RESUMO
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.
RESUMO
Citrus tristeza virus (CTV) causes severe losses in grapefruit production in South Africa and requires mild-strain cross-protection to maintain production. Unfortunately, cross-protection breakdown of the pre-immunizing CTV grapefruit mild source GFMS12 is prevalent in grapefruit in South Africa. The CTV genotype composition of the GFMS12 population inoculated onto different hosts was determined by sequencing part of ORF1a and the p23 gene of multiple clones from each plant. Analysis of the GFMS12 population in Mexican lime and Marsh and Star Ruby grapefruit varieties revealed that at least four genotypes occur in the GFMS12 population and that genotype compositions differed amongst the populations in different host plants. Single-aphid-transmitted sub-isolates derived from the GFMS12 mother population on Mexican lime appeared to contain three populations of a mixture of VT-like and recombinant B165/VT-like genotypes; a mixture of recombinant RB/VT- and B165/VT-like genotypes; and a single recombinant B165/VT-like genotype. This study underlines the importance of determining the genotype composition of a potential CTV pre-immunizing source on a range of inoculated host species before utilization.
