About Ticks & Tickborne Diseases
Ticks are blood sucking ectoparasites that require a suitable host to complete their lifecycle. There are at least twenty species of ticks indigenous to the UK, with the most common being Ixodes ricinus. This tick is more commonly known as the sheep tick and is the vector for a number of diseases which affect livestock such as louping ill, tickborne fever (TBF), babesiosis (redwater fever), and tick pyaemia. However the same ticks can transit Lyme disease (Borrelia) as well as louping ill and tickborne fever to humans, dogs and horses. The sheep tick is distributed widely all over the UK but prefers dense vegetation and warm, wet conditions to support the free living stages of its life cycle.
There is increasing awareness of ticks and tickborne diseases, amidst reports of ticks spreading geographically and increasing in numbers. Factors which may contribute to this are:
- Climate change; in particular relatively wet summers
- Sheep farming economics and a reduction in sheep dipping
- Environmental biodiversity management strategies in relation to habitat
- The marked increase in deer numbers acting as tick maintenance hosts
Upland grazing is the preferred habitat of the sheep tick. Tick infestations are therefore of significant importance to hill sheep production with animal welfare concerns resulting from irritation, anaemia and risk of disease transmission; and economic loses resulting from disease outbreaks. Tick infestations are also a public health concern due to the risks and effects of Lyme disease and other zoonotic diseases.
A summary of each of the diseases mentioned above can be found in the further information section below.
- Ticks are blood sucking ectoparasites that require a suitable host to complete their lifecycle.
- There are at least 20 species of ticks indigenous to the UK, the majority only parasitising specific wildlife hosts. The sheep tick however is non-specific.
- Ticks are spreading geographically and increasing in numbers, most likely because of climate change.
- Ticks are inactive in a cold winter and only start looking for a host when the mean weekly temperature exceeds 7oC.
- Ticks have a three year life cycle (or longer) with each stage requiring only one blood meal (one host).
- The three host life cycle of sheep ticks makes it possible for them to transmit diseases to their host during both the later-stage blood meals (nymph and adult).
- The most common tick in the British Isles is Ixodes ricinus, the sheep tick, which is the vector for the five diseases listed below.
- The important diseases transmitted to livestock by ticks in the UK include: louping ill, tickborne fever, babesiosis (redwater fever) and tick pyaemia. However the same ticks can transmit Lyme disease (Borrelia), louping ill and TBF to humans, dogs and horses.
- Louping ill is the most common disease of sheep spread by ticks in the UK. Louping ill also causes severe losses in red grouse, however cases of louping ill in dogs, horses and humans are rare.
- Tickborne fever is prevalent where sheep and ticks are common and sheep intended for breeding should be exposed to ticks prior to mating for the first time. The most common sequelae of tickborne fever are abortion and immunosuppression.
- Tick pyaemia affects lambs (2-12 weeks old) and causes significant economic loss through debilitation and death. The main symptoms are weakness, severe lameness and paralysis.
- Tick control should be planned for individual farms as part of flock health plans in consultation with your vet.
- Generally, for most sheep flocks in high risk areas, acaricides are the main form of control.
- Lyme disease is a zoonotic disease which can be treated if diagnosed quickly.
- All farmers, gamekeepers and those who use the countryside for recreation should be aware of the symptoms of Lyme disease.
Research on Tickborne Diseases at Moredun is a recent development and is directed, in the first instance, to the development of a number of diagnostic tests to increase our disease-detecting capabilities.
Currently the Virus Surveillance Unit carry out serological (disease surveillance) and molecular (diagnostic) test for louping ill and TBF (molecular diagnosis only). Tests in development include a serological test for TBF, a molecular test for Lyme disease, and the possibility to test simultaneously for all three diseases in the same sample, enabling the identification of coinfections. More information on the tests and the samples required can be found on the Surveillance page.
In addition, we are developing protocols which will enable the same tests to be carried out directly on ticks which will complement the work on tick distribution and deer density in different ecosystems currently taking place at the James Hutton Institute (in collaboration with Prof. Lucy Gilbert).
In collaboration with Nottingham University (Prof. Janet Daly) we are looking at cutting edge molecular techniques to characterise the antibody response to the louping ill virus with the aim of identifying specific sequences which will be used to improve the tests currently performed.
In collaboration with Glasgow University (shared BBSRC PhD) we are looking at the genetic mechanisms which allow different members of the tick-borne encephalitis sub-group of the genus flavivirus to infect a variety of different hosts, and their species-specificity.
We are in receipt of Scottish Government funding (RDs 2.2.2 and 2.3.3 of the Strategic Research Programme) for the development of diagnostic tests and the collaborative work with the James Hutton Institute.
The collaboration with Glasgow University is a shared, BBSRC-funded PhD whereas the collaboration with Nottingham university is carried out through a Moredun/Nottingham shared PhD.
The most common tick in the British Isles is Ixodes ricinus, the sheep tick, which is the vector for the following five diseases:
Louping ill is a tick transmitted acute viral disease affecting the central nervous system and principally found in sheep but also occasionally causes disease in humans, cattle, horses, goats, dogs, pigs, red grouse, llamas and alpacas. Ticks become infected when they feed on a host which is undergoing an active infection with virus circulating in the blood (viremia). The virus establishes in the salivary gland of the tick, where it can remain from one year to the next, and is injected into another host when the tick feeds again.
In areas where louping ill is present the mortality rate is 5-10% and occurs typically in animals less than 2 years old. Initially animals develop fever accompanied by depression and lack of appetite. Later, during the sub-acute phase of the disease, muscule tremors often develop; seizures, paralysis, coma and death can also occur.
Please see our louping ill best practice booklet for more information.
Tickborne fever (TBF)
Tickborne fever in sheep is caused by the bacteria Anaplasma phagocytophilum and the disease severely depresses the immune system, even if little or no symptoms are present during the initial infection. It therefore leaves the animal predisposed to further secondary diseases. For example tickborne fever in lambs can lead to a more severe manifestation of louping ill, tick pyaemia and respiratory disease. Abortions observed during outbreak of ticjborne fever are mainly related to high fever and can occur at any stage of pregnancy.
Tickborne fever is prevalent wherever ticks and sheep are present. All ages of animal are susceptible and maternal antibody in colostrum provides no protection. Clinical signs include: a sustained high temperature, loss of appetite and depression.
Cattle and deer rarely show clinical signs of disease but may act as reservoirs of infection.
Tick pyaemia typically affects lambs between 2 and 12 weeks of age and results in the formation of abscesses in various parts of the body, mainly in the joints, tendon sheaths, and muscles. These abscesses cause debilitating lameness and paralysis hence the common term “crippled lambs.” The disease is enzootic (permanently present) in many regions of the UK where the sheep tick is common.
Redwater fever (babesiosis)
Transmitted by the sheep tick, this cattle disease is caused by a protozoan parasite (Babesia divergens) that infects the red blood cells. Though widely distributed where ticks and cattle are present, generally it is not a serious problem as cattle under nine months of age do not develop clinical disease following infection, and become solidly immune.
A resident herd of cattle will seldom experience disease problems and it is only when older susceptible animals are introduced to a tick infested area for the first time, or ticks encroach into new areas, that disease occurs.
Lyme disease is an important zoonotic disease of public health concern. The disease is transmitted by the bite of a sheep tick infected with the bacteria Borrelia burgdorferi. The disease can be found over most of the UK although it is more prevalent in areas with high tick populations such as the Scottish Highlands, Exmoor and the Yorkshire moors.
If you suspect Lyme disease, talk to your GP as soon as possible. Additional information can be found on the NHS website.