Question 6- Design a program to eradicate ONE Helminth infestation of humans based on your understanding of that helminth’s lifecycle

Question 6- Design a program to eradicate ONE Helminth infestation of humans based on your understanding of that helminth’s lifecycle

By Gillary Cuartas


References:

Relevant pages- module 7 page 2, 3 and 15-17. and chapter 54 of textbook (4th ed)

There are several types of Helminths mentioned in the notes and text however, I will talk about Hookworm Ancylostoma duodenale which causes hookworm disease.

FIGURE 54-4 Life cycle of Strongyloides species and human hookworm. The invasive filariform larvae penetrate unbroken human skin (1). Once inside the host, migrate through the subcutaneous tissues to the bloodstream (2), enter the lung by crossing into the alveoli (3), travel up the trachea, and are coughed up and swallowed into the gastrointestinal tract (4). The solid line and open arrow (above and to the left of stage 1) indicate that the larvae of the parasite are unable to complete their normal life cycle in a human host. The larvae of Strongyloides and the hookworm mature (5) within the upper gastrointestinal tract. As shown on the right side of the diagram, female hookworm larvae remain within the lumen of the gastrointestinal tract, releasing their eggs into the stool (6), which then pass into the environment (9). Because the female Strongyloides larvae enter the bowel wall, their eggs do not appear in the stool (left side of stage 6), and only the larvae (7) are normally found in the stool. Occasionally, the larvae mature to the filariform stage in the gastrointestinal tract (8) to produce endogenous reinfection (autoinfection). Because hookworm larvae require maturation in the environment to become infectious (9,10,1), autoinfection cannot occur in this disease.



Encounter and Entry

People become infected with hookworms by contact with soil contaminated by human stool and subsequently filled with mature filariform larvae. As they penetrate the skin at the time of initial infection, hookworm larvae may cause local manifestations of itching and irritation (“ground itch”). In human hookworm infections, dermal manifestations are brief and resolve when the larvae enter the bloodstream and lymphatics.

Human hookworm larvae enter the circulation through the bloodstream or lymphatics, traverse the right side of the heart, and become trapped in the lungs. In the lungs the larvae break through the alveolar wall into the alveolar lumen, are coughed up, and are then swallowed into the gastrointestinal tract where they continue their life cycle (Fig. 54-4), primarily in the duodenum and jejunum. Female worms shed eggs into the stool. If the eggs hatch in a warm environment (usually soil in warmer climates), they yield larvae that mature by molting into the infective filariform larvae. That process requires a significant period of incubation outside the human host. Consequently, transmission of hookworms requires contamination of the soil with untreated human feces and subsequent exposure of unprotected human skin to the larvae that develop from the infected feces.Hookworm infection can be prevented by improved sanitation (using indoor or outdoor toilets or treating faeces used for fertilizer) or by wearing shoes. Hookworm infection was common in some areas of the southern United States, where poor sanitary conditions were common until the early part of the last century.



Damage

Hookworms produce chronic anemia by hanging onto the intestinal mucosa with their teeth, secreting an anticoagulant, and sucking the host's blood. That mode of attachment results in a slow, steady blood loss (0.03 mL per worm per day for Necator americanus, and 0.15 mL for Ancylostoma duodenale). Hookworms affect some 800 million to 900 million people throughout the globe; it has been estimated that the total loss of human blood to hookworms is at least 1 million liters daily. The severity of the anemia is proportional to the worm burden. Severe infections in children can produce chronic anemia, which may lead to developmental retardation.

Diagnosis and Treatment

The adult female hookworm releases 10,000 to 20,000 eggs per day into the bowel lumen, which makes it easy to diagnose significant hookworm infections by stool examination using low-power (× 100) magnification. In fact, it is possible to estimate the number of worms pres-ent and the average daily blood loss by quantitating the number of eggs in the stool.

Albendazole, mebendazole, and pyrantel pamoate can be effectively used to treat hookworm infection. Emergency treatment is not required because hookworms produce chronic but not acute or invasive disease. Patients with hookworm disease may require dietary supplementation with iron and folic acid to produce sufficient numbers of red blood cells to correct their anemia.

Another version of Hookworm lifecycle- on CDC, a bit clearer. visit http://www.dpd.cdc.gov/dpdx/HTML/Hookworm.htm

A.duodenale is the second most common human helminthic infection (after ascariasis). Worldwide distribution, mostly in areas with moist, warm climate. Both N. americanus and A. duodenale are found in Africa, Asia and the Americas.A. duodenale is found in the Middle East, North Africa and southern Europe.

SUGGESTIONS FOR DESIGNING PROGRAM:

So there are the facts, the basics you should have picked up are that the best way to prevent hookworm disease due to A. duodenale is to wear shoes and gloves when in contact with soil especially if the soil has been fertilised with feces.

Others- Improving sanitary conditions, using toilets and treating the feces before release into the enviroment, adequate sewerage systems. Those in high risk are children, elderly and gardeners. Remember that a. duodenale can be transmitted via transmammary route. For Australians especially those with cats and dogs it is important to dispose of feces effectively and treat their dogs with appropriate treatment if eggs are observed in the feces. Treating pregnant dogs at later stages in pregnancy can prevent pups from getting hookworm and possibly passing it onto humans. Pups born at home might also benefit from prophylactic treatment.

Education campaigns? Awareness programs – advertising? Improvement of sewerage and sanitation conditions important in developing countries where often toilets aren’t used and floors of homes are still dirt.