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An infectious viral disease, louping ill is mainly found in sheep. Despite this, other mammals such as red grouse, dogs, horses, deer, pigs, and cattle are also able to become infected by the causal pathogen. Death can result from the disease. Ewe lambs can die from this infection and this usually occurs in their second spring. When red grouse are affected there can be fatal consequences for the animal.

 

Infectious Ovine Encephalomyelitis

Also known as infectious ovine encephalomyelitis, louping ill is caused by the louping ill virus (LIV) which belongs to a family of viruses called Flaviviridae. Initially, the virus multiplies in the lymphatic tissue. It is an acute viral disease and the louping ill virus adversely affects the central nervous system (CNS) of the infected sheep.

 

Sheep of all ages may be infected by the disease although younger lambs with non-immune mothers are more severely affected. This is because their immune systems will not have developed as fully as those of the older sheep in the flock. The virus is generally transmitted via infected ticks biting the animal.  The signs and symptoms of louping ill include fever, tremors, uncoordinated movements and a coma. Over half of infected animals can die.

 

Vaccinations are available and ewes are often administered the vaccine during pregnancy to protect the lambs. The disease is zoonotic but this is very rare. This means that infectious ovine encephalomyelitis may be transmissible to humans. This can occur if the humans are bitten by an infected tick or come into contact with infected tissues.   

Transmission of louping ill

The main method of transmission involved in the spread of louping ill is bites from ticks which are carrying the virus. Thus, the tick acts as a vector for louping ill. Infected sheep and grouse are able to pass on the virus to ticks thus contributing to widespread nature of the disease. The main responsible tick for this is known as Ixodes ricinus which are more active in spring. The tick is particular prevalent in rough grazing areas.

Bought in sheep can be transmitted the disease when introduced to a new herd.  It has been suggested that goats can shed the virus in their milk when lactating. Infected animal tissues and instruments can pass on the disease via direct contact with an unaffected animal. Aerosol exposure may also spread the disease.

Signs and Symptoms of Infectious Ovine Encephalomyelitis

The symptoms of louping ill vary in sheep usually depending on the amount of virus that is found to be in the blood and the severity of damage caused to the central nervous system. Some sheep show no symptoms at all and so are named asymptomatic. In spite of this, the majority of sheep are affected very adversely by this viral infection.

Initially the sheep will show signs of fever, which occurs in two phases. This can result in depression in the infected animal as well as a possible increased sensitivity to sounds. Drooling may result along with a reluctance to eat. The infected animal may not be able to pass faeces, thus becoming constipated.

 

If the pathogen reaches the central nervous system then this also affects the animal such that a lack of coordination with the sheep’s own muscles is observed and the hind legs may collapse, experience torticollis or become paralysed. A louping gait or muscular tremors can be observed. The disease progresses to a prolonged state of unconsciousness and fatalities can occur usually under age of two years old. Sudden death can also be a result of infection although if the central nervous system is not affected than the animal may rapidly recover.

 

Treatment of louping ill 

As with many viral infections, there is no specific treatment used to treat louping ill disease. Antibiotic therapy is not able to destroy viruses and therefore is not used as a part of the treatment plan.

 

Supportive therapy may be given to treat the symptoms. For example, if anorexia is present then bottle or hand feeding may be necessary. Some veterinarians may be able to give the louping antiserum provided the animal was infected within a period of two days. Animals with posterior paralysis and are recumbent are often euthanized to reduce further suffering.

 

Prevention of Infectious Ovine Encephalomyelitis

Preventing infections of louping ill can prove to be economically worthwhile in comparison to costs and losses when dealing with an outbreak of the disease. Preventative measures include reducing the amount of ticks residing on the sheep as well as vaccinations.

Vaccines are available and are long lasting. In order to successfully eradicate the disease on sheep farms, sheep should be regularly vaccinated against louping ill. The vaccine is initially administered in two doses. Flock vaccination not regularly given in endemic areas can never fully eradicate the disease since wildlife is able to transfer the disease. Bought in animals should be vaccinated a month prior to introduction to an area of high incidence and vaccination of ewes provides passive immunity for a short period of time to their lambs. 

 

Complete removal of ticks is not possible since wildlife is also able to carry these parasites. However, their numbers can sometimes be reduced by culling animals infected with the disease or putting them in quarantine. Animals that are recumbent should be culled. Dipping sheep with ectoparasiticides may be an option although this can prove harmful to lambs. Spraying frequently can also reduce the numbers. In some areas, measures can be taken to decrease the amount of ticks in the environment where the sheep graze. Overall, decreases in tick numbers decreases vectors transferring the disease and thus its spread.

 

Diagnosis of louping ill

Infectious Ovine Encephalomyelitis is initially diagnosed by the clinical signs and by acquiring knowledge of the history of the flock and the area. This includes finding out whether there is a high risk of ticks in the environment. However, a definitive diagnosis is need.  This is done via isolating the virus and its antigens or nucleic acids from brain stem of the central nervous system. Blood may also be sampled to find the virus in the acute stage of infection.

 

Prognosis for louping ill

The prognosis for lambs which acquire the necessary antibodies from their mother’s colostrum is good and they can gain immunity for a few months. Fatalities can occur in as much as every one in ten sheep and sheep in endemic areas have a 60% chance of infection.

 

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