Hookworms are a type of roundworm, otherwise known as nematode, that are named for the large hook-like devices that protrude from their oral cavities. Hookworms infect children by penetrating the skin and migrating into the intestine. They then use their hooks to attach to the intestine and break through the gut lining, causing blood to be released. The worms also produce a powerful anticoagulant that prevents the wound from clotting and allows them to keeping feeding. Even through these wounds are tiny, it is estimated that continued feeding by as few as 40 worms can lead to significant anemia in an infected child. The worms can be treated by taking an antibiotic such as albendazole, mebendazole or ivermectin. As of 2010, a vaccine is also undergoing clinical trials.
Necator Americanus
The hookworm species Necator americanus, along with A. duodenale, lives primarily in warm, moist areas with sandy soil. The worms are most abundant in Asia, especially China and sub-Saharan Africa. Walking around barefoot or having other bodily contact with the ground allows the infective larvae to penetrate the skin. They then migrate into the lungs over the next 10 days, sometimes leading to a cough and sore throat. When the microscopic larvae are coughed up from the lungs, they are able to enter the gut and travel down into the intestine. The larvae then attach to the intestine wall and, using the child's blood for nutrition, develop into adults and produce eggs. These eggs are released back into the environment via the stool.
The chronic blood loss caused by even a modest worm burden leads to significant morbidity for millions of children worldwide. Anemia, or decreased numbers of red blood cells, leads to a decreased ability to deliver oxygen to the tissues of the body. The consequences of chronic hookworm-related anemia include iron deficiency, protein loss, poor nutrition, short stature and cognitive deficits.
Ancylostoma Duodenale
The hookworm Ancylostoma duodenale very similar to N. americanus in its life cycle and its ability to lead to debilitating anemia through chronic blood loss. A. duodenale is does have a few distinguishing characteristics, however. For one, it is limited to a smaller geographic region, including the Mediterranean, parts of South America, and northern Asia. Additionally, A. duodenale can cause infection when it is ingested as well as by penetrating the skin. This means that a child in an endemic area can also be at risk from eating food that is not thoroughly washed or if he accidentally ingests dirt.
Ancylostoma Brazilense
Ancylostoma brazilense is another skin-penetrating hookworm species that primarily infects dogs. Sometimes the larvae accidentally infect humans. When A. brazilense gets into the skin of humans, it burrows in the skin and causes a long, crooked, linear red rash. These larvae are typically unable to penetrate further into humans, however, so they will die in the skin and the infection will resolve without treatment. Albendazole can be used to hasten death. This infection is also referred to as cutaneous larva migrans.
Ancylostoma Caninum
Ancylostoma caninum is a zoonotic hookworm species that primarily infects dogs. Occasionally, humans can become infected by A. caninum as well. The same treatment is used as with the more typical human hookworm infections.
References
- "New England Journal of Medicine"; Hookworm Infection; Dr. Peter J. Hotez et. al.; August 2004
- "Red Book: 2009 Report of the Committee on Infectious Diseases, 28th ed."; Hookworm Infections (Ancylostoma duodenale and Necator americanus); L.K. Pickering, ed.; 2009
- "Pediatrics"; Hookworms (Necator americanus and Ancylostoma spp.); Dr. Peter J. Hotez; August 2007
