International trade in wildlife is a likely factor in the spread of animal-human diseases, and has the potential to increase the risk of outbreaks in the near future.
Speaking at a symposium on human health and emerging infectious diseases at the Diversitas: Biodiversity and Society conference in Cape Town last year, scientists identified the increasing global trade in wildlife carrying potentially harmful diseases as a driving factor for outbreaks.
Dr Katherine Smith, Assistant Professor of Biology at Brown University, Rhode Island, United States, described the increase in human-induced spread of disease to other parts of the world as “pathogen pollution.”
“It’s a relatively new term for a process that’s been happening as long as people have travelled,” she said.
But because of the increase in people travelling in modern times, and the greater speed and distances involved, the process has been greatly accelerated since about 1940.
Human diseases tend to be found in most countries as a result of travel, whereas zoonotic diseases (those transmitted from animals to humans) aren’t yet nearly as globalised, suggesting that they have room to expand.
Of infectious diseases that have emerged in the last hundred years, 75% have been zoonotic (including HiV/AIDS, SARS, Ebola and H5N1 avian influenza), and scientists warn that we should brace ourselves for more.
Craze for exotic pets
A major area of concern is the international trade in wildlife: there is huge demand for exotic pets, imported mainly from the third world to the first. In just six years, said Smith, 1,5 billion live animals were exported into the United States alone.
“That works out to an average of five pets per American citizen,” said Smith.
Of these exotic animals, which came from many different parts of the world, 73% had been wild caught, and the vast majority were sold commercially.
About 70% come from South-East Asia, which, significantly, is also considered to be a “hotspot” for future zoonoses.
Exotic fish comprise a high proportion of the animals transported, to meet the demand created by aquarium and ornamental pond owners.
However, said Smith, “Just about everything else gets imported too – mammals, reptiles, amphibians. There’s been increased demand for reptiles as pets recently, perhaps as a result of people seeing them on popular nature programmes on the Discovery Channel.”
Tokay geckos can transmit salmonella to their human owners.
When Smith and her team examined 30 Tokay geckos, a species on the rise as a popular pet import from Indonesia and South-East Asia, they found that 60% had Salmonella, which humans can get from close proximity with reptiles. Not only were a high percentage of the animals infected, but they also exhibited a large number of Salmonella strains, many of which are more commonly associated with livestock.
"It turns out," said Smith, "that in Indonesia these geckos are about as common as pigeons, and especially so around human habitation and livestock. The geckos, people and livestock in close proximity encourage parasite transmission, and its from these areas, where it's easier to catch the geckos, that most of the imported pet geckos come."
Another popular recent trend spurring imports is the demand for exotic “pocket pets”, small “cute” animals that can be easily held in the hand or carried in a pocket.
One such pocket pet species, the Gambian pouched rat, was cited during the symposium as a prime example of how the industry is set up to facilitate the emergence of infectious disease.
In 2003 there was an invasion into the Florida Keys by pouched rats, accompanied by an outbreak of monkey pox – never before seen in the U.S. – that affected 72 people. The source was identified as “Phil’s Pocket Pets” in Illinois, where infected pouch rates had been stored in close proximity to prairie dogs (also kept as pets.) The disease spread to the human owners of both these rodent species.
Gambian pouched rat.
Adding to the concern about disease spread is the fact that the large number of wild animals moved across borders and between continents is poorly regulated in most nations. Exceptions to this are Australia and New Zealand, which exercise strict control over movement of organic material to or from their countries.
Public health experts recommend much tighter customs and border controls on exotic species, said Smith.
A serious obstacle to instituting better regulations is opposition from the pet industry itself, which has considerable lobbying power in many countries and can demonstrate the economic benefits of wildlife trade. Also, it is often hard for scientists to prove that an animal poses a high enough human health risk to warrant banning its importation.
Dr. Peter Daszak, Executive Director of the Consortium for Conservation Medicine at Wildlife Trust, New York, believes that one of the ways to better control the wildlife trade is to promote captive breeding of commercially important animals.
Animals in captive breeding stations have been shown to have lower levels of disease-causing pathogens, and locally-bred animals would reduce the demand for imports.
(- Olivia Rose-Innes, Health24, updated April 2010)