After travelling through the countryside of Vellore, the most prevalent tropical disease that I came across was anemia secondary to parasitic infection. Therefore I thought that it would be fitting to write my tropical disease paper on hookworms.
The hookworm is a parasitic nematode that lives and thrives in the small intestine of its host, and is thought to infect about 800 million people in tropical nations. The prevalence of infection in moist tropical climates can be as high as 80%, compared to 10% in drier climates. There are two common species that infect humans: Ancylostoma duodenale and Necator americanus. The species A. duodenale predominates throughout India.
The most significant risk of hookworm infections is anemia, secondary to loss of iron, and protein, in the gut. A duodenale and N americanus are about a centimeter long and off-white in color. The larvae emerge from passed eggs within 24 hours and molt once to an infective filariform larval stage in another 24 hours. After molting, larvae are able to penetrate intact skin. Walking barefoot in soil contaminated with feces is the most common method of exposure. After skin penetration, the larvae travel through the venous circulation until they reach the pulmonary capillaries. Within 3-5 days, the larvae travel through alveoli and travel up the ciliary escalator from the lungs into the pharynx. Once in the pharynx, larvae are swallowed and travel to the GI tract, where they attach to the wall of the intestine and begin to feed on the blood of the host. The hookworm consumes approximately 0.3-0.5 mL of blood each day. This chronic blood loss often goes unnoticed in the villages until severe anemia is present. Understanding the life cycle of the worm sheds light onto why so many villagers are infected. Hygiene is extremely poor and there is usually only a plot of land on which to defecate. Furthermore, most of the villagers are too poor to own shoes.
There are very few symptoms of hookworm infection, until anemia is present. Early symptoms include a “ground itch” at the site of larvae penetration. The migrating worm may cause a low-grade fever or cough. The late symptoms may include GI discomfort. The blood expelled by the worm occult and therefore difficult to notice. Once anemia develops, the patient will most often present with fatigue and dyspnea.
There are several reports of hookworm infections that affect school-aged children’s cognitive development and productivity. Children with hookworm anemia have notably decreased scores on cognitive function tests and delayed acquisition of language and motor skills. With treatment of the infection and anemia, their educational performance and productivity improve.
The infection is best confirmed with a stool sample to look for eggs. However, care must be taken to examine the sample within 24hrs so that the eggs do not hatch. The infection can be treated quite easily with anti-helmintic agents, including mebendazole, albendazole, or pyrantal pamoate.
References:
1. CDC. Centers for Disease Control and Prevention. Hookworm Infection. Available at: http://www.cdc.gov/ncidod/dpd/parasites/hookworm/. Accessed May 14, 2006.
2. Hotez PJ, Pritchard DI. Hookworm infection. Sci Am. Jun 1995;272(6):68-74.
3. Hotez PJ, Brooker S, Bethony JM. Hookworm infection. N Engl J Med. Aug 19 2004;351(8):799-807
4. Sakti H, Nokes C, Hertanto WS, et al. Evidence for an association between hookworm infection and cognitive function in Indonesian school children. Trop Med Int Health. May 1999;4(5):322-34. [Medline].
5. Tam, AB. Hookworm. Emedicine. Jan 12, 2007. Available at: http://www.emedicine.com/emerg/topic841.htm
6. WHO. World Health Organization. Hookworm disease. Available at: http://www.who.int/vaccine_research/diseases/soa_parasitic/en/index2.html. Accessed May 16, 2006.
