Exposure to foodborne and orofecal microbes versus airborne viruses in relation to atopy and allergic asthma: epidemiological study
A decline in orofecal infections and a westernised, semisterile diet may be the root of the epidemic of allergic asthma and rhinitis [inflammation of the mucous membrane that lines the nose] in developed countries, claim researchers from Italy in this week's BMJ.
The theory that some infections in early childhood may prevent atopy [a predisposition to allergic reactions] has been hotly debated and the type of infections that may be involved is still unknown. Dr Paolo Matricardi and colleagues in Rome investigated how exposure to foodborne and orefecal microbes (such as H pylori and the hepatitis A virus) as opposed to airborne viruses (such as measles, mumps and chickenpox) was associated with a reduced prevalence of atopy and respiratory allergies.
Matricardi et al conducted the research of Italian Armed Forces in collaboration with the Consiglio Nazionale delle Ricerche and the Istituto Superiore di Sanit in Rome. They studied 1659 airforce cadets, aged 17-24 years and examined in depth 240 atopic and 240 non-atopic individuals. A history of allergic rhinitis or asthma and sensitivity to airborne allergens was detected. They found that people who had been more exposed to microbes transmitted orally were less likely to suffer from respiratory allergy. However, the same association was not evident in those who had been infected with airborne viruses.
The authors say that this is the first comparative study showing that orofecal and/or foodborne microbes are better candidates than airborne respiratory viruses as determinants of an atopy 'protective' effect. H pylori and Hepatitis A are probably not directly involved in protection from atopy, say Matricardi et al. Nevertheless, the inverse association of atopy with this category of microbes seems to suggest that there is a role played by the gut-associated lymphoid tissue, where microbial stimulation is required to develop immune responses against allergens, they say.
The authors caution that further studies are required to verify their findings, however, it is not inconceivable that we may soon use certain microbes to prevent atopy without causing infectious disease. "We must improve hygiene to reduce the impact of infectious diseases," Matricardi adds, "but at the same time, we must learn how to safely 'train' our immune system, especially during infancy, in order to prevent allergy."
Contact:
Dr Paolo Matricardi, Research Director, Laboratorio di Immunologia ed Allegologia, Divisione Aerea Studi Ricerche e Sperimentazioni, Rome
Email: matricardi.pm@mclink.it