Helminth diseases are caused by parasitic worms known as helminths. These worms are categorized into three main categories: roundworms, tapeworms, and flukes. There are around 300 identified helminths that infect humans. Transmission of helminths typically involves direct contact with the parasite, or ingestion of the parasite via contaminated food or water. In some cases, the parasites can pass through human skin from infected water or soil.
Symptoms range depending on the type of helminth causing the disease. There may be general symptoms, or more specific symptoms as certain regions of the body are affected. Furthermore, while full recovery is possible from some infections, death or debilitating disabilities occurs with other infections. Treatment, when possible, usually involves administration of anti-inflammatory drugs alone or in combination with anti-helminth drugs that kill the existing parasites in various stages of their development.
Helminths cause human disease worldwide, although climate conditions limit many species of helminths to tropical or semi-tropical areas. However, with changes in climate, certain infections are becoming widespread. Developing or poverty-stricken countries are heavily affected with helminth diseases, a problem compounded by lack of education, funding, and additional problems in these countries such as HIV infection, lagging infrastructure, political instability, and war.
Helminths are parasitic worms, that is, they infect a host and survive by feeding off the host's nutrients, a process that usually harms the host. The adverse effects of the helminth lead to the development of disease within the host. There are roughly 300 recognized helminths that infect humans. Helminths are thought to have been present in humans as far back as ancient Egyptian times, and gradually, specific disease-causing species were identified over the centuries. The study of helminths increased in the twentieth century, which caused the number of recognized helminths to increase from 28 to over 300.
Helminths are separated into three main categories based on morphology (structure) and mode of transmission. These categories are roundworms or nematodes, tapeworms or cestodes, and flukes or trematodes.
Most roundworms hatch and live in the intestines. The eggs of roundworms enter the body of the host and travel towards the intestines, where they hatch. Depending on their subtype, they remain in the intestine or migrate to other regions of the body. Transmission of roundworms occurs when contaminated material enters the body. This could be via ingestion of contaminated food or water, entry of eggs via the anal or genital tracts, or ingestion of, or contact with, contaminated soil. Symptoms of roundworm infection vary depending on the type of worm. Some cause general symptoms such as abdominal pain, diarrhea, fatigue, itching, and fever, while others can be more specific and cause damage to certain regions of the body.
Tapeworms generally live in the intestines. Their eggs are normally ingested when meat containing the parasites is undercooked or raw. While symptoms may not occur, some patients will experience abdominal pain, fatigue, and diarrhea.
Flukes are a group of helminths that live in various regions of the body including the spleen, liver, lungs, and intestines. The lifecycle of these worms involves freshwater snails as intermediate hosts. Following the release of larval forms of the worm from the snail into fresh water, the larval worms can enter humans via contact with the skin. Most cases of fluke infection do not cause initial symptoms, and the parasites pass out of the body. However, reinfection can occur. If it occurs continuously over time, this can cause damage to body organs. In symptomatic cases, infection usually results in a rash, itching, muscle aches, coughing, chills, and fever. Severe infections involve flukes entering the liver, lung, or brain and spinal cord.
Helminth diseases occur worldwide. However, different types of infections are present in different regions. One factor that influences where an infection can occur is climate. Some helminths survive only in tropical climates, while others require temperate conditions.
Soil-transmitted helminths and schistosomes, a type of trematode, are the cause of most of the world's helminth disease burden. Regions that are poverty-stricken, in the midst of conflict, or have low sanitation standards have a high prevalence of infection. Poverty-stricken countries in the developing world, located in Africa, China, East Asia, and the Americas, account for most of the world's helminth infections.
However, some infections of helminths are common in developed countries. For example, infection by the pinworm, a nematode that causes itching, is common in temperate areas such as Western Europe and North America. Large infection rates are recorded for these regions. Cambridge University reports infection in 30% to 80% of Caucasian children in the United States, Canada, and Europe. Despite its large prevalence in the temperate zone, this infection is rare in the tropics.
As there are a large variety of helminths that cause disease in humans, there is no specific treatment. However, most infections can be treated via the use of vermifuges, which are anti-worm drugs that effectively kill parasitic worms. In addition, while some helminth infections can be cured within a short period of time, others may take months or years to heal, and in some cases, patients are left with debilitating disabilities due to organ and limb damage.
There are several ways to prevent infection from helminths. First, avoiding contact with the parasites ensures infection does not occur. Contact can be prevented by frequent washing of hands, maintaining a clean bathroom and kitchen, and avoiding contact with infected animals. Furthermore, thorough cooking of food, particularly pork and beef that may potentially carry parasites, prevents ingestion of parasites. Chlorinating, filtering, or boiling drinking water prevents parasites being ingested while drinking. To avoid parasite uptake while bathing or swimming in infected water, a problem particularly for fluke parasites, water can be boiled prior to bathing, or avoided completely.
Another way to prevent infection is to lower the prevalence of helminths within a community. This is achieved through regular deworming, or administration of anti-worm treatments to infected people. This can effectively reduce the long-term effects of the parasites on infected persons, as well as reduce the prevalence of the parasite within a community.
In order to effectively implement prevention methods in communities affected by helminth infestations, communities can be educated about hygiene, sanitation, and proper food preparation. Together with helminth treatments, these methods help to reduce the prevalence and effects of helminths on communities.
WORDS TO KNOW
HELMINTH: A representative of various phyla of worm-like animals.
HYGIENE: Hygiene refers to the health practices that minimize the spread of infectious microorganisms between people or between other living things and people. Inanimate objects and surfaces such as contaminated cutlery or a cutting board may be a secondary part of this process.
MORPHOLOGY: The study of form and structure of animals and plants. The outward physical form possessed by an organism.
SANITATION: Sanitation is the use of hygienic recycling and disposal measures that prevent disease and promote health through sewage disposal, solid waste disposal, waste material recycling, and food processing and preparation.
Parasitic infections are a worldwide issue as millions of people become infected by helminths every year. Although knowledge about helminths is increasing, the prevalence of infections is also increasing rather than declining. There are a number of reasons for this occurrence.
The Human Immunodeficiency Virus (HIV) and AIDS causes decreased immunity in infected people, and makes them more susceptible to infection by emerging parasites that are taking advantage of weakened immune systems. Furthermore, existing helminth infections also take advantage of people with low immunity and have increased as a result. This problem compounds when countries with a high prevalence of HIV infection also have a high prevalence of helminth infection.
Helminth invasion into new areas has also become a major contributor to global increases in infection. This is initiated by changes in the climate that make previously helminth-free regions suitable for helminths to survive and reproduce. In addition, war and its resulting social upheaval results in lower standards of sanitation and nutrition that has lead to re-emergence of helminth infections in some populations. Helminth resistance to anti-worm drugs has also caused issues in controlling and treating infections.
The World Health Organization (WHO) estimates that nearly one billion people worldwide do not have access to clean drinking water. Water polluted by sewage, refuse, and agricultural byproducts (such as manure) spreads some helminths. Several international organizations help communities build wells, water purification stations, and sewage collection systems.
Several world leaders serve as advocates for international, cooperative anti-helminth efforts, including former United States President Jimmy Carter (1924–), Amadou Toumani Touré (1948–) of Mali, and Yakubu Gowon (1934–) former Nigerian head of state. The Carter Center's International Task Force for Disease Eradication, with support from the Bill & Melinda Gates Foundation, sponsors anti-helminth programs with the aim of eradicating dracunculiasis (Guinea worm disease) and lymphatic filariasis across the globe, eradicating onchocerciasis (river blindness) in the Americas, and controlling schistosomiasis.
IN CONTEXT: DISEASE IN DEVELOPING NATIONS
Helminth diseases are most likely to strike children, especially in the developing world, causing malnutrition and illness. Malnutrition during childhood has life-long effects on an estimated 182 million children worldwide, from increased rates of illness and stagnated development, to disability and premature death. Thus, the World Health Organization (WHO), in partnership with UNICEF, focuses its anti-helminth efforts on children and schools. In areas where helminths thrive in local water or soil, efforts to curb helminth diseases include food safety, hygiene, and sanitation education, as well at the widespread administration of anti-helminth drugs. Such comprehensive public health measures have reduced incidence of helminth diseases in limited parts of Indonesia by as much as 50%.
See AlsoAIDS (Acquired Immunodeficiency Syndrome); Bilharzia (Schistosomiasis); Climate Change and Infectious Disease; Dracunculiasis; Emerging Infectious Diseases; Handwashing; HIV; Hookworm (Ancylostoma) Infection; Liver Fluke Infections; Lung Fluke (Paragonimus) Infection; Opportunistic Infection; Pinworm (Enterobius vermicularis) Infection; River Blindness (Onchocerciasis); Roundworm (Ascariasis) infection; Sanitation; Tapeworm Infections; War and Infectious Disease; Water-borne Disease.
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Cox, F.E.G. “History of Human Parasitology.” Clinical Microbiology Reviews. vol. 15, no. 4 (2002): 595–612.
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