Host Genetic Diversity and Infectious Diseases. Focus on Wild Boar, Red Deer and Tuberculosis

Abstract

Host genetic diversity tends to limit disease spread in nature and buffers populations against epidemics. Genetic diversity in wildlife is expected to receive increasing attention in contexts related to disease transmission and human health. Ungulates such as wild boar (Sus scrofa) and red deer (Cervus elaphus) are important zoonotic hosts that can be precursors to disease emergence and spread in humans. Tuberculosis is a zoonotic disease with relevant consequences and can present high prevalence in wild boar and red deer populations. Here, we review studies on the genetic diversity of ungulates and determine to what extent these studies consider its importance on the spread of disease. This assessment also focused on wild boar, red deer, and tuberculosis. We found a disconnection between studies treating genetic diversity and those dealing with infectious diseases. Contrarily, genetic diversity studies in ungulates are mainly concerned with conservation. Despite the existing disconnection between studies on genetic diversity and studies on disease emergence and spread, the knowledge gathered in each discipline can be applied to the other. The bidirectional applications are illustrated in wild boar and red deer populations from Spain, where TB is an important threat for wildlife, livestock, and humans.

Keywords: Cervus elaphus; Sus scrofa; disease spread; genetic diversity; red deer; tuberculosis; wild boar.

Figure 1

Number of published studies on genetic diversity for the most frequently studied ungulates. Results from a search on the Web of Science with the following search terms: genetic diversity, inbreeding, and ungulates (217 studies were obtained). Studies on genetic diversity of ungulate populations published in scientific journals were selected (204 papers). Total: number of studies on genetic diversity of ungulate populations published in scientific journals. Conservation: number of studies that explicitly related genetic diversity to conservation (papers in which the word ‘conservation’ appeared in the title, abstract, or the name of the journal). Diseases: number of studies that explicitly associated genetic diversity with diseases (papers in which the title, abstract, or name of the journal used at least one of the following terms: ‘disease’, ‘pathogen’, ‘parasite’, any variation of ‘immunity’, or the name of any disease). Bb: Bison bonasus, Bt: Bos taurus, Ce: Cervus elaphus, Cn: Cervus nippon, Ec: Equus caballus, Ol: Oryx leucoryx, Oa: Ovis aries, Oc: Ovis canadensis, Ss: Sus scrofa. The search was last consulted on 15 April 2021. See Tables S1 and S2.

Figure 2

Studies on tuberculosis in wild boar and red deer populations from 1990 to April 2021. Results from the search on the Web of Science described in Table 1 (Selected papers). Colored points indicate the year in which studies explicitly relating tuberculosis to reservoir genetic diversity were published. Red points: studies for wild boar. Blue points: studies for red deer. See Tables S3 and S4.

Figure 3

Mean and 95% confidence intervals for observed and expected heterozygosity of fetuses in wild boar and red deer females that produced daughters. Expected heterozygosity was obtained after simulating random mating for each species. See description of the analysis in Table 2.