African horse sickness in naturally infected, immunised horses

Abstract

SummaryTo determine whether subclinical cases, together with clinical cases, of African horse sickness (AHS) occur in immunised horses in field conditions, whole blood samples were collected and rectal temperatures recorded weekly from 50 Nooitgedacht ponies resident in open camps at the Faculty of Veterinary Science, University of Pretoria, Onderstepoort, during 2008-2010. The samples were tested for the presence of African horse sickness virus (AHSV) RNA by a recently developed real-time RT-PCR. It was shown that 16% of immunised horses in an AHS endemic area were infected with AHSV over a 2 year period, with half of these (8%) being subclinically infected. The potential impact of such cases on the epidemiology of AHS warrants further investigation.

African Horse Sickness Caused by Genome Reassortment and Reversion to Virulence of Live, Attenuated Vaccine Viruses, South Africa, 2004–2014

“…Similarly, changes in the AHS case definition that only came into effect in 2008 (after the 2004 Stellenbosch outbreak) probably resulted in an underestimation of subclinical AHSV infections during that outbreak. Whereas during the Stellenbosch 2004 outbreak only clinically affected, deceased horses were classified as having confirmed cases ( 13 ), major advances in AHS diagnostic testing (e.g., rRT-PCR–based methods) have occurred during the past 10 years that likely substantially increased the detection of subclinical infections by the time of the 2014 outbreaks ( 15 , 32 ). …”

Where are the horses? With the sheep or cows? Uncertain host location, vector-feeding preferences and the risk of African horse sickness transmission in Great Britain

“…However, the simultaneous administration of multiple vaccine strains can result in interference during vaccine virus replication, possibly resulting in incomplete immunity [51,52]. For example, a recent study has shown that immunized horses in an AHS endemic area were infected with AHSV over a 2 year period [53]. Our results suggest that incomplete immunity with a reduction in the mortality rate of the horses might lead to an increase in the basic reproduction number (figure 7).…”

Ns1 Is a Key Protein in the Vaccine Composition to Protect Ifnar(−/−) Mice against Infection with Multiple Serotypes of African Horse Sickness Virus

“…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 [10]. 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 (‘DIVA’),…”