The feasibility of developing a risk assessment for the impact of climate change on the emergence of Crimean-Congo haemorrhagic fever in livestock in Europe: a Review

Abstract

Summary Crimean‐Congo haemorrhagic fever virus (CCHFV) is one of the most widespread of all medically important arboviruses with ticks of the Hyalomma spp. serving as the main vectors. Infection of livestock by CCHFV serves as a route of exposure to humans, as a reservoir of disease and as a route of importation. This study discusses the pathways and data requirements for a qualitative risk assessment for the emergence of CCHFV in livestock in Europe. A risk map approach is proposed based on layers that include the potential routes of release (e.g. by migrating birds carrying infected ticks) together with the main components for exposure, namely the distributions of the tick vectors, the small vertebrate host reservoirs and the livestock. A layer on landscape fragmentation serves as a surrogate for proximity of livestock to the tick cycle. Although the impact of climate change on the emergence of CCHF is not clear, comparing the distribution of risk factors in each layer currently with those predicted in the 2080s with climate change can be used to speculate how potential high‐risk areas may shift. According to the risk pathway, transstadial and/or transovarial transmission in the tick vector are crucial for CCHFV spread. Vector competence and tick vector switching, however, remain critical factors for CCHFV colonization of new regions in Europe. The species of migratory bird is also an important consideration in the release assessment with greater abundance and biodiversity of ground‐dwelling birds in southern Europe than in northern Europe.

Impact of climate change on risk of incursion of Crimean-Congo haemorrhagic fever virus in livestock in Europe through migratory birds

“…In this respect, the predictions from the current model may be too high because no allowance is made for failure of some of those larvae to survive and moult. Second, layers on the habitat suitability for H. marginatum (layer 3 in Gale et al 2010) and on the density of small mammal hosts, for example, hares, (layer 4 in Gale et al 2010) are not required for this incursion model. The value of p find will vary depending on the terrain and will also be affected by the species of birds which introduced that tick and in particular its favoured habitat and hence proximity to livestock.…”

“…The risk pathway is taken from Gale et al (2010) and involves three layers: l Layer 1 -abundance of migratory birds to predict the release of CCHFV through infected Hyalomma nymphs carried on migratory birds; l Layer 2 -temperature to predict the moult of nymphs to adult ticks; and l Layer 3 -Livestock density to estimate the probability of an adult tick finding a livestock host to feed upon.…”

“…This is an important consideration for developing a risk assessment (Gale et al 2010) because if migratory birds introduce immature ticks but only the adults feed on livestock, then a prerequisite for infection of livestock is that those immature ticks moult into adults before taking their next blood meal on a livestock animal. Certain temperature and humidity conditions are needed for moulting of immature stages of H. marginatum to adults (Estrada-Peña et al 2011).…”

“…It is nevertheless important for a number of reasons (Gale et al 2010). First, domestic ruminants may develop a transmissible viraemia following infection and hence amplify the pathogen in agricultural environments, thus serving as a reservoir for infection of feeding adult ticks (Sang et al 2011).…”

An Emerging Threat of Crimean Congo Hemorrhagic Fever: Call for Preparedness

“…Infestation of the immature stages of the ticks by small animals such as rabbits, hares, hedgehogs and rodents assist the maintenance of the virus in the lifecycle of the ticks (Gonzalez et al, 1992;Gargili et al, 2013). Feeding on the ground-dwelling birds, hares and hedgehogs drives larval and nymphal ticks to become infected with CCHFV, (Gale et al, 2010), while the adult ticks become infected while feeding on infected sheep, goats, cattle and pigs (Gale et al, 2010). Most species of birds play role as mechanical vectors in transportation of infected ticks, and appear to be refractory to CCHFV infection; but experimental studies in Ostriches have revealed the presence of the virus in for up to 1 to 4 days in blood and 5 days in visceral organs (Center for Food Security and Public Health (CFSPH), 2007).…”