A Novel Mode of Arbovirus Transmission Involving a Nonviremic Host

Abstract

In nature, infected and uninfected arthropod vectors often feed together on an animal. In mimicking this scenario in the laboratory, uninfected vectors were found to acquire virus while cofeeding on the same host as infected vectors. However, the vertebrate host on which they fed did not develop detectable levels of virus in its blood. These observations were made with Thogoto virus, an influenza-like virus of medical and veterinary significance. Rhipicephalus appendiculatus ticks were used as the vector and guinea pigs as the vertebrate host. The results demonstrate that a vertebrate that is apparently refractory to infection by an arthropod-borne virus can still play an important role in the epidemiology of the virus, and they suggest a novel mode of arthropod-borne virus transmission.

Viraemic transmission of Crimean-Congo haemorrhagic fever virus to ticks

“…Consequently, it is more difficult to quantify threshold levels of viraemia for ticks with any accuracy although it is generally accepted that the probability of viral transmission to feeding ticks is directly proportional to the intensity of viraemia in the host [18,19]. Recently, however, Jones and colleagues [20] have shown transmission of Thogoto virus to uninfected Rhipicephalus appendiculatus which were co-fed with infected ticks on hosts in which viraemia was undetectable. This 'non-viraemic' transmission was enhanced by factors present in tick salivary glands [21].…”

Empirical evidence for key hosts in persistence of a tick-borne disease

“…TBE provides a good model system for testing our hypotheses since we can use non-invasive means of identifying potential TBE transmission. TBE virus is transmitted to susceptible ticks when they feed adjacent to infected ticks, through a process known as co-feeding which does not involve virus amplification within the host (Jones et al, 1987;Labuda et al, 1993). Transmission is facilitated by tick saliva and occurs only on specific hosts, for example, A. flavicollis (Labuda et al, 1997) and depends on cellular events such as invasion of immune cells that are transported to the lymph nodes.…”

Nonviremic transmission of West Nile virus

“…Because susceptible, insusceptible, and immune hosts can support NVT (6)(7)(8), the population of vertebrates that may contribute to the WNV transmission cycle is probably much greater than was previously realized. Furthermore, with no requirement for a latent incubation period in the vertebrate, because virus can be directly transmitted from one mosquito to another, the transmission process is accelerated.…”

“…The discovery of NVT challenged the paradigm that arboviruses are transmitted only by arthropods feeding on viremic hosts. NVT was first observed with ticks cofeeding on rodents (6)(7)(8)(9), which was subsequently demonstrated by Mead et al (10) for vesicular stomatitis virus (VSV) between cofeeding black flies, but has not previously been reported for mosquitoes. Our hypothesis for this study was that the quantity of WNV secreted in the saliva of infected mosquitoes is sufficiently high to infect adjacent cofeeding mosquitoes directly without the requirement for replication in the vertebrate host.…”