Bluetongue Disease: a viral disease

Ankita Chattopadhyay, Amity University Kolkata

Bluetongue is a viral disease affecting sheep, cattle, deer, and goats. It is a non-contagious, insect-borne disease to which all species of ruminants are susceptible. Studies show that sheep are mostly the victims but the cattle are the main mammal reservoir of the virus. This virus is a notifiable disease in many countries and is caused by a virus belonging to the group Reoviridae. 

The Bluetongue virus has been confined to tropical and subtropical areas. However, endemic areas now exist in Africa, Europe, the Middle East, North, and South America and Asia as well as on islands such as Australia, the South Pacific, and the Caribbean. The occurrence of an outbreak can take place way behind permitted areas, but the BTV virus does not persist once cold weather kills the Culicoides vectors. 

Symptoms-

The symptoms consist of fever, widespread haemorrhages of oral and nasal tissue, excessive salivation, and nasal discharge. In a few cases, the lips and tongue swell, and this swelling might extend below the lower jaw. The reduced feed consumption due to the painfully inflamed mouths might be symptoms of this disease due to swelling of the cuticle. Convalescence of surviving sheep is slow. The high fever in sheep leads to wool loss, which gives rise to production losses. Some like goats, cattle, wild ruminants such as deer can appear healthy when infected. This may lead to silent spread by midges feeding on the infected animals.

Spread-

The virus cannot be transmitted without the presence of insect carriers and between susceptible animals. The geographical distribution of bluetongue depends on seasonal conditions, the availability of the susceptible species of animals, and the presence of insect vectors. The ones that are in greatest numbers are insect carriers, biting midges that prefer warm, moist conditions and most are prominent after rains.

The Responsible Virus- 

The Bluetongue virus is not outside the insect vector and for sure animal products like meat and wool aren’t the medium. The survival of a virus within a particular area is dependent on whether it can overwinter in that area. With the potential for still more to be developed, almost 26 different species of Bluetongue virus has been developed. The Bluetongue genome evolves rapidly via mutations. Some of the virus variants may be selected for they can adapt to the environmental conditions. The main mechanism that leads to the genetic diversity amongst the field strains is the evolution and selection of variations during the transmission of BTV between susceptible animals and vectors. 

Diagnostics-

After BTV being suspected, the first step is to contact a veterinarian. The next step is the collection of blood samples by the vet for diagnostic testing to confirm whether animals are infected with BTV. As there are 26 different types of BTV, it is very important to have a single test that can detect the presence of these viruses. The next step is to serotype the strain to apply the appropriate vaccine. The quick and reliable tool to identify the existence of the BTV virus is the Real-time polymerase chain (rt-PCR) detection tool. Diagnostic test tools’ capabilities are regularly tested to detect new variants. Virus diversity needs to be closely monitored. 

Also read: Efficient and cost-effective Bacterial mRNA sequencing causing ribosomal RNA depletion

References-

• G Ferrari, C De Liberato, G Scavia, et al.; Active circulation of bluetongue vaccine virus serotype-2 among unvaccinated cattle in central Italy; 2005; Preventive Veterinary Medicine; Vol: 68, Issues 2–4, Pages 103-113; DOI: 10.1016/j.prevetmed.2004.11.011

• Andrea S. Lear and Robert J. Callan; Overview of Blutongue; 2014; MSD MANUAL Veterinary Manual; URL – https://www.msdvetmanual.com/generalized-conditions/bluetongue/overview-of-bluetongue
• Simon Carpenter, Anthony Wilson and Philip S Mellor; Culicoides and the emergence of bluetongue virus in northern Europe; 2009;  Trends in Microbiology, DOI -10.1016/j.tim.2009.01.001

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