Tuesday 27 September 2016

Killer kittens

Whoa! No they don't. Even the Reactograph piece under the clickbait title acknowledges that the rate of  cat scratch fever is about 4 per 100,000 per year, maybe 150 cases across Ireland in 2016. That's about the same as the number of road deaths but the severity of the insult is waaaay different. As an antidote to the nonsense, last Friday Newstalk's Pat Kenny brought a vet onto his daily show to talk about whether we should worry. Said vet said that, after 30 years in the business sustaining scratches on an almost daily basis he's got Teeny's Disease (true dat: if we called CSF by it's alternative name, it might make the headlines less often] just once. It is caused by Bartonella henselae an alpha-proteobacteria some of whom we've met before.

Cat scratch fever is usually found in small children after being inoculated with B. henselae by a cat's claw eeeeuw! Cats don't wash their hands for 20 secs with anti-bacterial soap before or after meals which might be a small bird or a fresh rodent. Bartonella is one of the many species that make a home under their claws. It lives there completely asymptomatic but when introduced to a novel environment like the capillaries of a child, it starts to grow and multiply. In response, the immune system mobilises a swat team of cells and molecules to deal with the invasioners. That systemic mobilisation results in the symptoms: swollen lymph nodes, malaise, headaches, feeling crappy. The bad news is that these symptoms may appears weeks after the causative scratch and as it's the child's first and only experience of Bartonella, you may not make the association. It's her only experience because the next time her primed antibodies make short work of the attackers. Because it's rare, your GP may not recognise it but he'll probably prescribe a broad-spectrum antibiotic and that will  almost always sort everything out. The good news is that, in almost all cases the infection resolves itself in about a month, whether treated or not! It's what your immune system does best. If the infection spreads to the eye then Parinaud's oculoglandular syndrome may result and that's no fun. In a tiny Teeny fraction of cases endocarditis or encephalitis may result and these may be fatal. But for a rare disease, these rare sequelae [rare x rare = minuscule] are not something we need to lose sleep about. The comparative immunology aspects of it - same bug, different response according to host - are quite a lot like Campylobacter: wash your hands if you want, but don't wash the chicken!

When I worked on the population genetics of cats in the 70s and 80s, I'd often get asked to write a piece about my research because kittens are so cute. The publicity manager at U Newcastle upon Tyne asked me to do this for the internal newsletter shortly after I started working there in 1983. His wife had just come through a longish session in ICU after her case of CSF went very wrong. But that's the only serious case that's come at all close to me.

Pat Kenny and the vet went on to discuss another daft headline about drowning all kittens to save the tweety birds. The vet thought this was nonsense, too. Cats may be top-predators [they eat a lot of vertebrates, which eat a lot of invertebrates, which eat a lot of plants but nobody eats them] but they've been around for a long time in Europe and the song-birds have developed effective evasion strategies - they nest up trees and in small holes.  If you kill all the cats around your neighbourhood a) fresh cats will flood in from the surroundings like badgers after a cull and b) you'll get a lot more rodents.  Actually, Dr Vet, it's a bit more complicated than that as noted by Charles Darwin's ruminations on the relationship among the abundance of cats, mice, humble bees and clover. More cats = more clover = more fertile farms = more beef = stronger soldiers = larger empire = god save the queen. The case is altered when cats are introduced to pristine habitats, like Kerguelen Island.

We've had both cats and dogs as pets but they never sat on the sofa, walked over the kitchen table at night or slept in the children's beds. We operate an outdoor shoes off at the door policy and it gives me a small frisson when I see or hear people clunking around in their bedrooms with shoes that have been sampling pavements awash with dog-shit, spittle and the tracks of snails.

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