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Vector-borne diseases in ‘fast pursuit’ of UK

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Despite the UK not having the sandfly vector, cases of leishmaniosis are reported to be widespread

By Josh Loeb

Could leishmaniosis now be considered an endemic disease in the UK?

That sobering question was raised – implicitly at least – by vet Ian Wright from the European Scientific Counsel of Companion Animal Parasites during a talk on vector-borne diseases at the London Vet Show last week.

Canine leishmaniosis, predominantly caused by the protozoan parasite Leishmania infantum, is – officially – not endemic in the UK.

However, during his talk, Wright said there was anecdotal evidence that it is now fairly widespread.

‘I was at another talk the other day and I asked for a show of hands for the number of people that had seen a lyme disease case and everyone’s hands stayed down,’ Wright said. ‘I then asked how many had seen a Leishmania case and half the room’s hands went up – which is quite impressive for a parasite that’s officially not endemic in the UK.’

Asked later by Vet Record whether he thought leishmaniosis should now be classified as an endemic disease in the UK, Wright said: ‘It depends on your definition of endemic, or, strictly speaking, enzootic, since endemic strictly refers to human infection and disease.

‘If the definition is for there to be a stable prevalence of Leishmania-infected dogs in the UK, then the answer is yes. Leishmania infantum infection is currently considerably more prevalent in many UK dogs than other organisms we would consider to be endemic, such as distemper.

‘If the definition requires regular transmission between dogs, then the answer is currently no, but if we continue with the current rate of infected dog importation then it’s only a matter of time before regular transmission in the UK starts to take place as well, even in the absence of the sandfly vector.’

The increasing trend towards stray dogs being rescued and brought into the UK from Leishmania-endemic countries in eastern Europe or the Mediterranean appears to have hastened the spread of leishmaniosis in the UK.

The disease, which is zoonotic, is considered endemic in southern Europe and seasonal in eastern Europe, from where many imported dogs originate.

There have been untravelled cases in the UK...we need to be very, very vigilant for this parasite

‘We don’t have the sandfly vector, but this parasite can be transmitted by venereal and congenital transmission, and now possibly through dog bites, we think,’ Wright added. ‘There have been untravelled cases in the UK – so we need to be very, very vigilant for this parasite.’

In terms of other vector-borne diseases that may in future come to be considered endemic on these shores, Wright said heartworm was ‘in fast pursuit…we’re seeing increased numbers of imported dogs positive for heartworm coming into the UK year on year.’

He also revealed that he has, using extrapolations from surveillance data, calculated that there are now hundreds of thousands of cases of cats and dogs carrying Bartonella-infected fleas in the UK. The figure was based on calculations made using data collected as part of the Big Flea Project, which is run by MSD Animal Health and asks vets to submit flea samples for analysis.

Wright said bartonellosis was a ‘substantially underestimated’ health risk for UK pet owners.

‘This is back of the beer mat calculations, but I make that around about 400,000 cats and dogs that will be carrying Bartonella-positive fleas in the UK,’ he said. ‘This is a very significant zoonosis.’

Summing up the other vector-borne diseases to look out for ‘on our doorstep’ in the year ahead, Wright noted with surprise that ticks carrying the Babesia canis pathogen appear not to have spread much in the UK, despite some ideal ‘tick-spreading conditions’.

‘The Dermacentor tick is the classic transmitter of babesiosis,’ he explained. ‘It’s present right throughout Europe, and it likes to hang out on the beach in the UK. Somewhat unusually, in the rest of Europe it’s more of field tick – it tends to be found more inland. Why it hasn’t spread in the face of wonderful tick-spreading conditions in the UK is a mystery. It’s been found in the same locations for decades in the UK.’

Bizarrely, locations also include the Essex town of Harlow. Asked why Harlow was such a stronghold for this type of tick, Wright replied: ‘It’s one of life’s great mysteries.’

Concluding his run through of vector-borne diseases, he said diseases transmitted by mosquitoes could become a problem in the UK in future as the climate changes.

‘I read in an article recently that the mosquito vector wasn’t present in the UK,’ Wright said. ‘It is very present in the UK. It’s all over the UK. It’s not warm enough at the moment for the parasite to complete its life cycle – but, clearly, that could change.’ •

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