What is the blue tongue disease that affects the Balearic Islands?

Bluetongue is not infectious to humans, but it has a great impact on livestock

The Balearic Islands have started an urgent vaccination campaign in sheep and cattle

At the beginning of July, the Department of Agriculture, Fisheries and Food of the Balearic Islands confirmed the existence of an outbreak of bluetongue disease on the island of Mallorca. The samples that have tested positive come from a bovine specimen that was intended for meat consumption and that came from a cattle farm in Pollença.

Bluetongue disease is an infectious disease of viral origin caused by the bluetongue virus (vLA), which is transmitted mainly by bites of mosquitoes of the genus Culicoides. The virus has the ability to affect different species of ruminants, both domestic and wild, among which cows, goats, antelopes, camelids and cervids stand out, although especially affects sheep which are highly susceptible, being able to reach morbidity up to 100%. Average mortality is between 2% and 30% but can reach 70%.

It is not contagious to humans, but it has a high economic cost

Fortunately, a priori the disease it is not contagious to humans and there is no risk of infection from the consumption of meat or milk from positive animals. Despite this, bluetongue disease is considered a reemergence worldwide due to the great economic impact it causes.

Bluetongue outbreaks can cause losses of millions of euros Due to the impact on the health of livestock and the loss of markets, there are strict restrictions on the movement of animals to limit the spread of the disease. The impact on the livestock economy of the affected regions is very severe.

Catastrophic impact on sheep

For sheep populations, losses can be catastrophic because in susceptible herds the mortality can even reach 100%, to which must be added other losses caused by morbidity and the need to provide medical attention to sick animals. Economic losses associated with morbidity include weight loss, reduced milk and wool production, abortions, and related veterinary expenses.

It is estimated that the outbreak of bluetongue that emerged in France in 2007 was an approximate cost of 1,200 million euros, mainly as a consequence of the instability of French cattle in international markets. In the United States of America, the usual losses caused by the disease are around 130 million euros each year.

African origin

The blue tongue was described by first time in South Africa in 1902 and for a long time it was thought that it was restricted to the African continent, but in 1943 it was referred to Cyprus and from that moment the virus spread throughout the Mediterranean and other regions and continents such as the United States of America and Australia.

Climate change may have enhanced the adaptive capacity of mosquitoes vectors to European climatic conditions, facilitating the spread of the virus in northern Europe. The disease is named for its most prominent feature, which is that the affected animal’s tongue turns blue, a condition called cyanosis of the tongue.

Symptoms of infection

The virus also causes high fever, excessive salivation, swelling of the head and neck and the development of erosions and ulcerations and hyperemic-hemorrhagic lesions in the musculature, the hooves or the oral mucosa that usually compromise the life of the animal. It can also produce abortions and fetal malformations in pregnant females.

In cattle the infection rate is often higher that in sheep and the presence and severity of clinical signs vary according to the viral strain. To date, 24 serotypes have been described, but it is considered that there may be more than 30 possible.

Urgent vaccination campaign

The Balearic Ministry has confirmed the presence of the bluetongue serotype 4 on the island of Mallorca and has also stated that it is pertinent to establish the emergency for the rest of the islands of the archipelago. For this reason, the protocol for the use of vaccines has been started, since vaccination is mandatory against serotype 4 for all sheep and cattle older than three months.

Insect control is also important to limit the spread of the disease and disinfection with sodium hypochlorite or sodium hydroxide 3% is effective. Although the virus does not infect equines, horses and stables should be considered in any control scheme, as Culicoides feed on horse blood and manure accumulation sites are ideal for reproduction of these vectors.

A few months ago, in November 2020, an outbreak of the bluetongue disease detected in the Pyrenean municipality of Broto, and which came from France, forced to vaccinate more than 150,000 animals of farms located within a radius of 50 kilometers, which shows the concern caused by the appearance of this disease.

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