoms may be severe in children. Diagnosis is via specific EIA. Ocular lesions should be treated by steroids.

Front 9

Describe the disease associated with ENTEROBIUS VERMICULARIS

Back 9

Enterobius vermicularis ( pinworm and threadworm) is an ascaris like roundworm which is endemic in Britain and can only infect humans. The female lives in the large intestine and migrates out of the anus at night and lays eggs on peri-anal skin. The eggs can be removed by selotape swab for laboratory diagnosis and D shaped eggs are seen. Symptoms are perianal itching often worse at night and more often seen in children. Scratching allows contamination of the fingers with larvae containing egg which when placed in moth initiate a new cycle of infection. It is often necessary to treat the whole family.

Front 10

Describe disease associated with TAENIA infection.

Back 10

Taenia are tapeworms of which 2 infect humans: Taenia solium, the pork worm and taenia saginata is the beef worm. Tapeworms compete for nutrients and infections are usually asymptomatic.
Taenia solium can use humans as an intermediate as well as the definitive host. The eggs are ingested by eating contaminated pork. They hatch and spread, forming multiple cyst like lesions in the muscles, skin and brain. These lesions are called cysticercosis. Inflammatory responses to parasitic antigens leaking from cysts in the brain may lead to epileptic seizures.
Diagnosis is made by finding eggs in stool sample. Cysticercosis is diagnosed by a specific EIA and confirmed by multiple tissue cysts in x ray, ct or MRI.