Cholera: disappointing vaccine performance could be caused by worms

16 Apr 2009

Paul Chinnock

Source: PLoS Neglected Tropical Diseases (see original article)

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Hookworm, and other worm infections, appear to reduce the effectiveness of cholera vaccines.
WHO.

Cholera vaccines have generally been found to deliver a disappointing performance in the field. For example, one vaccine produced a 90% rate of seroconversion (indicating protection) in over 90% of North American and European adult volunteers who were given one dose of the vaccine. However, when given to children in an area of Indonesia endemic for cholera, a rate of only 16% was achieved.

Cholera occurs mostly in impoverished areas where there is poor sanitation and intestinal parasites are also common. It has been suggested that co-infection with intestinal parasites may affect the immune responses to Vibrio cholera, the disease agent responsible for cholera. This hypothesis has been investigated at ICDDR,B (the International Centre for Diarrheal Disease Research in Bangladesh) which treats an estimated 20,000 cholera patients every year.

Scientists from ICDR,B and from the USA conducted tests on 361 patients in Dhaka, Bangladesh, of whom 53 had intestinal worm infections – mostly roundworms, hookworms and tapeworms.

The researchers found that cholera patients with parasitic worms had decreased antibody response to cholera toxin. The decrease was greatest in the IgA antibodies, which are secreted in the intestine. However, patients with worm infection did not have a difference in their immune response to lipopolysaccharide, a sugar-based molecule that is important for immunity. These different effects on the immune response to cholera toxin and lipopolysaccharide could be explained by the effect of parasitic infection on CD4+ T cells, a type of cell that influences the development of the antibody response to proteins such as cholera toxin but may not always influence the response to sugar-based molecules.

The finding that worm infection is associated with decreased immune responses to cholera provides an additional reason for deworming in cholera-endemic areas.