Worm infection is still common in developing countries (tropical countries) due to pausity of potable water, poor personal hygiene, and poor sanitary facilities. Disposal of feacal waste even in some cities is insanitary, sometimes dumped in rivers or streams.
A large proportion of the population in developing countries do open defeacation, thus contaminating the soil. In the rural areas , there are no toilets, few boreholes are productive, few sanitary wells exist and the knowledge of water hygiene is non-existent or very rudimentary.
Worm infection in many cases spreads through the mouth from contaminated hands or drinking contaminated water or through skin penetration.
However, worm infection is not restricted to the tropics, certain infections occur worldwide. Some of the infections are without symptoms, while others are responsible for blindness, anaemia, various disabilities etc.
The following are some of the worm infections still common in developing countries:

Hookworm infection is caused by two parasites (Ancylostoma duodenale and Necator Americana) and occurs worldwide, affecting about 1.5 billion globally. Of this figure over 1 billion occur in developing countries.
All ages are affected but children are more susceptible for obvious reasons as they are always on playgrounds and are yet to imbibe the tenets of personal hygiene.
Mode of transmission is mainly by penetration of skin by the worm larva present in the soil due to contamination by human feaces. Other modes include ingestion of food contaminated by the worm larva (only Ancylostoma duodenale), eating uncooked meat that has the larva and also through human milk.
Promoting factors include in-proper disposal of feaces, poor sanitation facilities, poverty, use of feaces as fertilizer etc.
Symptoms include itching at site of entry of the parasite, bloody stools, and anaemia.

2.Roundworm (ascariasis)
Roundworm infection is the most common worm infection worldwide, affecting over 1.5 billion globally. However it is most common in developing countries like Nigeria, India, China, Brazil and Indonesia. It is caused by a parasite called Ascaris lumbricoides.  This is a large round worm which inhabits the small intestine where it produces eggs that are passed out with feaces.
Mode of transmission is orally by hands contaminated by soil containing eggs of the parasite. That is why the infection is most common in children.
Promoting factors include raining season, in-proper disposal of feaces, poor sanitation facilities, level of education, use of feaces as fertilizer etc.
Symptoms include fever, cough, intestinal obstruction which could lead to vomiting and abdominal pain

Whipworm infection occurs worldwide and inhabits the large intestine; it is caused by a parasite called Trichuris trichuria. It affects about 1 billion people globally with majority of  them in developing countries. All age groups are affected but children are most susceptible.
It also affects pigs.
Transmission is by ingestion through contaminated fingers; the adults produce eggs in the human large intestine which are passed out with feaces to contaminate the soil.
Promoting factors include heavy rainfall, in-proper disposal of feaces, poor sanitation facilities, level of education, use of feaces as fertilizer and poor personal hygiene.

Threadworm infection also called Pinworm infection is caused by Enterobius vermicularis; it occurs worldwide but mostly in developing countries. All ages are affected but children are most susceptible.
Transmission occurs by any of the following methods : from the anal area to the mouth with our fingers; by ingesting eggs present in soiled bed sheets and other contaminated objects; via nose or mouth from contaminated dust; or from the anus right back into the rectum. Consequently a whole family can easily be affected.
Symptoms include intense itching around the anus at night due the adult female worm coming to the anal area to lay her eggs, bedwetting and itching /inflammation of the vagina.
Promoting factors include poor personal hygiene and low socio-economic status.

Tapeworm occurs worldwide but most common in Mexico, countries in Central and South America, the Philippines and some other countries in South-east Asia. About 20 million persons are affected annually all over the world with about 50,000 deaths.
It is caused by two parasites: Taenia solium and Taenia saginata
Symptoms are uncommon but could be severe if they occur. They include convulsions, loss of sensation, paralysis, severe headache, blindness and several others.
Transmission is by eating uncooked or partially cooked pork or beef. Man passes the eggs out with stool and sheep/pigs get infected by eating contaminated grass or feaces respectively. The eggs then develop in the sheep or pig to the intermediate stage, man gets infected if the affected animal is eaten without being properly cooked.
Promoting factors include in-proper disposal of feaces, poor sanitation facilities, poor food hygiene and use of feaces as fertilizer.

Guineaworm infection used to be worldwide but now restricted to a few countries in West and Northeast Africa. It is caused by a parasite called Dracunculus medinensis.
Transmission is by ingestion of water containing water fleas (Cyclops) that has the parasites.
Symptoms include fever, feeling of being unwell, swelling on the lower leg which could become a sore with the worm visible.
Promoting factors include absence of potable water and poor water hygiene.

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