In May 2022 an expanding cluster of Monkeypox (MPXV) infections was identified in various European countries. Unlike previously, this outbreak was predominately due to sexual transmission in men who have sex with men (MSM). Over 1000 cases have been diagnosed in 29 countries, including seven in Australia.
Monkeypox is a zoonotic viral infection that occasionally causes outbreaks, mostly in west and central Africa. Person-to-person transmission is by close contact, and sometimes by respiratory droplets and fomites. Disease is generally mild with a characteristic evolving vesicular rash, but death rates of 1-10% have been described in Africa. Intermittent MPXV identification has occurred in the UK and other countries over the last few years, generally associated with travel.
Monkeypox was first identified in 1958 and is in the Orthopoxvirus genus, related to smallpox (variola), cowpox and vaccinia. It has an approximately 196,000bp double-stranded DNA genome classified in two clades - West African and Congo Basin.
Diagnostic testing is by nucleic acid testing (NAT), either with a pan-Orthopox assay available in public health laboratories, or a MPXV-specific NAT. Other infections (HSV, VZV, molluscum, syphilis) with similar presentations may need exclusion. Whole genome sequencing has identified that the current outbreak (including the seven Australian cases) is of the West African clade. MPXV from Australian cases has been isolated in PC4 facilities at the ICPMR Westmead and VIDRL. There is a typical appearance on electron microscopy.
Smallpox vaccination probably provides some protection against MPXV, although the adverse effect profile of the older smallpox vaccines (eg. ACAM2000) is significant. Newer safer vaccines (JYNNEOS) are available and will be considered for high-risk groups, including relevant laboratory workers. Some antiviral drugs have in vitro MPXV activity, including cidofovir and brincidofovir. A newer agent, tecovirimat or T-poxx, has in vitro efficacy, but in vivo efficacy data is limited. Vaccinia immunoglobulin is available for immunocompromised individuals.
Monkeypox, following the emergence of SARS-CoV-2 and Japanese encephalitis virus, is another recent addition to public health concerns in Australia. It demonstrates how human behaviour may alter the mode of transmission of zoonotic viruses.