In Switzerland, an epidemiologist named Charlotte Braun-Fahrländer has found out the following facts based on her asthma survey: Not only were farming children one-third as allergic as their nonfarming rural counterparts, but the more farming they did, the less allergic they were. Children from full-time farming families had half the allergies of those from part-time farming families. And they were one-fourth as likely to have allergies compared with rural children who never farmed. By 2002, numerous studies from around the world had documented "the farming effect."
Without living in a farming environment, pet ownership seems to also have similar beneficial effects. In this article, we will discuss pet ownership and its protective role on our children's health. Note that both dog contacts and cat contacts may provide health benefits . But, dog contacts showed a more significant protective role. So, we will focus only on dogs here.
Dogs are domesticated wolves. They have provided us protection, companionship and hunting assistance since the days of the earliest human settlements. Some recent studies have also shown that pet-ownership to be protective against allergic or infectious disease development.
From one study in Detroit[2,6], researchers examined the effect of having a dog on one indicator of an individual’s tendency to develop allergies: the level of IgE antibodies in the mother’s umbilical cord blood. They have found that pregnant mothers who lived in houses with dogs tended to have lower levels of IgE antibodies in their cord blood—and such lower levels have been found to be protective when it comes to childhood allergies.
Another study of 965 children aged 4-6 years living in rural or semi-rural South Australia was undertaken to investigate the relationship between pet ownership and gastroenteritis in young children. Scientists have found that living in a household with a dog was associated with a reduced risk of gastroenteritis.
In a birth cohort study, 397 children from Finland were followed up from pregnancy onward, and the frequency of respiratory symptoms and infections together with information about dog and cat contacts during the ﬁrst year of life were reported by using weekly diaries and a questionnaire at the age of 1 year. Even after adjusting for possible co-factors, children having a dog at home were significantly healthier, had less frequent otitis, and tended to need fewer courses of antibiotics during the study period than children without dog contacts.
It is now widely appreciated that humans did not evolve as a
single species, but rather that humans and the microbiomes
associated with us have co-evolved as a "super-organism,"
and that our evolution as a species and the evolution of our
associated microbiomes have always been interwined.
-William Parker, Duke University
Endotoxin is a lipopolysaccharide that forms the outer layer of the cell membrane of all gram-negative bacteria. Importantly, it elicits a strong immune response from the mammalian immune system.
Endotoxin levels vary widely but tend to be highest in environments where there are farm animals such as cows, horses, and pigs, because the fecal flora of larger mammals is a major source of endotoxin. Endotoxin is also found in the dust in houses and outdoors in dirt and can be measured in dust or air.
For people living in urban environments, their fingers rarely sink deeply into the mud. Scientists have hypothesized that these people are so deeply removed from the diversity of microbial species that their immune systems fail to develop normally. In such settings, dogs reconnect us to microbial diversity, which may be sufficient to bring sense to our immune system .
Dogs bring bacteria in their mouths, on their skin and in their fur, but also from the dirt around our homes. The links between our bodies and our dogs’ bodies seem to be direct and intimate. A recent study has found that humans tend to pick up, on their skin, some microbes from their dogs. Dog owners tend to share more microbes with their dogs than with random dogs. Evidence has shown that, at least microbially, dog owners really do become more similar to their dogs over time.
Hygiene hypothesis [9,16] proposed to explain this increase in the prevalence of allergic diseases (and maybe autoimmune disease too) is that it results from a decrease in the prevalence of childhood exposure to endotoxin.
By the late 2000s, a revised model had emerged. Soon after birth, a wave of autoimmune cells populated the organism. They helped in defense, anticancer immunity, and tissue repair. A wave of peacekeeping cells quickly followed these initial pioneers, restraining them and establishing equilibrium. But keeping the peace in the long run required more suppressor cells. This secondary squadron emerged only after contact with the outside world—with certain parasites and microbes. It means that our ability to self-regulated, to maintain homeostasis, was oddly reliant on external stimuli.
If we really wanted to fend off allergic disease, the emphasis on the avoidance of allergens is somewhat misguided. Yes, if you're allergic to dust mites, you should avoid them. But if you wished to prevent allergic sensitization altogether, you needed to intercede earlier. The coup de grâce of allergy prevention consists of teaching the immune system tolerance from an early age. How early it should be? The earlier the exposure began, the better. Children who accompanied their parents to the stables during the first year of life had less allergy compared with children who began working on a farm at school age. As matter of fact, even prenatal exposure counts. Indeed, you could predict a child's odds of developing allergy by measuring the endotoxin in her mother's mattress[6,8, 16].
As shown above, recent researches lend support to the health benefits of pet ownership. However, this must be weighed against the potential negative consequences, such as dog bites, particularly for children at young ages. Finally, Karen DeMuth, MD, MPH, has warned that: