Nature's Design by Richard Thompson

Author:Richard Thompson
Language: eng
Format: epub
Tags: Nature’s Design: Exploring the Mysteries of the Natural World
ISBN: 9781770079670
Publisher: Penguin Random House South Africa
Published: 2011-07-14T04:00:00+00:00

FIV – a benign affliction?

The appearance of an AIDS-like disease in domestic cats and the isolation of FIV-led research workers to cast a wide net in an attempt to identify similar viruses in populations of wild felines. In 1989 Margaret Barr at Cornell University discovered FIV in several captive exotic cats as well as wild panthers resident in Florida. Stephen O’Brien at the National Cancer Institute in Maryland found FIV in a large percentage of African lions. In eastern and southern Africa, it appeared that 80 to 90 per cent of lions were infected, with only the lion populations of Namibia, the Mana Pools region of Zimbabwe and the Umfolozi Game Reserve in South Africa being apparently free of infection – regions largely protected by hostile geographical boundaries. To date, FIV has been found to infect lions, cheetahs, pumas and bobcats, but not tigers or jaguars.

The high incidence of infection seen in lions indicates that FIV is endemic in this species. Both sexes are equally affected. It has been difficult to prove that vertical transmission occurs from mothers to cubs at the time of birth or during breastfeeding, because so few young cubs have been tested. What does seem certain is that most lions are FIV-positive by their fourth birthday. Not surprisingly, scientists were very concerned about these findings – if FIV proved to be as lethal in wild felines as it was in domestic cats, then many species might be threatened with extinction.

Over several years Stephen O’Brien has made a detailed study of the gene sequences of FIV in lions. In this way it has been shown that FIV exists as several variants, each of which is largely restricted to a particular locale. The virus found in the Serengeti is thus slightly different from the one encountered in South Africa. By examining hundreds of blood samples from various cat species around the world, O’Brien came to believe that FIV was an extremely old virus, with origins going back hundreds and perhaps thousands of years. In his view, FIV first appeared in the original ancestral cat species, before this diverged into the many species we see today. This, he believed, explained the wide geographical distribution of the virus. He also put forward the elegant idea that, because of this very long exposure to the virus, there came to exist a form of co-evolution between virus and host in such a way that expression of a full-blown immunodeficiency syndrome had been lost through a process of natural selection. Despite its high prevalence, FIV was to be regarded as essentially benign in wild felines. It was only when the virus infected a similar but unrelated species – such as transmission from a bobcat to a domestic cat – that an AIDS-like disease would be possible, because each type of FIV was species specific. If this theory is correct, it provides reassurance regarding the future of lions and other exotic cats. But is it correct?

Elegant though this theory may be, it does leave many awkward questions unanswered.

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