Wednesday March 23 2011
Ticks carry a number of diseases including Lyme disease and tick-borne encephalitis
“A breed of blood-sucking tick normally found on the continent has been discovered in Britain for the first time,” reported the Daily Mail. It added that scientists say climate change has brought the parasite to the UK, and warned that it may have brought new strains of disease from Europe.
The story is based on a cross-sectional study that monitored tick infestations in more than 3,500 dogs taken to veterinary practices in Great Britain. The study found that on average, 15% of dogs were infested with ticks which, according to the researchers, is far higher than previously recorded.
One type of tick found was the European meadow tick (Dermacentor reticulatus). The authors say it adds to growing evidence that this tick population now exists in southeast England. In Europe, this tick is an important carrier of a serious disease in dogs called canine babesiosis.
This research is one of the few studies to monitor tick infestation in domestic dogs in Great Britain. It suggests that many more dogs are carrying ticks than previously thought, and that infestation may go unnoticed by their owners. This may have important implications for human and animal health, and for the potential transmission of tick-borne diseases such as lyme disease and tick-borne encephalitis. However, it is uncertain whether the prevalence of ticks in dogs being taken to veterinary practices represents their prevalence in the general UK dog population. It is possible that dogs seen by vets are more likely to have tick infestations and are taken to the vets by their owners with corresponding symptoms.
Where did the story come from?
The study was carried out by researchers from the University of Bristol and from Merial Animal Health Ltd, a company that develops treatments for animal diseases. It was funded by the Natural Environment Research Council and Merial.
The study was published in the (peer-reviewed) journal Medical and Veterinary Entomology.
The study was covered accurately by the newspapers, although reports that a “breed of bloodsucking tick” normally only found in continental Europe had been found for the first time in the UK may be slightly alarmist. All ticks, whether native to Britain or not, suck blood. Also, as the researchers point out, there is evidence that populations of these ticks already exists in parts of the UK.
Although climate change was suggested as a possible cause of the increase in tick infestations, this study did not look at any association between climate and tick infestations.
What kind of research was this?
This was a cross-sectional survey of 173 veterinary practices in Great Britain, involving a randomised sample of dogs, to establish the prevalence, type and distribution of ticks on domestic dogs in Great Britain.
The researchers point out that ticks are second only to mosquitoes in transmitting disease to humans and animals. They say that there is growing concern over the distribution of ticks, the potential impact of climate change, and the increased movement of people and their pets between countries. Recent studies suggest that tick prevalence is increasing in the UK. Those that pose a particular threat to dogs are the sheep tick (Ixodes ricnius) and the hedgehog tick (Ixodes hexagonus).
What did the research involve?
The researchers contacted 173 veterinary practices in England, Scotland and Wales, and asked them to monitor tick attachment to dogs in their local areas, between March and October 2009. Each week, over a two- or three-month period, the practices randomly selected five dogs from those brought to the surgery and gave them a thorough examination for ticks. Samples of any ticks found were sent to the researchers for identification, along with a clinical history of the dog.
Each practice was provided with questionnaires, sample pots, and a tick survey kit with a standardised grooming protocol to detect ticks. At any one time, 60 practices were involved in the survey, with each practice participating for three months before being replaced.
The researchers used standard statistical methods to calculate the distribution of tick infestation, the risk at different times of the year, the risk for different dog breeds and the prevalence (proportion of cases at any given time).
What were the basic results?
A total of 3,534 dogs were examined, and 810 dogs were found to be carrying at least one tick, although the number of ticks ranged from 1 to 82. Nearly 63% of these were from rural practices, and just over 37% from urban ones. Twenty-five of the practices found no ticks, while 19 reported that more than half the dogs inspected carried ticks.
The main findings:
- Over 72% of the ticks were sheep ticks and nearly 22% were hedgehog ticks. Five cases of the European tick, Dermacentor reticulatus, were also found in West Wales and south-eastern England.
- Gundog, terrier and pastoral breeds were more likely to carry ticks, as were non-neutered dogs.
- Dogs with shorter hair were less likely to have ticks.
- Dogs were most likely to carry a tick in June and least likely in March.
- The average frequency of tick infestation in all dogs examined between March and October was nearly 15%.
How did the researchers interpret the results?
The researchers say that their study gives a tick prevalence in dogs that is higher than previously recorded in Britain, both in urban and rural environments, although they do not specify how much higher. This has important implications for the potential transmission of tick-borne disease, not only in dogs but also in humans.
The identification of five samples of D. reticulatus in eastern England and also western Wales, was notable, they say, supporting a growing body of evidence that these ticks are established in southeast England.
Ticks are known to carry various diseases, including Lyme disease, which can affect humans as well as other animals. The value of this study lies in the fact that it used a large randomised sample of dogs from across the UK to assess tick infestation. However, it is not certain whether the prevalence of ticks among dogs seen in veterinary practices is representative of the prevalence in the dog population as a whole. It is possible that dogs taken to the vet are more likely to have ticks and to be showing symptoms.
Also, as the researchers note, data from 43 practices was removed from the analysis of prevalence because there was a possibility that veterinary staff had misunderstood the protocol. The researchers consider 43 to be a small number of practices, but they represent almost a quarter of the practices recruited and their removal could have affected the findings on prevalence.
In conclusion, this is a valuable study that was carefully carried out, using a randomised sample of dogs. It suggests that tick prevalence in dogs may be on the increase, and that many dogs carry ticks without their owners’ knowledge. Despite its limitations, these findings could have important implications for both human and animal health.
Ticks can spread a number of diseases, including Lyme disease in humans. This is an inflammatory disorder, which can become chronic if left untreated. Lyme disease is caused by a bacterium which the tick carries and can acquire up from biting infected deer or other wild animals. Humans can get the disease if they are bitten by an infected tick.