Influence of laboratory animal hosts on the life cycle of Hyalomma marginatum and implications for an in vivo transmission model for Crimean-Congo hemorrhagic fever virus

Abstract

Crimean-Congo hemorrhagic fever virus (CCHFV) is one of the most geographically widespread arboviruses and causes a severe hemorrhagic syndrome in humans. The virus circulates in nature in a vertebrate-tick cycle and ticks of the genus Hyalomma are the main vectors and reservoirs. Although the tick vector plays a central role in the maintenance and transmission of CCHFV in nature, comparatively little is known of CCHFV-tick interactions. This is mostly due to the fact that establishing tick colonies is laborious, and working with CCHFV requires a biosafety level 4 laboratory (BSL4) in many countries. Nonetheless, an in vivo transmission model is essential to understand the epidemiology of the transmission cycle of CCHFV. In addition, important parameters such as vectorial capacity of tick species, levels of infection in the host necessary to infect the tick, and aspects of virus transmission by tick bite including the influence of tick saliva, cannot be investigated any other way. Here, we evaluate the influence of different laboratory animal species as hosts supporting the life cycle of Hyalomma marginatum, a two-host tick. Rabbits were considered the host of choice for the maintenance of the uninfected colonies due to high larval attachment rates, shorter larval-nymphal feeding times, higher nymphal molting rates, high egg hatching rates, and higher conversion efficiency index (CEI). Furthermore, we describe the successful establishment of an in vivo transmission model for CCHFV in a BSL4 biocontainment setting using interferon knockout mice. This will give us a new tool to study the transmission and interaction of CCHFV with its tick vector.

Keywords: BSL4; Crimean-Congo hemorrhagic fever; Crimean-Congo hemorrhagic fever virus; Hyalomma marginatum; bunyavirus; tick; tick-borne virus; transmission.

Figure 1

Geographic distribution of Hyalomma marginatum based on (Hoogstraal, 1979), www.kolonin.org and http://www.efsa.europa.eu/en/efsajournal/pub/1723.htm (both accessed April 2013).

Figure 2

Life cycle of Hyalomma marginatum under laboratory conditions when feeding on mice, guinea pigs, and rabbits. Colored segments represent time periods required for different life stages. Bars represent range of values. Values were not compared statistically.

Figure 3

Molting larvae and newly emerged nymphs feeding on guinea pig (top) and rabbit (bottom). Red arrows indicate molting larvae. White arrows show ruptured cuticles left from molted and emerged larvae still attached to the skin. Newly emerged nymphs feeding in close proximity to where they fed as larvae (black arrow).

Figure 4

Summary of oviposition data (A–F). Newly deposited egg mass weights measured daily of the females fed on mice (A), guinea pigs (B), and rabbits (C). Each color represents an individual female. Comparisons of egg mass to engorged weight (D) and weight gain to conversion efficiency index (CEI) in (E). (F) Comparison of the engorged weights, total egg mass weights, and weight gains (%) of the females fed on the three different hosts. For D–F, data are color-coded in gray for mice, orange for guinea pigs, and blue for rabbits.