Mr. Mícheál Casey:

Diseases transmitted by ticks are a major cause of economic loss, disease and deaths in farmed animals worldwide. However, Lyme disease is not regarded as a significant economic tick-borne disease in farm animals.

Ticks are not distributed uniformly in Ireland, and even in regions where they occur in large numbers, they have particular habitat requirements. They need shelter from the elements and a moist microclimate which they find in under-grazed farmland and in rough vegetation such as rushes, bracken, and heather. Ticks have some fairly precise environmental requirements, especially when they leave the relative shelter of the base of the vegetation to find a new host. They find a new host by questing, where they climb to the tips of the vegetation and grab onto an animal or person going by. They need mild and moist conditions for questing, which are provided in late spring and in autumn in a typical Irish year. This results in clearly defined spring and autumn peaks in tick-borne diseases. On some farms the ticks have become adapted to one or the other season, while on other farms both peaks are seen. Understanding the type of habitats that ticks favour and the annual peaks of tick activity in spring and autumn is one part of preventing Lyme disease. We know when and where the highest risk of exposure will occur, along with the sub-populations of animals and humans most at risk.

Lyme disease is strongly associated with deer in the USA, whereas in Ireland, research has suggested field mice and some ground-feeding bird species are more important as reservoir hosts. In humans, we know Lyme disease causes a fever and a characteristic skin rash. This can progress to cause central nervous system disease, arthritis and blood vessel damage in humans. In animals, the same is true and the reported cases in the scientific literature worldwide have shown the main clinical signs associated with Lyme disease in animals consist of skin, neurological and arthritic syndromes, with some involvement of muscle.

Research in other countries indicates that this organism is capable of causing sporadic disease in dogs, cattle and horses. No confirmed cases have been reported from Irish animals to my knowledge. However, it is likely there have been occasional undetected cases in animals here, given how common the organism and the vectors are and how commonly animals are bitten by ticks.

There is some evidence that dogs are at higher risk of Lyme disease than other animals. However, this may reflect the amount of time they spend in tick habitats, the number of tick bites they get, and the close attention they receive if they get sick. As they are more likely to be exposed and affected, they are more likely to be detected.

There are many gaps in our knowledge of Lyme disease in Irish animals that need further research in terms of the impact of the organism and the prevalence of Lyme disease in Ireland. This year marks 21 years since barriers to trade in live animals between EU member states were lifted in 1992. It would be timely to survey our tick population to check for the incursion of exotic tick species and to re-survey ticks for the agent of Lyme disease to monitor its distribution.

Having said that, plenty of scientific evidence points towards widespread exposure to borrelia in Ireland. Blood-testing of farmers in Northern Ireland has revealed evidence of widespread occupational exposure to borrelia. This is likely to equally apply to other occupational and leisure users of marginal land and forestry. Surveys that captured and tested Irish ticks have shown that many are carrying borrelia.

Tick-borne diseases of Irish animals occur in well-defined areas and habitats. Within these areas, relatively little tick-borne disease is seen in animals despite apparently heavy exposure to a variety of tick-borne pathogens. This is because the exposure to ticks tends to occur from shortly after birth when the young animal may be protected by maternal immunity passed on in colostrum, the first milk.

Other factors that impact on whether an animal is infected by a tick-borne disease include the phenomenon of co-infection. If a tick is carrying a pathogen, as well as an immunosuppressive disease like tick-borne fever for example, then the chances of that pathogen causing disease are increased. Many of the animal tick-borne diseases depend of these cold infections with tick-borne fever to cause the pathogen to multiply.

Prevention of tick-borne diseases in animals consists of preventing and reducing the risk of tick bites. Preventive treatment of animals against ticks is commonly employed in high risk areas to kill ticks or to prevent the organism from multiplying in the animals. These measures are probably controlling tick numbers on animals and may be preventing us from seeing more Lyme disease in Irish animals, but Lyme disease is not the reason for applying these treatments. Rather, it is for other tick-borne diseases such as Redwater and Louping-ill and other such diseases.

Treatment is reported in literature to be straightforward, with antibiotic treatment in the acute phase. The important thing is awareness from an animal point of view and ensuring veterinary practitioners are aware of the possibility of Lyme disease as a differential diagnosis when dealing with an animal showing suggestive clinical signs. This is an area where information campaigns and continuing education can increase the awareness and responsiveness of veterinary practitioners to possible cases.