African horse sickness and Bluetongue at a glance

African horse sickness at a glance

Peste-equina

African horse sickness (AHS) is an infectious but non-contagious viral disease, transmitted by Culicoides, affecting all species of equidae. The disease is caused by an Orbivirus of family Reoviridae and it is characterised by alteration in the respiratory and circulatory functions.

Nine virus serotypes are known. All serotypes occur in South and Eaast Africa. Serotypes 9, 4 and 2 have been found in North and West Africa from where they occasionally spread into countries surrounding the Mediterranean. Examples of outbreaks that have occurred outside Africa are: in the Middle East (1959–1963), in Spain (serotype 9, 1966, serotype 4, 1987–1990), and in Portugal (serotype 4, 1989).

Laboratory diagnosis of AHS is essential. Although the clinical signs and lesions are characteristic, they can be confused with those of other equine diseases. As a viral disease, the laboratory diagnosis of AHS can be based on the identification of virus, virus nucleic acid, viral antigens or specific antibodies. Over the past few years, a wide variety of laboratory tests have been adapted for the detection of both AHS virus (AHSV) and specific antibodies.

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Bluetongue at a glance

cow

Bluetongue (BT) is a non-contagious, viral disease affecting domestic and wild ruminants (primarily sheep and including cattle, goats, buffalo, antelope, deer or elk) that is transmitted by midges of the Culicoides species.

Infection with bluetongue virus (BTV) is unapparent in the vast majority of animals but can cause fatal disease in a proportion of infected ruminants. The severity of disease varies among different species and strains with symptoms being most severe in sheep resulting in deaths, weight loss and disruption in wool growth. In highly susceptible sheep, morbidity can be as high as 100%. Mortality averages from 2-30% but can be as high as 70%. It is not known to affect humans.

The virus which causes BT is identified as a member of Orbivirus genus of the family Reoviridae. The BT virus species, or serogroup, contains at least 26 recognised serotypes, although only serotypes 1 to 24 are currently notifiable disease.

The BT virus has been shown to be present in regions where the Culicoides is present (e.g. Africa, the Americas, Australia, the Middle East and some countries of southern Asia). BT situation in the EU has considerably changed in recent times. Since 1998 BTV has been present in Southern European and Mediterranean countries from which it has gradually spread to areas previously free of the virus. In Northern Europe BT virus serotype 8 epidemics broke out suddenly and unexpectedly in August 2006.

Vaccination can prevent clinical BT or at least mitigate its course by interrupting the BT virus cycle in the environment; it thus re¬duces the economic losses due to animal infection and makes transfer and trading of animals from BTV enzootic regions possible. Bluetongue vaccines are serotype-specific and therefore, before use in a given area, the serotypes present in the environment should be taken into account. Two types of vaccines, inactivated and live attenuated, are currently available.

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