Viral dynamics and immune responses to foot-and-mouth disease virus in African buffalo (Syncerus caffer)

Abstract

Foot-and-mouth disease (FMD) is one of the most important livestock diseases restricting international trade. While it is clear that African buffalo (Syncerus caffer) act as the main wildlife reservoir, viral and immune response dynamics during FMD virus acute infection have not been described before in this species. We used experimental needle inoculation and contact infections with three Southern African Territories serotypes to assess clinical, virological and immunological dynamics for thirty days post infection. Clinical FMD in the needle inoculated buffaloes was mild and characterised by pyrexia. Despite the absence of generalised vesicles, all contact animals were readily infected with their respective serotypes within the first 2-9 days after being mixed with needle challenged buffaloes. Irrespective of the route of infection or serotype there were positive associations between the viral loads in blood and the induction of host innate pro-inflammatory cytokines and acute phase proteins. Viral loads in blood and tonsils were tightly correlated during the acute phase of the infection, however, viraemia significantly declined after a peak at 4 days post infection (dpi), which correlated with the presence of detectable neutralising antibodies. In contrast, infectious virus was isolated in the tonsils until the last sampling point (30 dpi) in most animals. The pattern of virus detection in serum and tonsil swabs was similar for all three serotypes in the direct challenged and contact challenged animals.We have demonstrated for the first time, that African buffalo are indeed systemically affected by FMD virus and clinical FMD in buffalo is characterized by a transient pyrexia. Despite the lack of FMD lesions, infection of African buffalo was characterised by high viral loads in blood and oropharynx, rapid and strong host innate and adaptive immune responses and high transmissibility.

Within-host viral growth and immune response rates predict FMDV transmission dynamics for African Buffalo

“…As an additional reality check for our models, we compared model output against data on fevers mounted by the animals. The model-inferred time course of immune and viral dynamics was reasonable in the context of clinical signs [see [23] for details of the temperature data and the shaded boxes in Fig. 2 for visual representation of these inferred fever quantities].…”

“…For each strain, four buffalo were needle infected and allowed to contact four naive buffalo. These naive buffalo were then captured on contact days 0, 2, 4, 6, 9, and 12 during the acute phase and again at 28 days post infection for measurement of viral and immune parameters [see [19,23]]. The impact of route of infection on model parameters is discussed extensively in the supplementary information.…”

“…FMD is the most important trade-restricting livestock disease globally, and as a result, well-established methods exist for virus culture, experimental challenges, diagnostics, and quantifying immune responses [17,[19][20][21][22]. Previous work has shown that FMDV strains vary substantially in their transmission dynamics among buffalo hosts [19]; and viral proliferation and immune response patterns in buffalo have been described [23]. However, the functional interplay of within-host viral and immune dynamics has not been evaluated in buffalo, compared among Southern African Territories (SAT) serotypes, or aligned with population-level disease dynamics.…”