Monkeypox (Monkeypox Virus) Laboratory Case Definition (LCD)

The Public Health Laboratory Network have developed a standard case definition for the diagnosis of diseases which are notifiable in Australia. This page contains the laboratory case definition for Monkeypox Virus infection.

Page last updated: 27 May 2022

Introduction

Monkeypox virus is a poxvirus (Family Poxviridae, genus Orthopoxvirus; other members include variola and vaccinia viruses) with brick-shaped virions of 220–450 nm in length. Two clades of Monkeypox virus have been identified and named based on their geographical distribution (Congo Basin and West African clades). Monkeypox virus is considered the most important Orthopoxvirus capable of infecting humans since the eradication of smallpox (caused by variola virus).

Monkeypox is a zoonosis which can infect a range of mammalian species (including humans and non-human primates), but the natural reservoir remains unknown. Most cases have been reported in the Democratic Republic of the Congo and other central and western African countries. Monkeypox cases reported outside Africa have been linked to international travel or movement of animals, and secondary transmission has been reported. In 2022, a number of monkeypox cases were reported in Europe, the United Kingdom (UK) and United States (US) in men who have sex with men (MSM), prompting concern about potential to spread to Australia. As of 20 May 2022, two cases have been confirmed in Australia.

Monkeypox virus infection has an incubation period of 7–14 days (but can range from 5-21 days) and is characterised by a febrile prodrome with fatigue and headache, followed by the development of lymphadenopathy and a vesicopustular rash which can affect the face, palms/soles and mucosal surfaces. Localised rashes have also been described in the current outbreak involving MSM. Care is largely supportive, with mortality reported between 0–11% but there are significant challenges in accurately estimating this rate. Case fatality rates are lower for the West African clade compared to the Central African (Congo-Basin) clade. Clinical presentation is similar to smallpox, although the development of lymphadenopathy is generally not seen with smallpox.

Human-to-human transmission has been reported; the mechanism remains poorly characterised and has been linked to close physical contact, contaminated fomites and respiratory droplets. Transmission can also occur from direct contact with infected animals.

Vaccinia vaccination using a live-virus preparation of vaccinia virus (ACAM2000) is cross-protective against Orthopoxvirus infection and was used for widespread vaccination against smallpox. Epidemiological evidence suggests that vaccinia vaccination has some protection against monkeypox. In the US a newer vaccinia-based, live attenuated vaccine (JYNNEOSÔ) has also been specifically licensed for the prevention of monkeypox. Cessation of vaccinia vaccination worldwide (including in Australia) following smallpox eradication means that populations remain largely susceptible to Monkeypox virus infection.

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