A paper published in this week's PLoS Medicine shows that vaccination against a protein secreted by the dog hookworm can protect against blood loss and anaemia caused by the same hookworm in dogs. The researchers, led by Alex Loukas and Peter Hotez, showed that vaccination of dogs with recombinant Ac-APR-1, an enzyme that starts the digestion of hemoglobin in hookworms, induced an immune response and resulted in significantly reduced hookworm burdens and fecal egg counts in vaccinated dogs compared to control dogs after challenge with infective larvae of the hookworm Ancylostoma caninum. Most importantly, vaccinated dogs were protected against blood loss and most did not develop anemia, the major result of hookworm disease.
Hookworms are intestinal parasites of mammals, including humans, dogs, and cats; in humans these infections are a leading cause of intestinal blood loss and iron-deficiency anemia. Hookworm infections occur mostly in tropical and subtropical climates and are estimated to infect about 1 billion people worldwide-- about one-fifth of the world's population. People who have direct contact with soil that contains human feces in areas where hookworm is common are at high risk of infection; because children play in dirt, they are at the highest risk.
These results set the stage for the next stage of vaccine development in humans. Loukas and colleagues suggest that the ideal hookworm vaccine would be a mixture of two recombinant proteins, targeting both the infective larva and the blood-feeding adult stage (as targeted here) of the parasite. Such a vaccine would limit the amount of blood loss caused by feeding worms and maintain normal levels of hemoglobin.
Citation: Loukas A, Bethony JM, Mendez S, Fujiwara RT, Goud GN, et al. (2005) Vaccination with recombinant aspartic hemoglobinase reduces parasite load and blood loss after hookworm infection. PLoS Med 2(10): e295.
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