A chronological review of experimental infection studies of the role of wild animals and livestock in the maintenance and transmission of Crimean-Congo hemorrhagic fever virus

Abstract

This article provides a definitive review of experimental studies of the role of wild animals and livestock in the maintenance and transmission of Crimean-Congo hemorrhagic fever virus (CCHFV), the etiologic agent of Crimean-Congo hemorrhagic fever (CCHF), beginning with the first recognized outbreak of the human disease in Crimea in 1944. Published reports by researchers in the former Soviet Union, Bulgaria, South Africa, and other countries where CCHF has been observed show that CCHFV is maintained in nature in a tick-vertebrate-tick enzootic cycle. Human disease most commonly results from the bite of an infected tick, but may also follow crushing of infected ticks or exposure to the blood and tissues of infected animals during slaughter. Wild and domestic animals are susceptible to infection with CCHFV, but do not develop clinical illness. Vertebrates are important in CCHF epidemiology, as they provide blood meals to support tick populations, transport ticks across wide geographic areas, and transmit CCHFV to ticks and humans during the period of viremia. Many aspects of vertebrate involvement in the maintenance and spread of CCHFV are still poorly understood. Experimental investigations in wild animals and livestock provide important data to aid our understanding of CCHFV ecology. This article is the second in a series of reviews of more than 70 years of research on CCHF, summarizing important findings, identifying gaps in knowledge, and suggesting directions for future research.

The role of ticks in the maintenance and transmission of Crimean-Congo hemorrhagic fever virus: A review of published field and laboratory studies

“…Previous reviews have focused on epidemiology, molecular characterization, seroepidemiological studies, and the role of wild and domestic vertebrate animals in CCHFV maintenance and amplification of the infection (Bente et al, 2013; Spengler et al, 2016a, b; Zivcec et al, 2016). …”

“…While ticks are considered to be both vectors and reservoirs of CCHFV, due to the short-term viremia reported in vertebrates (Spengler et al, 2016b) and long-term survival in ticks, vertebrates are critical in viral ecology, serving as the bridges that the virus uses to pass from one tick to another and as viral amplifying hosts (Flick and Whitehouse, 2005; Shepherd et al, 1991; Swanepoel, 1998; Wilson et al, 1991). This concept is not new, and can be traced back to the pioneering studies of active foci in the Crimean Peninsula (Chumakov, 1947, 1948).…”

“…While most avian species may be refractory to CCHFV infection (EFSA, 2010; Swanepoel, 1998; Shepherd et al, 1987; Spengler et al, 2016a, b), migrating birds serve as sources of bloodmeals for immature ticks, and therefore provide a mode of dispersal of infected ticks, contributing to the spread and subsequent emergence of disease foci (Gale et al, 2012; Vorou, 2009). Long-distance movement of livestock may also contribute to dispersal of CCHFV-infected ticks because of the long feeding time of ixodid ticks (Rodriguez et al, 1997).…”

Crimean-Congo hemorrhagic fever and expansion from endemic regions

“…Although some borders prohibit movement of infected animals due to geographical or political reasons, cross-border movement of animals (especially livestock) is a frequent practice and may lead to the spread of disease. Notably, almost all livestock and wild vertebrates are susceptible to CCHFV infection but present no clinical signs [51 ● ], so current health screening border control practices do little to prevent movement of infected animals.…”

Second International Conference on Crimean-Congo Hemorrhagic Fever

“…In nature, vertebrates serve principally as hosts to the tick vector. They are susceptible to infection, but show no signs of illness (Spengler et al, 2016b). They develop a short-term viremia, contributing to maintenance and transmission of the virus in the tick population.…”