Does Hepatitis A Offer Protection against Asthma or Does Asthma Offer Protection Against Hepatitis A? pp. 1-9
Authors: (Lars-Georg Hersoug, Research Centre for Prevention and Health, Copenhagen County, Denmark, Jose Arnau, Unizyme Laboratories, Denmark)
Abstract: In several studies, primarily from developed countries, an association between hepatitis A virus (HAV) and atopic diseases, including asthma, allergic rhinitis, and atopic dermatitis has been found. Whereas such an association has not been found in other studies, but thise studies primary came from underdeveloped countries. The finding that being seropositive to HAV is associated with a lower prevalence of atopy and respiratory allergies has been interpreted as HAV infection protecting against atopy. But this assumption can only be true if the HAV infection precedes the establishment of the atopic phenotype. If the atopic phenotype precedes the HAV infection, then the opposite assumption must be true i.e., it is the atopic phenotype that protects against HAV infections. An HAV infection is of short duration, and the virus is permanently cleared from the body. The finding of an association between atopy and HAV was taken as an indirect evidence for “the hygiene hypothesis”. Recently, by studying different polymorphisms in the TIM-1 allele and their interactions with HAV it was argued that a special insertion variant in combination with HAV infection protects against atopy and that this was the first genetic evidence for the hygiene hypothesis. In this study, we discuss these findings and show that the interaction with HAV and the TIM-1 alleles cannot be taken as a genetic evidence for the hygiene hypothesis. Because atopy and the TIM-1 alleles are not independent variables, the argument, that the insertion variant in combination with HAV infection protecting against atopy, is not valid. Additionally, despite epidemiological findings of an interaction between HAV infections and atopy there is not necessarily a causal relationship to the development of atopy. Indeed, the opposite assumption could be true, that the atopic condition protects or is associated with mechanisms that protect against HAV infections.