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African horse sickness vaccine shows promise in mice

African Horse Sickness is spread by Culicoides species midges.

African Horse Sickness is spread by Culicoides species midges.

Testing of a recombinant vaccine against the deadly disease, African horse sickness, has produced promising results in mice, researchers report.

Recombinant vaccines are created by usng bacteria or yeast to produce large quantities of a single viral or bacterial protein. This protein is then purified and injected into the patient, and the patient’s immune system makes antibodies to the disease agent’s protein, protecting the patient from natural disease.

Advantages of the recombinant vaccine technology are that there is virtually no chance of the host becoming ill from the agent, since it is just a single protein, not the organism itself.

Researchers from Spain and Britain reported in the peer-reviewed open-access journal, PLoS ONE, that they had engineered a recombinant modified vaccine expressing two proteins from the AHSV-4 serotype.

Javier Ortego and his colleagues reported that mice inoculated with it generated significant levels of neutralizing antibodies specific of AHSV-4.

Vaccination also stimulated specific T cell responses against the virus.

The vaccine also induced cross-protection against the heterologous AHSV-9 serotype.

The researchers described the levels of immunity as very high.

African horse sickness is caused by an Orbivirus of the family Reoviridae that causes a severe disease in equids.

In susceptible horses, the mortality could reach 90 percent.

Although cases are mostly mostly confined to sub-Saharan Africa, there are sporadic outbreaks in North Africa, Pakistan, India, Portugal and Spain.

Nine serotypes of the virus, AHSV-1 to AHSV-9, have been described.

AHSV is transmitted by Culicoides midges, the same insect vectors as those that transmit bluetongue virus, which mostly affects sheep and cattle.

Since 2008, there has been a dramatic northward spread of bluetongue virus in Europe related to the extension of the insect’s habitat due to climate change.

There are therefore fears of AHSV spreading into Europe, with potentially disastrous consequences for the naive horse population and associated industries.

Vaccination with a live-attenuated polyvalent AHSV vaccine is used to control the disease in Africa, the researchers noted.

“However, this type of vaccine causes viraemia [a condition in which virus particles circulate and reproduce in the bloodstream] in the host and therefore has the potential to be acquired by the vector and transmitted in the field.

“In addition, a recent study showed that horses immunized against AHSV can be infected both clinically and subclinically with AHSV following natural infection in field conditions.

“Indeed, the level of viraemia observed in subclinically infected horses might be sufficient to infect midges with AHSV.

“These attenuated vaccines have other disadvantages, such as the possible exchange of genome segments with field strains and the impossibility to distinguish (naturally) infected and vaccinated animals.”

The researchers were from from the Animal Health Research Center of the National Research Institute for Agriculture and Food Technology in Madrid, Spain, and the Pilbright Institute in Surrey, England.

 

de la Poza F, Calvo-Pinilla E, López-Gil E, Marín-López A, Mateos F, et al. (2013) Ns1 Is a Key Protein in the Vaccine Composition to Protect Ifnar(−/−) Mice against Infection with Multiple Serotypes of African Horse Sickness Virus. PLoS ONE 8(7): e70197. doi:10.1371/journal.pone.0070197

 

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