Experimental infection of golden hamsters with Guama virus (Peribunyaviridae, Orthobunyavirus)

Immunocompetent hamsters as a model for orthobunyavirus-induced neuroinvasion and neuropathology

BACKGROUND

Bunyavirus infections, including those caused by Bunyamwera serogroup orthobunyaviruses, represent a significant and yet likely still vastly underappreciated cause of mild to moderate human febrile infections. In severe cases, these infections can also cause neurological disease, particularly meningitis and encephalitis, and infection can even be fatal. However, with a few exceptions, information regarding the mechanisms underlying the neuroinvasion and neuropathogenesis of such infections is limited. This is due in part to a lack of animal models to facilitate such studies.

METHODOLOGY/PRINCIPAL FINDINGS

In an effort to develop an immunocompetent model of infection with Bunyamwera serogroup orthobunyaviruses, we infected 4-6-week-old female hamsters via either the intraperitoneal or subcutaneous route with 106 pfu/animal of Bunyamwera virus (BUNV), Batai virus or Ngari virus. Only BUNV infection resulted in clinical disease, which was characterized by weight loss, lethargy and neurological signs (i.e. tremor of the head or limbs, loss of righting reflex, "waltzing"). While symptoms were of similar severity for both routes, they occurred more frequently following subcutaneous inoculation. Consistent with these clinical signs, both antigen staining and histopathological abnormalities were found extensively throughout the brain.

CONCLUSIONS/SIGNIFICANCE

The reported hamster model of BUNV infection provides a new tool for studying orthobunyavirus infection, and particularly neuroinvasion and the development of neuropathology. This model is particularly significant because it makes use of immunologically competent animals and relies on a subcutaneous inoculation route that more closely mimics the natural infection route for arboviruses, thereby providing a more authentic cellular and immunological context at the initial site of infection.

Viral Ecology and Natural Infection Dynamics of Kaeng Khoi Virus in Cave-Dwelling Wrinkle-Lipped Free-Tailed Bats (Chaerephon plicatus) in Thailand

Kaeng Khoi virus (KKV; Order: Bunyavirales), is an endemic viral infection of the wrinkle-lipped free-tailed bat (Chaerephon plicatus aka Tadarida plicata plicata). Little is known about the ecology and maintenance of KKV within the bat population, nor the infection dynamics and transmission among bats or between bats and other vertebrates. Therefore, KKV was studied in Kaeng Khoi cave, Saraburi province, Thailand, during 1973–1974 with the objectives to (1) characterize the seasonal infection rates of KKV in the context of the bat population ecology, and (2) describe the infection dynamics and viral shedding by naturally- and experimentally-infected bats. To this end, the free-tailed bat population was estimated by a series of timed photographs taken during the evening exodus. The case population of 900,000 adult bats doubled at the time of weaning of the young and returned to its previous level soon thereafter. The newborn bats had neutralizing antibodies to KKV that were likely to be maternal in origin. The KKV antibody prevalence in adult bats was high (69–91%) in March–May and low (29–40%) in August and September. Kaeng Khoi virus was isolated from 75% of dead and 50% of moribund bats, but was not found in nearly 400 apparently healthy bats. Virus was present in saliva, urine and blood of most of the naturally-moribund bats tested. Consistent with observations from naturally-infected bats, experimental infection of bats with KKV revealed significant liver pathology, also suggestive that this is not a benign infection. Kaeng Khoi virus is an endemic, year-round infection maintained by the annual recruitment of a large number of immunologically-naïve juvenile bats. Moreover, it produces an acute infection in the bat, either leading to death by hepatitis, or immunity.

Pathogenesis and Immune Response of Ebinur Lake Virus: A Newly Identified Orthobunyavirus That Exhibited Strong Virulence in Mice

Orthobunyaviruses are a group of viruses with significant public and veterinary health importance. These viruses are mainly transmitted through mosquito-, midge-, and tick-vectors, and are endemic to various regions of the world. Ebinur Lake virus (EBIV), a newly identified member of Orthobunyavirus, was isolated from Culex mosquitoes in Northwest China. In the present study, we aimed to characterize the pathogenesis and host immune responses of EBIV in BALB/c mice, as an animal model. Herein, we determined that BALB/c mice are highly susceptible to EBIV infection. The infected mice exhibited evident clinical signs including weight loss, mild encephalitis, and death. High mortality of mice was observed even with inoculation of one plaque-forming unit (PFU) of EBIV, and the infected mice succumbed to death within 5-9 days. After EBIV challenge, rapid viremic dissemination was detected in the peripheral tissues and the central nervous system, with prominent histopathologic changes observed in liver, spleen, thymus, and brain. Blood constituents' analysis of EBIV infected mice exhibited leukopenia, thrombocytopenia, and significantly elevated ALT, LDH-L, and CK. Further, EBIV infection induced obvious cytokines changes in serum, spleen, and brain in mice. Collectively, our data describe the first study that systematically examines the pathogenesis of EBIV and induced immune response in an immunocompetent standard mouse model, expanding our knowledge of this virus, which may pose a threat to One Health.