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Rise in tick populations poses threat

Ticks can add additional challenges to farm environments in many parts of the UK. With reports of populations of the ectoparasite on the rise, Laura Bowyer reports.

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Ticks are blood sucking ectoparasites with at least 20 species indigenous to the UK, most only parasitising specific hosts.


Dr Mara Rocchi and Dr Hugh Reid at Moredun Research Institute have looked at ticks and tickborne diseases in livestock with the Royal (Dick) School of Veterinary Studies, University of Edinburgh, and say numbers in the UK are increasing.


Dr Rocchi says: “Many areas of the British Isles are affected by ticks and tickborne diseases of livestock, with ixodes ricinus being the most common. Tick presence is usually related to deer populations, but tick numbers are rising and spreading into regions where previously absent, largely due to climate change.


“Ticks are inactive in winter and only start looking for a host when the mean weekly temperature exceeds 7degC, so as the onset of spring approaches, tick infestation will become an increased risk.


“A humidity of at least 85 per cent is required for survival when ticks are off the host animal.”


Ixodes ricinus, the sheep tick, is the vector for five diseases: louping ill, tickborne fever, redwater fever, tick pyaemia and the zoonotic lyme disease.


In addition to the main diseases caused by infected ticks, the parasite itself can cause irritation, anaemia and loss of production in livestock.


Dr Rocchi says: “The surveillance unit at Moredun is currently looking at better ways to diagnose tick-transmitted diseases.


“Tick control should be planned for individual farms as part of the flock health plan, in consultation with the farm’s vet.”

louping ill

Louping ill

Louping ill is the most common sheep disease spread by ticks in the UK, but there is a vaccine available to protect stock from the disease.


It is a viral disease affecting the central nervous system and is principally found in sheep, according to Dr Reid.


He says: “Ticks become infected when they feed on a host which was previously infected with the virus from another tick.


“The virus establishes in the salivary gland of the tick and is injected into another host when the tick feeds again after moulting.


“In areas where the disease is constantly present, many animals develop mild infections with only a few progressing towards neurological signs. After this, the antibody response in the host eliminates the virus from the bloodstream and provides strong immunity for the rest of the sheep’s life.”


In some animals, mainly cattle, clinical signs can become persistent, resulting in partial paralysis and an inability to rise for several weeks.

 

Tick pyaemia

This disease is also referred to as ‘crippled lambs’, where animals develop severe lameness and paralysis of the back-end.


Abscesses form in various parts of the body and can affect up to 30 per cent of lambs in the group. Lambs with tickborne fever are more susceptible to develop tick pyaemia. To limit the disease, the tick population needs to be controlled as there is no treatment.

Why are tick populations increasing and spreading?

  • Climate change; particularly wet summers
  • Sheep farming economics and a reduction in sheep dipping
  • Changing environmental biodiversity management strategies in relation to the habitat
  • Increasing deer numbers acting as tick maintenance hosts

Tickborne fever

The bacteria anaplasma phagocytophilum causes tickborne fever in sheep and affects the immune system.


The disease is prevalent wherever ticks and sheep are present.


All ages of animal are susceptible and maternal antibodies in colostrum provide no protection. Clinical signs of the disease includes a sustained high temperature, anorexia and depression.


Dr Reid says: “Pregnant ewes exposed to infected ticks for the first time are likely to abort and may develop severe metritis [inflammation of the uterus] if untreated.”

 

Redwater fever

A protozoan parasite which lives in the red blood cells, transmitted by sheep tick, causes this cattle disease.


Dr Rocchi said: “The disease is rarely a problem as cattle under nine months old do not develop clinical disease following infection, but become solidly immune.


“A herd of cattle which are resident in a tick-infested area will rarely be susceptible to the disease, but when naive animals which have not been exposed to the disease before, or when infected ticks encroach into new areas, risk of disease increases.


“Clinical signs will usually begin two weeks after infection and include the sudden appearance of a high fever, anorexia, depression and weakness with rapid breathing, diarrhoea and blood-red urine – giving the disease its name.


“Infected pregnant animals may abort and, if left untreated, the animal will become comatose and die.”


If red water is suspected in a herd, your vet should be consulted immediately as diagnosis can be confirmed by examining blood smears under the microscope.

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