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Speaking at BSAVA congress, Ian Wright, Head of ESCCAP, claimed that some of the parasites that have recently emerged as threats in the UK have been ‘genuinely surprising’. It’s not just the emerging parasites like Linguatula serrata (the tongue worm) we need to prepare for, existing parasites are evolving too. New vectors and increases in population size and distribution mean that the recommendations given to clients may have to be reassessed based on the most current information.

Our understanding of parasite threats is also changing in the light of new data. Babesia canis previously did not exist in the UK and is now endemic. Parasites such as Bartonella henselae, Toxocara cati and Rickettsia felis are now known to be much more common than previously thought and represent a significant zoonotic threat. Of the existing parasites, Ixodes ticks are increasing in number, thereby increasing infection pressure, and Angiostrongylus vasorum (lungworm) has expanded its distribution, spreading across the UK into areas where, even eight years ago it was not found.


The tick risk and Lyme

More ticks and more time spent in the great outdoors may account for the recent finding that one in every three dogs hosts at least one tick1 with many hosting multiple ticks. The picture is still very much one of focal distribution in high prevalence areas, but we are seeing larger populations, of which around 89 per cent are the species Ixodes ricinus1. Nymphs and larvae are the most important life-stages in transmission of Borrelia burgdorferi - the bacteria that causes Lyme disease. At just 1-2 mm long these tick life-stages are difficult to spot. Although less than three per cent of ticks are found to carry Borrelia burgdorferi2, exposure to larger numbers of ticks may mean that in fact the risk is much greater.

The characteristic ‘bulls-eye rash’ sometimes seen after infected ticks bite people is not seen in dogs – and in fact doesn’t appear in two thirds of people. Cardiac disease remains a rare complication, and in the UK Lyme nephritis is not recognised in dogs – renal involvement can occur, but not on the same acute scale as seen elsewhere. Serology is the most useful diagnostic test and taken with relevant clinical signs a positive result should prompt treatment. A minimum of four weeks doxycycline given at a dose of 10 mg/kg is indicated.

Removal of ticks within 24 hours, before transmission is likely to take place, should be advised in endemic areas. Despite the availability of products which can repel, or rapidly kill, no product is 100 per cent effective in protecting against the effects of tick bites. When making recommendations it should be considered that frequent daily walks in low risk areas may actually present greater exposure to ticks overall than infrequent walks in high risk areas.


Emerging tick risks

Babesia canis is transmitted by the Dermacentor reticulatus species of tick and the Essex cases reported last year were in dogs that had not travelled abroad. There can be fatalities - mainly in cases that are missed, treated late or are particularly severe. A blood smear from a peripheral blood vessel, usually the ear, will allow identification of the typical paired piroplasms. Imidocarb is the treatment of choice and the aim is for remission. Survivors may experience relapses and will need tick protection for the remainder of their lives.

Rhipicephalus sanguineus is mainly found in southern Europe and is brought in on imported dogs. This tick species can reproduce indoors and can be very hard to eliminate – taking up to a year of repeated fumigations in some cases.

Tick borne encephalitis (TBE) is also ‘rampaging across Europe’ and as the Ixodes vector is present in the UK this could be especially serious if it becomes endemic. According to the NHS around one in every 100 people who developed symptoms of TBE will die of the condition. Ian recommends that all imported dogs are checked thoroughly for ticks.


Lungworm – genuinely on the move

Angiostrongylus vasorum has expanded from foci in the South East and Wales across the whole country and is ‘genuinely on the move’. Foxes have been implicated in the spread and the prevalence in foxes has increased from 7.3 per cent to 18.3 per cent in the past eight years3,4. Spread tends to occur in ‘hot spots’ often influenced by climate (warm and wet) and increased snail, slug and fox numbers. Infected dogs moving into new areas may also be a factor. A new focus will tend to either establish or drop away again but overall the parasite is here to stay, it is spreading and the situation is unlikely to improve.

Monthly treatment is recommended to control lungworm and in high prevalence areas is essential. Being aware of new cases in the area and in other practices, along with the lifestyle of the pet can help form practice protocols in areas where the parasite is not currently thought to be established.

Coughing is the predominant clinical sign to be aware of in practice. A patient side test (Idexx Angio Detect™) provides a useful screen and delivers results within 15 minutes. Testing every coughing dog and every bleeding dog for one month would provide a useful snapshot of the practice situation. Previous exposure doesn’t provide any immunity and a history of eating snails, slugs or frogs, or eating grass (which could contain tiny snails or slugs) indicates a need to treat.


New threats from familiar parasites

It’s recently been identified that 26 per cent of cats are infected with Toxocara cati5 and are excreting eggs, making them the most significant contributors to environmental contamination with the parasite6. This is particularly the case with stray cats. As cats bury their faeces in soil or sand, the eggs are protected from sunlight and therefore survive for longer. Toxocara is a significant zoonotic risk, especially for children. Regular monthly treatment should be considered for cats in households where there are children, elderly people, or immunosuppressed individuals, such as those who have had a splenectomy or organ transplant.

The tapeworm Echinococcus granulosus is another potential zoonosis, causing hydatid cysts in the liver, CNS or bone. Dogs that eat raw diets or consume unsalvaged carcases are at risk. There are hotspots of activity reported from abattoirs in Wales and the Western Isles in Scotland, but cysts are being increasingly reported in abattoirs around the country. Dogs at risk should be treated with a suitable anthelmintic every four to six weeks and those fed raw diets should be treated at least four times per year as a precaution.

Cat scratch disease is caused by Bartonella henselae and transmitted through flea faeces. More than 40 per cent of cats have been exposed and as soon as there is flea dirt on a cat there is the potential for humans to be exposed. People are infected through cracks in skin so barrier hand protection can be beneficial in reducing the risk of infection. Rickettsia is also a zoonosis and 6-12 per cent of cats carry Rickettsia felis7. No vector is needed and rickettsia can be transmitted directly between fleas. Both provide compelling reasons to recommend regular flea control.


Assess and evaluate the risks

The speaker concluded his talk by reminding delegates how the parasite scene changed during 2016: as well as multiple cases of disease due to Babesia canis in Harlow, and later Romford, the UK saw its first recorded cases of Dirofilaria repens, Thelazia callipaeda (eye worm) and Linguatula serrata (tongue worm). He reminded vets that these parasites have zoonotic potential and noted that cases of leishmaniasis and ehrlichiosis also increased in the same year.

Thorough checks of imported animals, removal of any ticks they host and repeated tapeworm treatments, even if the animal has been treated before travel, are advised. Increasing awareness of the parasites that might be presenting a greater or new risk is vital, as is making a recommendation in the light of current evidence to help protect the health of pets and people.


References:
  1. Abdullah (2016) Parasites &Vectors, 9:391
  2. Smith et al. (2012). Comparative Immunology, Microbiology & Infectious Diseases 35: 163–7
  3. Morgan et al. (2008) Vet Parasitology 154, 48-57
  4. Taylor et al. (2015) Parasitology 142 (9) 1190-1195
  5. Wright et al. (2016) Journal of Small Animal Practice 57 (8) 393-395
  6. Nijsse et al. (2015) Parasites & Vectors 8:397
  7. Kenny et al. (2003). Emerging Infectious Diseases. 9(8): 1023–1024.
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