ANCYLOSTOMA NECATOR

An estimated 576-740 million people in the world are infected with  hookworm. Hookworm was once widespread in the United States, particularly in the southeastern region, but improvements in living conditions have greatly reduced hookworm infections. Hookworm, Ascaris, and whipworm are known as soil-transmitted helminths (parasitic worms). Together, they account for a major burden of  disease worldwide.

Hookworms live  in the small intestine. Hookworm eggs are  passed in the feces of an infected person. If the infected person defecates outside (near bushes, in a garden, or  field) of if the feces of an infected person are used as fertilizer, eggs are  deposited on soil. They can then mature  and hatch, releasing larvae (immature worms). The larvae mature into a form that can penetrate the skin of humans. Hookworm infection is mainly acquired by walking barefoot on contaminated soil. One kind of hookworm can also be transmitted  through the ingestion of larvae.

Most people infected  with hookworms have no symptoms. Some  have gastrointestinal symptoms, especially persons who are infected for the  first time. The most serious effects of  hookworm infection are blood loss leading to anemia, in addition to protein loss. Hookworm infections are treatable with  medication prescribed by your health care provider.

FAQS

What is hookworm?

Hookworm is an intestinal parasite of humans.  The larvae and adult worms live in the small intestine can cause intestinal disease. The two main species of hookworm infecting  humans are Anclostoma duodenale and Necator americanus.

How is hookworm spread?

Hookworm eggs are passed in the feces of an infected  person. If an infected person defecates  outside (near bushes, in a garden, or field) or if the feces from an infected  person are used as fertilizer, eggs are deposited on soil. They can then mature and hatch, releasing  larvae (immature worms). The larvae  mature into a form that can penetrate the skin of humans. Hookworm infection is transmitted primarily  by walking barefoot on contaminated soil. One kind of hookworm (Anclostoma  duodenale)can also be  transmitted through the ingestion of larvae.

Who is at risk for infection?

People living in areas with warm and moist climates and where  sanitation and hygiene are poor are at risk for hookworm infection if they walk  barefoot or in other ways allow their skin to have direct contact with contaminated  soil. Soil is contaminated by an infected  person defecating outside or when human feces ("night soil") are used as  fertilizer. Children who play in  contaminated soil may also be at risk.

What are the signs and symptoms of hookworm?

Itching and a localized rash are often the first signs of infection. These symptoms occur when the larvae  penetrate the skin. A person with a  light infection may have no symptoms. A  person with a heavy infection may experience abdominal pain, diarrhea, loss of  appetite, weight loss, fatigue and anemia.  The physical and cognitive growth of children  can be affected.

How is hookworm diagnosed?

Health care providers can diagnose hookworm by taking a stool sample  and using a microscope to look for the presence of hookworm eggs.

How can I prevent infection?

Do not walk barefoot in areas where hookworm is common and where there  may be fecal contamination of the soil. Avoid  other skin-to-soil contact and avoid ingesting such soil. Fecal contamination occurs when people  defecate outdoors or use human feces as fertilizer.  

The infection of others can be prevented by not defecating outdoors or  using human feces as fertilizer, and by effective sewage disposal systems.

What is the treatment for hookworm?

Hookworm infections are generally treated for 1-3 days with medication  prescribed by your health care provider. The drugs are effective and appear to have few side effects. Iron supplements may be prescribed if you  have anemia.

What is preventive treatment?

In developing countries, groups at higher risk for soil-transmitted helminth infections (hookworm, Ascaris, and whipworm) are often treated without a prior stool examination. Treating in this way is called preventive treatment (or "preventive chemotherapy"). The high-risk groups identified by the World Health Organization are preschool and school-age children, women of childbearing age (including pregnant women in the 2nd and 3rd trimesters and lactating women) and adults in occupations where there is a high risk of heavy infections. School-age children are often treated through school-health programs and preschool children and pregnant women at visits to health clinics.

What is mass drug administration (MDA)?

The soil-transmitted helminths (hookworm, Ascaris, and whipworm) and four other "neglected tropical diseases" (river blindness, lymphatic filariasis, schistosomiasis and trachoma) are sometimes treated through mass drug administrations. Since the drugs used are safe and inexpensive or donated, entire risk groups are offered preventive treatment. Mass drug administrations are conducted periodically (often annually), commonly with drug distributors who go door-to-door. Multiple neglected tropical diseases are often treated simultaneously using MDAs.

EPIDEMIOLOGY & RISK FACTORS

Hookworm is a soil-transmitted helminth (STH) and is one of the  most common roundworm of humans. Infection is caused by the nematode parasites Necator americanus and Ancylostoma duodenale. Hookworm infections often occur in areas where human feces are used as fertilizer or where defecation onto soil happens.

GEOGRAPHIC DISTRIBUTION

The geographic distributions of the hookworm species that are  intestinal parasites in human, Ancylostoma  duodenale and Necator americanus, are worldwide in areas with warm, moist climates and are widely  overlapping. Necator americanus was widespread in the Southeastern United States  until the early 20th century.

BIOLOGY

Causal Agent:

The human hookworms include the nematode species, Ancylostoma duodenale and Necator americanus.

Life Cycle:

Eggs are passed in the stool, and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil, and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective. These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed. The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host. Most adult worms are eliminated in 1 to 2 years, but the longevity may reach several years.

Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle). In addition, infection by A. duodenale may probably also occur by the oral and transmammary route. N. americanus, however, requires a transpulmonary migration phase.

Life cycle image and information courtesy.

DISEASE

High-intensity hookworm infections occur among both school-age children and adults, soil-transmitted helminthsAscaris and whipworm. High-intensity infections with these worms are  less common among adults. The most  serious effects of hookworm infection are the development of anemia and protein  deficiency caused by blood loss at the site of the intestinal attachment of the  adult worms. When children are  continuously infected by many worms, the loss of iron and protein can retard  growth and mental development.

DIAGNOSIS

The standard method for diagnosing the presence of hookworm is by identifying  hookworm eggs in a stool sample using a microscope. Because eggs may be difficult to find in  light infections, a concentration procedure is recommended.

PREVENTION AND CONTROL

The best way to avoid hookworm infection is not to walk barefoot in areas  where hookworm is common and where there may be human fecal contamination of  the soil. Also, avoid other skin contact  with such soil and avoid ingesting it.

Infection can also be prevented by not defecating outdoors and by effective sewage disposal systems.

For more information view the source:Center for Disease Control

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