Parasite Tolerance and Host Competence in Avian Host Defense to West Nile Virus

Abstract

Competence, or the propensity of a host to transmit parasites, is partly underlain by host strategies to cope with infection (e.g., resistance and tolerance). Resistance represents the ability of hosts to prevent or clear infections, whereas tolerance captures the ability of individuals to cope with a given parasite burden. Here, we investigated (1) whether one easy-to-measure form of tolerance described well the dynamic relationships between host health and parasite burden, and (2) whether individual resistance and tolerance to West Nile virus (WNV) were predictable from single cytokine measures. We exposed house sparrows (HOSP) to WNV and measured subsequent changes in host performance, viral burden, and cytokine expression. We then used two novel approaches (one complex, one simpler) to estimate tolerance within-individual HOSP using four separate host performance traits. We lastly investigated changes in the expression of pro-inflammatory cytokine interferon-γ (IFN-γ) and anti-inflammatory cytokine interleukin-10 (IL-10). Both approaches to estimating tolerance were equivalent among WNV-infected HOSP; thus, an easy-to-measure tolerance estimation may be successfully applied in field studies. Constitutive expression of IFN-γ and IL-10 were predictive of resistance and tolerance to WNV, implicating these cytokines as viable biomarkers of host competence to WNV.

Climate Change Could Increase the Geographic Extent of Hendra Virus Spillover Risk

“…Although the final models are complex due to a lack of understanding of the interaction of flying foxes and horses, the statistical associations in the models of the P. alecto system are similar with those found in Martin et al ( 2018 ). First, most of the variables’ interactions that were kept in the model represent rainfall ( bio12 ) and its seasonality ( bio15 ).…”

“…2 ) and relative lack of disease surveillance. While the effect of horse density on risk of spillover seems negligible (McFarlane et al 2011 ) or negative depending on the spatial scale (Martin et al 2018 ), the presence of horses is conditional for spillover (Plowright et al 2015 ).…”

“…In fact, high suitability for P. alecto is not enough to explain spillover because Maxent.p.alecto alone had a negative effect which is reversed when it interacts with rainfall levels (Table 1 ). We can infer from these associations that rainfall levels and their variability with respect to seasonal extremes could be broad-scale correlates of HeV spillover risk (Páez et al 2017 ; Martin et al 2018 ).…”

“…HeV spills over to horses from two of the four Australian flying fox species (Smith et al 2014 ; Edson et al 2015 ; Martin et al 2016 ). We treated these species as two separate reservoir host systems (Smith et al 2014 ; Edson et al 2015 ; Martin et al 2018 ) that were geographically limited to the areas colonisable by P. alecto and P. conspicillatus (Soberón et al 2005 ; Martin et al 2016 ). The colonisable areas comprise the climatic regions of Australia (obtained from the bureau of meteorology, http: www.bom.gov.au ) that contain at least one presence record of each reservoir host.…”

Macroimmunology: The drivers and consequences of spatial patterns in wildlife immune defence

“…For example, a captive study of house sparrows exposed to West Nile virus assessed whether resistance or tolerance could be predicted with cytokines. Higher constitutive expression of a pro‐inflammatory cytokine predicted shorter infectious periods (indicating stronger resistance), whereas greater expression of an anti‐inflammatory cytokine was associated with improved tolerance (Burgan, Gervasi, & Martin, ). Validation of biomarkers for such traits would improve inference in macroimmunology.…”