Tick-Borne Transmission of Murine Gammaherpesvirus 68.

Herpesviruses are a large group of DNA viruses infecting mainly vertebrates. Murine gammaherpesvirus 68 (MHV68) is often used as a model in studies of the pathogenesis of clinically important human gammaherpesviruses such as Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. This rodent virus appears to be geographically widespread; however, its natural transmission cycle is unknown. Following detection of MHV68 in field-collected ticks, including isolation of the virus from tick salivary glands and ovaries, we investigated whether MHV68 is a tick-borne virus. Uninfected Ixodes ricinus ticks were shown to acquire the virus by feeding on experimentally infected laboratory mice. The virus survived tick molting, and the molted ticks transmitted the virus to uninfected laboratory mice on which they subsequently fed. MHV68 was isolated from the tick salivary glands, consistent with transmission via tick saliva. The virus survived in ticks without loss of infectivity for at least 120 days, and subsequently was transmitted vertically from one tick generation to the next, surviving more than 500 days. Furthermore, the F1 generation (derived from F0 infected females) transmitted MHV68 to uninfected mice on which they fed, with MHV68 M3 gene transcripts detected in blood, lung, and spleen tissue of mice on which F1 nymphs and F1 adults engorged. These experimental data fulfill the transmission criteria that define an arthropod-borne virus (arbovirus), the largest biological group of viruses. Currently, African swine fever virus (ASFV) is the only DNA virus recognized as an arbovirus. Like ASFV, MHV68 showed evidence of pathogenesis in ticks. Previous studies have reported MHV68 in free-living ticks and in mammals commonly infested with I. ricinus, and neutralizing antibodies to MHV68 have been detected in large mammals (e.g., deer) including humans. Further studies are needed to determine if these reports are the result of tick-borne transmission of MHV68 in nature, and whether humans are at risk of infection.

Transformation of Cells by Photoinactivated Murine Gamma-Herpesvirus 68 during Nonproductive and Quiescent Infection.

Infection of human MRC-5 cells and mouse NIH-3T3 cells with a murine gamma-herpesvirus (MuHV-4 strain 68; MHV-68) photoinactivated by visible light in the presence of methylene blue (MB) resulted in nonproductive infection and the appearance of morphologically transformed cells. Two stably transformed cell lines were derived from both of these cell types and were confirmed to contain both viral DNA and antigen. Next, a quiescent MHV-68 infection in MRC-5 and NIH-3T3 cells was established after cultivation at 41°C in the presence of phosphonoacetic acid. Following the exposure of quiescently infected cells to visible light for 120 s (5 times daily for 6 days) in the presence of MB, both MRC-5 and NIH-3T3 cells were observed to acquire transformed phenotypes. The cytopathic effect was observed in cells after 4-5 passages, after which the cells degenerated. However, when human interferon (IFN)-α and mouse IFN-ß were added to the media of quiescently infected MRC-5 and NIH-3T3 cells during the photoinactivating procedure, 2 stable transformed cell lines containing both viral DNA and the antigen were obtained and resembled those attained following nonproductive infection with photoinactivated virus.

Detection of Murine Herpesvirus 68 (MHV-68) in Dermacentor reticulatus Ticks.

Murid herpesvirus 4 (MuHV 4) strain 68 (MHV-68) is a natural pathogen of murid rodents, which serves as hosts to Dermacentor reticulatus ticks. These ticks are known to transmit multiple pathogens, which can cause diseases in humans and animals. Recently, the detection of MHV-68 antibodies in the blood of animals living in the same biotope as virus-infected mice has suggested the role of ticks in pathogen circulation in nature. Herein, to identify MHV-68 in D. reticulatus ticks, DNA samples from 432 adults were collected at two sites in southwestern Slovakia from 2011 to 2014. Samples were examined by polymerase chain reaction (PCR), targeting ORF50 of MHV-68. Ignoring season and locality, we have found 25.9 % of the male and 44.9 % of the female ticks to be positive. Within ticks collected in Vojka, 40 % (125/312) became positive, at a rate of approximately 6.8 times higher in spring than in autumn (66 vs 9.7 %). In addition, in the spring, 1.4 times more females were positive than males. Within ticks collected in Gabcíkovo, 23.3 % (28/120) became positive, with positive females being twice as frequent. The infecting virus was identified by analyzing amplified products via sequencing and restriction fragment length polymorphism (RFLP) analyses. Using an explantation/co-cultivation procedure, we examined the salivary glands, intestines, and ovaries of five females for live MHV-68. In all organs of two ticks, we identified a virus capable of replication in mammalian cells. This is the first report of MHV-68 detection in D. reticulatus ticks and of a live virus in their organs. Findings encourage further study to determine whether this potential arbovirus, found in salivary glands, is transmissible. It further supports the hypothesis regarding the mediating role of ticks in MHV-68 circulation in nature.