Susceptibility and transmission of mpox virus infection in brown rats (Rattus norvegicus).

Abstract

Mpox (formerly known as monkeypox) virus (MPXV) is the zoonotic pathogen of mpox disease in humans. Its increasing emergence outside of its endemic area has heightened the importance of investigating the virus' prevalence and maintenance in sylvatic reservoirs. The common brown rat (Rattus norvegicus) can inhabit almost anywhere in the UK, posing a threat to zoonotic transmission to humans. Two independent studies were carried out; the first investigated the susceptibility of brown rats to MPXV infection with a clade IIb mpox strain via two challenge routes: intranasal and intradermal. The second study considered the transmission of MPXV between challenged and naïve brown rats. All animals were asymptomatic to mpox disease, although enzyme-linked immunosorbent assay (ELISA) confirmed subclinical infection in challenge groups. In the susceptibility study, reverse transcription PCR (RT-PCR) detected mpox DNA in the lung tissue and throat swabs within the intranasally inoculated group, in addition to viable virus observed from the intranasal throat swabs. In contrast, no virus was detected in either tissues or swabs in the intradermally inoculated group or control group. RT-PCR results from the transmission study detected mpox DNA in tissues and throat swabs taken from challenged animals. Viable virus was observed from tissues and swabs of intranasally challenged animals with infectious titres of ~10²-10⁴ TCID₅₀ per millilitre. ELISA assays in the transmission study showed replicable results compared to the first susceptibility study in directly challenged animals alongside evidence of seroconversion in co-housed naïve animals. In conclusion, brown rats are susceptible to MPXV infection, as they have been demonstrated to maintain viable virus in the absence of clinical signs. Viral transmission of MPXV from infected rats to naïve rats was not observed by RT-PCR, although naïve rats did show antibody responses when exposed to infected rats indicating exposure to virus.