Determining Seroconversion to Peste Des Petits Ruminants Virus

2023-10-12 Hits(275)

Peste des petits ruminants (PPR) is an infectious viral disease, primarily of small ruminants such as sheep and goats, but is also known to infect a wide range of wild and domestic Artiodactyls including African buffalo, gazelle, saiga and camels. The livestock-wildlife interface, where free-ranging animals can interact with captive flocks, is the subject of scrutiny as its role in the maintenance and spread of PPR virus (PPRV) is poorly understood. As seroconversion to PPRV indicates previous infection and/or vaccination, the availability of validated serological tools for use in both typical (sheep and goat) and atypical species is essential to support future disease surveillance and control strategies. The virus neutralisation test (VNT) and enzyme-linked immunosorbent assay (ELISA) have been validated using sera from typical host species. Still, the performance of these assays in detecting antibodies from atypical species remains unclear. We examined a large panel of sera (n = 793) from a range of species from multiple countries (sourced 2015–2022) using three tests: VNT, ID VET N-ELISA and AU-PANVAC H-ELISA. A sub-panel (n = 30) was also distributed to two laboratories and tested using the luciferase immunoprecipitation system (LIPS) and a pseudotyped virus neutralisation assay (PVNA). We demonstrate a 75.0–88.0% agreement of positive results for detecting PPRV antibodies in sera from typical species between the VNT and commercial ELISAs, however this decreased to 44.4–62.3% in sera from atypical species, with an inter-species variation. The LIPS and PVNA strongly correlate with the VNT and ELISAs for typical species but vary when testing sera from atypical species.

Peste des petits ruminants (PPR), also known as ovine rinderpest, is a contagious transboundary animal disease that primarily affects small ruminants such as goats and sheep, considered typical hosts, and is widespread across Africa, the Middle East and Asia. PPR is estimated to cause up to $2.1 billion a year in losses globally with the majority of this sum shouldered by small-scale rural farmers. The causative Morbillivirus, peste des petits ruminants virus (PPRV) of the Paramyxoviridae family, is a negative sense, single-stranded RNA virus with a genome ~ 16 kb in length, categorized into genetic lineages I–IV. The haemagglutinin, fusion and nucleocapsid proteins, encoded by the H, F and N genes respectively, are the main antigenic components of the virion. These elicit a strong cell-mediated and humoral immune response during PPRV infection, with antibodies to H and F being protective and those to N being non-protective4,5. These antibodies form the primary targets for serological assays to detect seroconversion to PPRV.

With host morbidity and mortality rates as high as 80% in naïve populations, PPR presents a considerable risk to food security, agricultural practices, biodiversity and the livelihoods of those living in affected areas. In addition to sheep and goats, the disease has also been reported in some captive and free-ranging wild and domestic Artiodactyls such as African buffalo (Syncerus caffer), camel (Camelus sp.) and antelope species such as impala (Aepyceros melampus). Bovids, camelids and Suidae species were generally considered to be dead-end hosts, playing little or no part in transmission, but recent studies have shown that these atypical hosts may develop clinical symptoms, spread disease and seroconvert in captive and experimental settings, impacting their epidemiological significance. The disease presentation and seroconversion rates in these species are therefore still being investigated. A notable natural outbreak of PPR occurred between 2016 and 2017 when wild saiga antelope (Saiga tatarica mongolica) populations in Mongolia were severely impacted, with livestock animals highlighted as the likely source of PPRV transmission.

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