Zoos exist to save people money spent travelling to exotic places to see animals in the wild. By bringing a large number of species together in a small space people get a snapshot of the world’s different biomes. Pity the archaeologists of the future digging through the remains of Melbourne, Los Angeles and London, wondering how elephants, tigers and monkeys could have been native to all three cities.
While it’s certainly “nice” to see polar bears in Melbourne, they don’t appreciate the summer heat any more than the gorillas in Toronto enjoy the snow. This mixing and matching produces all sorts of husbandry and dietary problems, which are handled with varying degrees of success. It also creates novel disease issues. This was highlighted recently by the deaths of four polar bears in a German zoo (Greenwood et al 2012). They died of a herpesvirus infection contracted from the zoo’s zebras. The herpesvirus was perfectly well adapted to the zebras and caused them no problems but, when it got into a naïve, non-adapted polar bear, fatal illness was the result.
Herpesviruses seem particularly good at this sort of thing. African elephants carry a herpesvirus that is fatal to Asian elephants. Wildebeest carry a herpesvirus that kills other species of hoofstock. Squirrel monkey herpes kills owl monkeys. A herpesvirus carried by South American conures kills African and Australian parrots. SIV, a relative of HIV (and not a herpesvirus) carried by African monkeys, kills Asian macaques. Normally this would not be a problem as these animals, and their bugs, would not come in contact with each other. However, this mixing of animals from different areas, which gives adapted viruses and bacteria access to non-adapted hosts, is occurring more and more.
Not only is this a problem in zoos but it is happening in the big wide world too. As we clear more and more habitat we come into contact with new species and new disease agents. Feral species, which have made their way into new habitats because of our deliberate or accidental influence, bring their bugs with them too. Species that previously had no connection with each other are suddenly brought into close proximity. Hence, the transmission of Hendra virus from bats to horses, Nipah virus from bats to pigs, toxoplasmosis from feral cats to marsupials and otters, monkeypox from Gambian giant rats and prairie dogs to humans, and chytridiomycosis from African clawed frogs to the amphibians of the world.
At least, when animals are concerned, some of these diseases can be confined to farms or contained by quarantine measures. These are, however, not always as effective as we would like as seen by the introduction of foot and mouth disease to Great Britain, equine influenza to Australia, and psittacine pox to New Zealand. These diseases were eradicated at great expense and effort.
Unfortunately people don’t go through quarantine when they travel, allowing for extremely rapid dissemination of diseases. Just look at how quickly SARS spread from South East Asia in November 2002 to Canada by April 2003. It is estimated that a flu outbreak in the northern hemisphere will reach Australia in four to eight weeks. While we impose travel restrictions on animals to safeguard our pets and agriculture we certainly don’t want to inconvenience ourselves by impeding our own travel, even though the consequences are potentially far more catastrophic. While globalization has facilitated trade, democracy, entertainment, and the dissemination of information, it has also greatly enhanced our ability to spread disease. Unfortunately the science of predicting what the next possible pandemic will be and where it will come from is at a similar stage as the science that predicts earthquakes and volcanic eruptions i.e. we have absolutely no idea. For the moment all we can do is react and hope that will be enough.
And don’t forget to keep washing those hands.
Dr. F. Bunny
Greenwood, A.D., K. Tsangaras, S.Y.W. Ho, C.A. Szentiks, V.M. Nikolin, G. Ma, A. Damiani, M.L. East, A. Lawrenz, H. Hofer, and N. Osterrieder. 2012. A potentially fatal mix of herpes in zoos. Current Biology http://dx.doi.org/10.1016/j.cub.2012.07.035.