Abstract
Detecting exposure to new or emerging pathogens is a critical challenge to protecting human, domestic animal, and wildlife health. Yet, current techniques to detect infections typically target known pathogens of humans or economically important animals. In the face of the current surge in infectious disease emergence, non-specific disease surveillance tools are urgently needed. Tracking common host immune responses indicative of recent infection may have potential as a non-specific diagnostic approach for disease surveillance. The challenge to immunologists is to identify the most promising markers, which ideally should be highly conserved across pathogens and host species, become upregulated rapidly and consistently in response to pathogen invasion, and remain elevated beyond clearance of infection. This study combined an infection experiment and a longitudinal observational study to evaluate the utility of non-specific markers of inflammation [NSMI; two acute phase proteins (haptoglobin and serum amyloid A), two pro-inflammatory cytokines (IFNγ and TNF-α)] as indicators of pathogen exposure in a wild mammalian species, African buffalo (Syncerus caffer). Specifically, in the experimental study, we asked (1) How quickly do buffalo mount NSMI responses upon challenge with an endemic pathogen, foot-and-mouth disease virus; (2) for how long do NSMI remain elevated after viral clearance and; (3) how pronounced is the difference between peak NSMI concentration and baseline NSMI concentration? In the longitudinal study, we asked (4) Are elevated NSMI associated with recent exposure to a suite of bacterial and viral respiratory pathogens in a wild population? Among the four NSMI that we tested, haptoglobin showed the strongest potential as a surveillance marker in African buffalo: concentrations quickly and consistently reached high levels in response to experimental infection, remaining elevated for almost a month. Moreover, elevated haptoglobin was indicative of recent exposure to two respiratory pathogens assessed in the longitudinal study. We hope this work motivates studies investigating suites of NSMI as indicators for pathogen exposure in a broader range of both pathogen and host species, potentially transforming how we track disease burden in natural populations.
Highlights
Emerging infectious diseases cause human suffering [1, 2], threaten food security [3], and contribute to the decline of vulnerable populations and species [4]
In the experimental study we asked [1] How quickly do buffalo mount NSMI responses upon challenge with an endemic pathogen, footand-mouth disease virus (FMDV); [2] for how long do NSMI remain elevated after viral clearance; and [3] how pronounced is the difference between peak NSMI concentration and baseline NSMI concentration? In the longitudinal study, we asked [4] Are elevated NSMI associated with recent exposure to seven bacterial and viral respiratory pathogens, in a natural host population?
African buffalo (Syncerus caffer) included for this study were located within Kruger National Park (KNP), a 19,000 km2 reserve located in northeastern South Africa
Summary
Emerging infectious diseases cause human suffering [1, 2], threaten food security [3], and contribute to the decline of vulnerable populations and species [4]. In the face of elevated rates of infectious disease emergence in humans [5, 6], domestic animals [7] and wildlife [8,9,10], effective surveillance for pathogen exposure is increasingly important. Surveillance for emerging infections is challenging because it requires detection of previously unreported infectious agents, and/or diagnosis of exposure or infection in understudied animal species. Available disease diagnostics typically target known infections that cause detectable pathology in humans or economically important domestic animals resulting in a relatively narrow range of tests that are highly pathogen specific. Antibody-based techniques typically used in disease diagnostics are highly pathogen specific, which limits their utility in detecting novel infections
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