Middelburg Virus in Horses

Middelburg Virus was first isolated in 1957 in a species of mosquito (Ochlerotatus caballus) in the town of Middelburg (Capetown, South Afrika). Later the Middelburg Virus was also recovered from other species of mosquito (Aedes leneatopennis and Aedes albothorax). Since then, infections with the Middelburg Virus have been observed in most of southern African countries.

Research indicates that Middelburg Virus appears to be a member of the Semliki Forest clade of the Alphaviruses and thus it has some well-knowns family members such as Chikungunya virus, O’Nyong Nyong virus and Ross River virus. Additionally, analysis indicates that the Southern Elephant Seal Virus is also part of the Semliki Forest clade[1].
Middelburg Virus can infect humans, sheep, cattle, goats and horses. There's no human disease associated with the virus, but the virus may be quite deadly for horses: the isolation of this virus in 1993 from a horse that died showing severe clinical signs represents the first indication that Middelburg Virus can cause severe disease in equids[2].

The clinical signs in horses are fever, ataxia, progressive weakness in thoriacic and pelvic limbs, recumbency, muscle fasciculation and seizures.

To date, no effective treatment has been developed for this disease in horses.

Can the disease ever reach western Europe? Yes, it easily can because several other related viruses, such as West Nile Virus, have even travelled across the Atlantic Ocean and now create havoc in the Americas.

[1] Luers et al: A phylogenomic study of the genus Alphavirus employing whole genome comparison in Comparative and Functional Genomics - 2005
[2] Attoui et al: Complete nucleotide sequence of Middelburg virus, isolated from the spleen of a horse with severe clinical disease in Zimbabwe in Journal of General Virology – 2007. See here.