Role of brown rats in transmission of Mpox virus

The Monkeypox virus (MPXV) can infect a wide range of mammalian species, however no known animal reservoir currently exists outside of Africa. A significant concern during the 2022/2023 outbreak was the potential for MPXV to infect a new host species, creating a new animal reservoir outside of Africa through spillback from infected humans to pest, their pets or livestock. These infected animals in turn may become reservoirs and transmit the virus back to humans. The detection of MPXV in waste water added to the potential risk of brown rats, which often live in sewers, becoming a reservoir for this virus. WBVR researchers in collaboration between ISIDORe, Veterinary Biocontained Facility Network (VetBioNet) and National Institute for Public Health and the Environment (RIVM) investigated the susceptibility of rats to MPXV. In addition, the disease progression, viral shedding and transmission potential was characterized.

Study

To determine whether rats are susceptible to infection with MPXV, the animals were experimentally inoculated with a clinical isolate of MPXV clade IIb. The development of clinical disease was monitored and tissues were examined to establish virus distribution and pathology. Furthermore, as an indicator of virus spread the presence of viral genomic DNA in swabs of nose, throat, rectum and skin was assessed using qPCR.

Following inoculation, the researchers found skin lesions from day 4 post inoculation at the site of scarification. These lesions were detectable up to day 11. The animal showed no other clinical signs of disease such as weight loss or fever.

In the majority of animals low levels of viral genome were detected in nose swabs 6 days post inoculation. Higher levels of viral genome were detected in throat swabs, with peak shedding 6 or 8 days after inoculation. Infectious virus was only detected by virus isolation on Vero cells on day 6. This corresponded with the highest genome loads. Although more variable, skin swabs were also positive for viral genome as early as 4 days post infection.

Model

The research team concludes that rats are susceptible to MPXV clade IIb infection. Infected rats shed virus via their respiratory tract and skin lesions. “The role of brown rats in the transmission chain of MPXV in the field is yet to be determined”, stresses Barry. “However, the outcome of our research in light of the ongoing multi-country outbreak of clade I MPXV, shows that the rat offers a potential new infection and disease model. Our model recapitulates the disease seen in the majority of human cases and can therefore be used for preclinical evaluation of countermeasures against MPXV.

Public health emergency

Mpox is a zoonotic disease caused by monkeypox virus (MPXV) and is currently the most prevalent orthopoxviral infection in humans after the eradication of smallpox. The World Health Organization (WHO) declared mpox a Public Health Emergency of International Concern (PHEIC).