Further Assessment of Monkeypox Virus Infection in Gambian Pouched Rats ( Cricetomys gambianus) Using In Vivo Bioluminescent Imaging

Abstract

Monkeypox is a zoonosis clinically similar to smallpox in humans. Recent evidence has shown a potential risk of increased incidence in central Africa. Despite attempts to isolate the virus from wild rodents and other small mammals, no reservoir host has been identified. In 2003, Monkeypox virus (MPXV) was accidentally introduced into the U.S. via the pet trade and was associated with the Gambian pouched rat ( Cricetomys gambianus). Therefore, we investigated the potential reservoir competence of the Gambian pouched rat for MPXV by utilizing a combination of in vivo and in vitro methods. We inoculated three animals by the intradermal route and three animals by the intranasal route, with one mock-infected control for each route. Bioluminescent imaging (BLI) was used to track replicating virus in infected animals and virological assays (e.g. real time PCR, cell culture) were used to determine viral load in blood, urine, ocular, nasal, oral, and rectal swabs. Intradermal inoculation resulted in clinical signs of monkeypox infection in two of three animals. One severely ill animal was euthanized and the other affected animal recovered. In contrast, intranasal inoculation resulted in subclinical infection in all three animals. All animals, regardless of apparent or inapparent infection, shed virus in oral and nasal secretions. Additionally, BLI identified viral replication in the skin without grossly visible lesions. These results suggest that Gambian pouched rats may play an important role in transmission of the virus to humans, as they are hunted for consumption and it is possible for MPXV-infected pouched rats to shed infectious virus without displaying overt clinical signs.

Author Summary

Monkeypox virus is a close relative of Variola virus, the agent of smallpox, and causes a similar disease in humans, with classic pox skin lesions. Up to 10% mortality has been associated with some strains of monkeypox. Monkeypox disease occurs in central and west Africa. It is transmitted to humans from wild animals, but the reservoir species that maintains this virus in nature has not been identified. The Gambian pouched rat ( Cricetomys gambianus) was implicated as a possible source during the 2003 US monkeypox outbreak which resulted in human disease. To understand how the Gambian pouched rat could maintain and transmit the virus, six Gambian pouched rats were infected with Monkeypox virus engineered to express a marker gene, luciferase, which is detectable within the live animal via bioluminescence. Two animals served as uninfected controls. Viral shedding was quantified. Two of three animals infected via the intradermal route became clinically ill. Those infected intranasally showed no signs of disease, but the virus was detected in the nasal and oral cavities and distant sites within their bodies. All infected animals shed live Monkeypox virus. This study indicates that Gambian pouched rats could serve to transmit Monkeypox virus to humans in Africa.