Guidance

Epidemiological case definitions for high consequence infectious disease mammarenaviruses

Published 13 August 2026

Guidance for healthcare professionals on when to suspect mammarenaviruses is available and should be the starting point for clinical assessment of a suspected case. This includes:

• Lassa virus
• Lujo virus
• Junin virus
• Chapare virus
• Machupo virus

Who this guidance is for

This guidance is for health protection teams (HPTs) for use in a mammarenavirus incident. It describes the categorisation of possible, probable and confirmed cases of high consequence infectious disease (HCID) mammarenaviruses. For the purposes of this guidance, mammarenaviruses include Lassa virus, Lujo virus, Junin virus (which causes Argentine haemorrhagic fever), Chapare virus, and Machupo virus (which causes Bolivian haemorrhagic fever).

In this guidance, ‘body fluids’ can include blood, vomit, faeces, urine, saliva and semen. 

For personal protective equipment (PPE) requirements for the management of HCID mammarenavirus cases, please see the ACDP guidance on the management of patients with viral haemorrhagic fever.    

Any individual who has not had contact with a potential source of an HCID mammarenavirus within the last 21 days before onset of illness is not deemed to be a possible or probable case.

Case definitions

Confirmed case

An individual (alive or deceased) with a positive laboratory test result (real-time polymerase chain reaction (PCR)) from a blood or other body fluid sample.

Probable case

An individual for whom no laboratory results are available (for example waiting for testing or results) where both of the following apply:

1. Clinical illness compatible with an HCID mammarenavirus [note 1] comprising fever (temperature greater than 37.5°C) with or without additional symptoms such as intense weakness, severe headache, myalgia, lethargy, abdominal pain, sore throat, vomiting, diarrhoea, unexplained haemorrhage, rash, shock or impaired consciousness.
2. History of direct contact with a probable or confirmed case of an HCID mammarenavirus or their body fluids in the 21 days before the onset of symptoms, without wearing adequate PPE or where there were breaches in PPE (for example category 3, 4 and 5 contacts as described in the mammarenavirus contact tracing matrix; this includes laboratory staff).

Possible case

A deceased individual with epidemiological risks for an HCID mammarenavirus [note 2]

Or:

An individual for whom no laboratory results are available (for example waiting for testing or results), where both of the following apply:

1. Clinical illness compatible with an HCID mammarenavirus [note 1] comprising fever (temperature greater than 37.5°C) with or without additional symptoms such as intense weakness, severe headache, myalgia, lethargy, abdominal pain, sore throat, vomiting, diarrhoea, unexplained haemorrhage, rash, shock or impaired consciousness.
2. History of direct contact with a confirmed case of an HCID mammarenavirus or their body fluids (including laboratory staff), but trained and wore appropriate PPE, and had no known breaches in PPE (for example category 1 and 2  contacts as described in the mammarenavirus contact tracing matrix).

Note 1: initial symptoms may be not specific, but onset can be sudden with symptoms worsening over a few days, often with lethargy, rash, evidence of capillary leak, bleeding/haemorrhage, shock and impaired consciousness.

Note 2: deceased individuals with an epidemiological link to the outbreak should be discussed with the Imported Fever Service (IFS) for consideration of post-mortem testing.