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expert reaction to study reporting an emerging tick-borne parasite being detected in the UK

Research published in Emerging Infectious Diseases, reports that an exotic tick-borne parasite has been found within sheep in the North of Scotland.

 

Prof Sally Cutler, Professor of Medical Microbiology, University of East London, said:

“The recent report of this protozoa (Babesia venatorum) adds to our increasing knowledge of tick-borne disease risks in the UK, and increasingly recognised Babesia species.  Only a few years ago we saw reports of Babesia infections in dogs from Essex (Babesia canis), and now we have a new Babesia to be aware of.  This example underscores the need to run a full screen of tick-borne pathogens on those individuals falling sick after being bitten by ticks.

Does the press release accurately reflect the science?

“Reasonable account but it has been reported in sheep previously.  Evidence of being more virulent cannot be substantiated at this time.  “Recorded extensively” is too inflammatory.

Is this good quality research?  Are the conclusions backed up by solid data?

“The original article describes detection in Scotland, but only with a geographically limited study.

How does this work fit with the existing evidence?

“Yes, prior detection in companion animal ticks.

What are the implications in the real world?  Is there any overspeculation?

“The finding of this in the UK, as previously with the recent reports of TBE virus, are not too surprising, especially given that migratory birds can carry infected ticks from Europe to UK.

Is it the parasite in a host that has been detected, or the disease in people?

“This reports infection in sheep that have a considerably higher tick exposure compared to people.  It further strengthens the case that humans with disease following tick bites should be screened for a range of tick-borne pathogens to ensure appropriate diagnosis.

How likely is it that people would get the disease?

“Unlikely but not impossible.

Is the disease treatable, and how worried should the public be?

“Previous human cases were successfully treated.  Sensible measures to reduce/prevent tick bites should be used, but no additional precautions beyond this are necessary.”

 

Prof Peter Chiodini, UK National External Quality Assessment Service for Parasitology, said:

Does the press release accurately reflect the science? 

“Yes.

Is this good quality research? 

“This is a sound paper, with good correlation of gene sequences with B. venatorum and clearly visible parasites in the blood films shown.

Are the conclusions backed up by solid data?

“The data justify the conclusions.

How does this work fit with the existing evidence?

“It builds on our previous knowledge of the host range of B. venatorum and now shows it can extend its host range to sheep.

Have the authors accounted for confounders? 

“This is a straightforward description and identification of a known parasite in a new host, so there are no major confounders.

Are there important limitations to be aware of? 

“We do not know how widespread it is in the UK sheep population so longitudinal surveillance is required.

What are the implications in the real world? 

“This parasite is transmitted by Ixodes ricinus, the same tick which transmits Lyme disease in the UK, so the most important precaution is to avoid tick contact.  The necessary measures to do so are described on the TravelHealthPro website.

Is there any overspeculation? 

“The article is measured and does not go beyond the science.

Is it the parasite in a host that has been detected, or the disease in people? 

“This is in a new host (sheep).  Sheep and cattle were studied in this research and only sheep were found to be infected, but B. venatorum has previously been shown to be present in tick vectors in other countries and to infect humans in other countries.

And has the parasite actually been found in the disease-transmitting tick, or just in sheep?

“It has previously been found in the tick in other studies, but not in this one.

How likely is it that people would get the disease from these sheep? 

“People cannot become infected directly from sheep, only from an infected tick vector.

Is the disease treatable, and how worried should the public be? 

“The disease is successfully treated with either quinine plus doxycycline OR with atovaquone plus azithromycin.  The authors only mention B.divergens as being on our radar in British medical practice but they should be aware that UK infection specialists are also accustomed to diagnosing imported cases of B. microti infection.  The public should exercise precautions to avoid tick bites.  If they become unwell in the first six weeks after a known tick bite they should seek medical attention and specifically mention the tick bite.”

 

Prof Paul Reiter, Professor of Medical Entomology, Pasteur Institute, said:

“There is no reason to go overboard with this kind of study – ‘Seek and ye shall find’ is a pertinent mantra.  Part of the reason that these pathogens are ‘emerging’ is that laboratory technology has enabled us to recognise this venatorum from other closely related parasites.

“The important thing is that physicians should be aware of its presence; the parasite is treatable.

“I question whether the parasite has been introduced by migrating birds: the ticks that are the transmitters don’t bite birds.  Much more likely, I suspect, is that infected animals have been imported from an infested area.

“There is no doubt that these tickborne diseases are becoming more prevalent in Europe and in the northern hemisphere.  A key reason arises from deforestation, or rather reforestation of regions that had been cleared in the last few centuries.

“Deforestation is a key to the increasing prevalence of these diseases in Europe and the northern hemisphere.  The pilgrim fathers were plagued with massive numbers it ticks, but these declined as forests were cleared for farming, and hunting decimated the deer populations.  In recent years, reforestation has caused a rapid rise of the deer population and of the ticks that bite them.

“These parasites readily produce mutations that can enable them to infect new host species – so it is no great surprise for the infection to appear in sheep and red deer.”

 

‘Sheep as Host Species for Zoonotic Babesia venatorum, United Kingdom’ by Alexander Gray et al. was published in the journal Emerging Infectious Diseases.

DOI: 10.3201/eid2512.190459

 

Declared interests

Prof Sally Cutler: “No interests to declare.”

Prof Reiter: “No conflicting interests.”

None others received.

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