Bluetongue disease is an infectious process, but not contagious among animals because they need a mosquito for transmission. Animals susceptible to infection by bluetongue virus are ruminants, but only sheep will show clinical signs of the disease. Humans cannot be affected, it is not a zoonosis. Cows are the best reservoirs of the virus due to their long viremia. In the pathogenesis of the disease, the virus causes its damage to the endothelium of blood vessels. The diagnosis is laboratory and there is no treatment as it is a notifiable disease on list A of the World Organization for Animal He alth.
Keep reading this article on our site to learn all about bluetongue disease, its symptoms and treatment.
What is bluetongue in animals?
Bluetongue is an infectious disease, but not contagious, which affects wild and domestic ruminant animals, but which causes symptoms clinical only in sheep.
Although bluetongue may be present in cows or goats, they generally do not show clinical signs, however, cows are often the mosquito's preferred reservoir of the virus. In addition, the virus in the blood can remain for a month to a month and a half so that they are infective for the mosquitoes that transmit it, unlike sheep and goats in which high viremia (virus in blood) does not last more than 15 days. Therefore, bluetongue in cattle and goats is not important symptomatologically, but it is in the epidemiology of the disease as they are considered viral reservoirs for the mosquito, especially cattle. Discover in this other article the most common diseases of cattle.
In sheep the disease can become very serious, with average mortality of 2% to 30%, although it can reach 70%.
Bluetongue is a disease listed in the OIE Terrestrial Animal He alth Code and must always be notified to the World Organization for Animal He alth (OIE). It is a disease that is of great economic importance in endemic regions because it produces direct economic losses due to decreased production and deaths, and indirect ones due to the price of preventive measures and restrictions on animal trade.
Is bluetongue transmitted to humans?
No, is not a zoonosis, it is a disease that only affects ruminants with or without symptoms. In addition, it is not directly transmissible between them, since they require a transmitting vector, in this case a mosquito.
What virus causes bluetongue disease?
Bluetongue is a disease caused by the bluetongue virus, an RNA virus belonging to the family Reoviridae and the genus Orbivirus, transmitted by vectors. Specifically, they are mosquitoes of the genus Cullicoides:
- Culicoides imicola
- Culicoides obsoletus
- Culicoides pulicaris
- Culicoides dewulfi
These mosquitoes have crepuscular and nocturnal activity and are found in areas with warm temperatures, high humidity in the environment and no air. Hence, transmission of the virus occurs especially in periods of rain and warm temperatures (late spring or early fall).
Due to the need for exclusive transmission by a vector mosquito, the disease areas coincide with the vector regions, specifically Europe, North America, Africa, Asia, Australia and various islands in the tropics and subtropics.
In addition to contagion by the females of these mosquitoes due to their hematophagous habits, transplacental transmission and semen transmission have been seen.
The virus has more than 27 serotypes, but they are independent and there are no cross-reactions, and specific vaccination for the serotype in question is mandatory for each outbreak.
Symptoms of bluetongue in animals
The virus replicates early in the infection in vascular epithelium and regional lymph nodes. From there, it spreads through the blood to other lymph nodes and lungs protected by invaginations in red blood cells. The virus primarily causes damage to the endothelium of blood vessels, which can cause edema, vasculitis, hemorrhage, microthrombi and necrosis.
Bluetongue virus can also multiply in stimulated macrophages and lymphocytes. The lesions are more evident in the oral cavity, around the mouth and on the hooves. Specifically, the symptomatology of a sheep with bluetongue virus may include:
- Fever 5-7 days after infection.
- Serous to hemorrhagic nasal discharge.
- Serous to hemorrhagic ocular discharge.
- Swelling of the lips, tongue and jaw.
- Psialorrhea (hypersalivation).
- Depression.
- Anorexy.
- Weakness.
- Limp.
- Wool fall.
- Respiratory difficulty.
- Profuse diarrhoea.
- Vomiting.
- Pneumonia.
- Abortions.
- Hyperemia in the coronary band of the hooves.
- Face and neck edema.
- Hemorrhages and erosions in the oral and nasal cavities.
- Pulmonary artery hemorrhage.
- Hemorrhages in the skin and connective tissue.
- Muscle necrosis.
- Lung edema.
- Swelling and cyanosis of the tongue (blue tongue).
Remember that the bluetongue virus in cows and goats does not produce clinical signs, which is why we focus on symptoms in sheep.
Diagnosis of bluetongue disease
Faced with these symptoms in sheep, the following diseases should be considered:
- Bluetongue.
- Pedero.
- Contagious ecthyma.
- Aphtose fever.
- Peste des petits ruminants.
- Rift Valley Fever.
- Sheeppox.
In addition to the clinical signs that the sheep develops, it is necessary to confirm the diagnosis by taking samples and sending them to the laboratory for carrying out direct or indirect tests for the detection of the virus. The direct tests that detect the virus in blood and serum with EDTA, tongue, nasal mucosa, spleen, lung, lymph nodes or heart are:
- Antigen capture ELISA.
- Direct immunofluorescence.
- RT-PCR.
- Seroneutralization.
The indirect tests to look for antibodies to the virus in serum from unvaccinated sheep are:
- Competition Elisa.
- Indirect ELISA.
- Agar gel immunodiffusion.
- Seroneutralization.
- Complement Fixation.
Control of bluetongue in animals
There is no treatment for bluetongue Because it is an OIE list A notifiable disease and so devastating for sheep, unfortunately the treatment is prohibited. What the regulation establishes that must be done is to sacrifice the infected animals and destroy the bodies.
Since animals cannot be treated once infected, control of this disease is based on preventive measures to avoid the virus and infection when an outbreak is suspected or appears, consisting of:
- Establishment of a protection zone and a surveillance zone.
- Prohibition of movement of ruminants within the protection zone.
- Use of insecticides and mosquito repellents.
- Entomological and serological controls in ruminants.
- Vaccination of sheep with the specific serotype of the outbreak.
- Control of animal transport and disinsection of vehicles used.
- Declaration to the authorities of all new cases that may appear.
Carrying out correct prevention of bluetongue disease is vital to save the lives of these animals.
