Discussion on a Selection of Key Scientific Articles

By John Atkinson, Associate Director Intergovernmental Veterinary Health

 

Schmallenberg disease in UK flocks
Veterinary Record, 180 ( 4 ) p100. Lewis, C., 2017

Key Thoughts:
Vector-borne diseases are an important threat to livestock health and production globally. As emphasis within the veterinary sphere is moving towards preventing disease rather than relying on treatments, it is important to consider our attitude towards the role of vaccination. For many diseases, vaccination should be carried out before disease outbreaks occur. This is relatively straightforward to justify when it comes to many endemic diseases, but what about those diseases appearing over a longer timeframe? Given their predictability, regular vaccination against diseases which re-emerge every few years should be considered, and collaboration involving all key stakeholders is vital if this is to be achieved.

Article Summary:
Schmallenberg disease causes deformities in lambs, as well as calves and goats, following infection of the foetus during pregnancy. After a three-year absence, Schmallenberg disease has reappeared in the UK after being confirmed in sheep in southern England. The re-emergence of the disease is not surprising given how closely related it is to the Akabane virus, which causes disease outbreaks elsewhere in the world every 3-6 years.

Immunity is strong in non-pregnant animals and those pregnant out-with the window for infection, with clinical disease being seen when younger, naïve animals enter the breeding flock or move into an infected area. The virus is suggested as being maintained in vectors, wildlife or non-pregnant animals during the years between outbreaks. Given the high likelihood of outbreaks every few years in the future, regular vaccination may become important despite vaccine uptake being poor in the past.

Lumpy skin disease outbreaks in Greece during 2015-16, implementation of emergency immunization and genetic differentiation between field isolates and vaccine virus strains
Veterinary Microbiology, 201 pp 78-84. Agianniotaki, E. I. et al, 2017

Key Thoughts:
As the ranges of vector-borne diseases like lumpy skin disease (LSD) increase it is essential that veterinary services within countries are ready to deal with the emerging threat they pose. Accurate recognition of clinical signs and laboratory diagnosis are essential, with the development of new diagnostic methods helping achieve this. The sharing of experiences about LSD outbreaks and their control is of great benefit in helping countries prevent and control this serious disease in the most effective way.

Article Summary:
Lumpy skin disease (LSD) is an economically important disease that is caused by a type of Capripox virus (CaPV). It has been spreading north and eastwards out of Africa into the Middle East and Turkey since 2012. By 2015, it reached Europe, having first been recorded in Greece in August, prompting emergency vaccination of cattle and buffalo with vaccines containing a Neethling-like strain together with stamping-out, movement restrictions and vector control. High vaccination coverage was important to prevent further outbreaks, and the analysis of the data from the 2015/16 outbreak supports timely and intensive vaccination in order to control LSD.

During the 2015/16 Greek outbreak, state veterinarians were central in evaluating and sampling suspected LSD cases and applying vaccinations. The National Reference Laboratory for CaPVs isolated and sequenced the field LSD virus from nodular tissue of clinically affected, unvaccinated animals. Sequencing of the vaccinal strains from the two live attenuated vaccines was also undertaken. There were significant differences between the field and vaccinal strains, which enabled the development of a PCR analysis method that does not require significant equipment to discriminate between the field and vaccinal strains of the LSD virus.

A small proportion of vaccinated animals were found to show mild, transient nodular skin lesions post-vaccination. The PCR method described has the potential to prevent such animals from being culled unnecessarily because it could help demonstrate that they have been vaccinated and are therefore protected. This is a useful development given that vaccination is the most effective way of controlling outbreaks.

 

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