- Ascariasis (round worm)
This is the largest intestinal worm that affects human beings. It is as large as 40 cm in length and lives in the small intestine. The female worm can produce hundreds of thousands of eggs (ova) in a day. The eggs are passed in the faeces and released into the soil where they may remain for months or years.
Causative Agents: Ascaris Lumbricoids
Modes of transmission
Round worm usually results from drinking contaminated water or by eating of contaminated vegetables or food. Infection can also result from eating with hand that is contaminated with faecal matter.
In humans, the eggs hatch in the bowel and migrate through the intestine to the liver, heart and lungs. From the lungs they are carried up the trachea or wind pipe and are later re-swallowed back into the intestine, where the eggs develop and mature.
The mature worm mate and the females lay eggs which are again passed in the faeces thus repeating the life cycle. Children of school age are mostly the victims of the infection.
Symptoms: Abdominal pain, vomiting, loss of weight, etc.
Prevention: Prevention involves good personal hygiene, washing hands after going to toilet and before meal and the use of latrine or flush toilets. The infected person should be treated with worm expellers.
- Tapeworm infection(taeniasis)
Tapeworm is a big segmented flat worm with a rounded head containing suckers with which it attaches to the intestinal wall. Teaniasis or tapeworm infection occurs in all countries where beef or pork is eaten. The world incidence of tape worm is much higher than that of pork tapeworm. Beef tapeworm is uncommon in young children and the incidence with age.
The main sources of tapeworm are improperly cooked meat (beef or pork) and fish. The beef or cattle tapeworm is Teania Saginata while the pork or pig tapeworm is Teania Solilum
Incubation Period: 8 – 10 weeks
Tapeworms have both male and female organs. They live in the human intestines producing eggs which are passed in faeces. Their secondary life is in cow or pig that pig the eggs from contaminated faeces. Humans are again infected when eating the infected meat or by ingestion of food or water.
Symptoms: Recurrent abdominal pains, fatigue and loss of weight.
Prevention: Prevention is by proper cooking of meats cut into smaller sizes.
- Hookworm disease (ancyclostomiasis)
Hookworm infestation is the most deadly of all the intestinal worms, causing anaemia and disability. The worms live in the small intestine where they suck blood. Hookworm is endemic in tropical and subtropical countries where sewage disposal is inadequate. There are two main species of the worm. Nector Americans and Ancylostoma duodenale which are found in different parts of the world.
Hookworms are about 1cm long. The female worms lay eggs which are passed in faeces deposited on the ground or soil. They hatch and the larvae become infective. Infection occurs when the larvae penetrates the skin especially barefoot. From the skin they pass into the bloodstream to the lungs and then trachea where they are coughed up and then swallowed into the stomach and small intestine. Here they hook to the walls of the small intestine and suck blood. The female produce thousands of eggs which are then excreted in faeces and the cycle continues.
Incubation Period: Few days to months or even years
Symptom: Sucking of blood results in hookworm anaemia. The loss of blood result into tiredness, aching muscles, swelling of legs, abdominal pains, diarrhoea with mucus or blood.
Prevention: Proper sewage disposal, personal hygiene and wearing of shoes.
Dracunculiasis (guinea worm)
Dracunculiasis or guinea worm disease is a vector-borne parasitic disease, mainly of the subcutaneous tissues (usually leg and foot) caused by the nematode parasite, Dracunculus medinensis. This parasitic disease can disable its victims temporarily.
Natural history of dracunculiasis (guinea worm)
Agent: The adult parasite inhabits the subcutaneous tissue mainly of the legs but of other parts of the body, including the head and neck. The gravid female makes her way down to the infected person’s lower limbs near the skin surface. She penetrates into the dermis and induces an inflammatory reaction and subsequent blister formation. Upon contact with water, the blister soon ruptures and the parasite release up to one million, microscopic, free-swimming larvae into water. The larvae may remain active in water for 3 – 6 days. They are picked up by small fresh-water crustaceans called cyclops. The larvae require a period of about 15 days for development in cyclops, which is the intermediate host.
Man acquires infection by drinking water containing infected cyclops. In the human body, digested by gastric juice, the parasites are released. They penetrate the duodenal wall. Subsequently, they migrate through the viscera to the subcutaneous tissues of various parts of the body.
Reservoir of infection: An infected person harbouring the gravid female. The possibility of an animal reservoir exists but not proved.
Host factors: Host susceptibility is universal. Multiple and repeated infections may occur in the same individual. The habit of washing and batting in surface water and using step-wells is important.
Environmental factors: The main link of transmission of guinea worm disease is water infected with cyclop. The risk of transmission exists where such cyclops infested water sources are frequented by infected person.
Mode of transmission: the disease is transmitted entirely through the consumption of water containing cyclops harbouring the infective stages of the parasite. Guinea worm disease is a totally water-based disease and does not have an alternative pathway of transmission.
Preventing/control measures of dracunculiasis (guinea worm)
- Provide portable water. Abolish step-wells and take other measures, such as the use of occlusive bandages to prevent contamination of drinking water by infected persons immersing feet or other parts of the affected body in water.
- Boil drinking water, filter through fine mesh cloths to remove cyclops.
- Educate the public to drink only boiled and filtered water from the close or pump-well. Instruct infected person on mode of spread of infection and the danger in contaminating wells or other water supplies.
Schistosomiasis (bilharziasis)
Schistosomiasis (also known as bilharziasis snail fever and Katayama fever) is caused by parasitic worms of the Schistosoma type. It may infect the urinary tract or intestines.
Mode of transmission of schistosomiasis (bilharziasis)
The disease is spread by contact with water that contains the parasite. These parasites are release from fresh-water snails that have been infected. The disease is especially common among children in developing countries as they more like to play in infected water. Other high groups include farmers, fishermen and people using infected water for their daily chores.
Symptoms of schistosomiasis (bilharziasis)
Symptoms may include abdominal pain, diarrhoea, blood stool, or blood in urine. In those who have been infected a long time, liver damage, kidney failure, infertility or bladder cancer may occur. In children it may cause poor growth and learning difficulty.
Methods of prevention of schistosomiasis (bilharziasis)
Methods of prevention of the disease include improving access to clean water and reducing the number of snails. In areas where the disease is common entire groups may be treated all at once and yearly with the medication-praziquantel. This is done to decrease the number of people infected and therefore decrease the spread of the disease.