Lassa fever: frequently asked questions for the general public

What is Lassa fever?
Lassa fever is a viral infection caused by Lassa virus. It is the most common viral haemorrhagic fever. Lassa fever is regularly found in parts of West Africa including Guinea, Liberia, Sierra Leone and Nigeria. 

What are the symptoms of Lassa fever?
Approximately 80% of people infected with Lassa virus do not develop any symptoms. The other 20% of people infected with Lassa virus develop Lassa fever, which is a viral haemorrhagic fever. The time between being infected with Lassa virus and developing symptoms is usually between 6 and 21 days. Symptoms appear gradually and include fever, general weakness, tiredness, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough and stomach pain. Severe cases may have facial swelling, fluid in lungs, bleeding from multiple sites and low blood pressure. Shock, seizures, shaking, confusion and coma may occur in later stages. Elderly people and those with weakened immune systems e.g. people living with cancer, may have more severe symptoms, but full recovery is usual.

Following recovery, the most common complication is deafness, which occurs in approximately 33% of cases. Patients can also experience temporary hair loss and develop an unusual way of walking during recovery.

The overall case fatality rate is 1%. In those who are hospitalised, approximately 15-20% of patients die. The death rates are particularly high in women in the third trimester of pregnancy and in foetuses of infected mothers, 95% of whom die before birth.

How is Lassa virus spread?
Lassa virus is primarily spread through direct contact with the urine and/or faeces of the multimammate rat. This rat is commonly found in Africa and is not found in Ireland. Infection can also occur following inhalation of particles containing Lassa virus e.g. from an infected person coughing. Person to person spread can occur via infected blood or bodily fluids. Sexual transmission has been reported and the virus has been found in semen up to 3 months after infection. The virus has also been found in urine up to 32 days following infection.

How is infection with Lassa virus diagnosed?
In Ireland, Lassa virus can be detected in the blood and urine (by PCR testing) of infected individuals. This PCR test can be performed at the National Virus Reference Laboratory (NVRL). However, serology (IgM) is the mainstay of diagnosis. Serological (IgM) and confirmatory testing on all samples is carried out at the Rare & Imported Pathogens Laboratory (RIPL), Porton Down, UK.

Have cases of Lassa fever been diagnosed in Ireland?
Lassa fever has never been diagnosed in a person in Ireland.

How is Lassa fever treated?
There is no vaccine against Lassa fever. Patients with Lassa fever may be treated with ribavirin, an antiviral drug shown to be most effective when given in the early stages of illness. Patients may also require intensive supportive therapy including intravenous fluids, maintaining their oxygen status and blood pressure.

Are people in Ireland at risk of Lassa fever?
It is possible that Lassa virus could be imported into Ireland in a traveller returning from an affected country. While the virus is primarily spread by contact with the urine and faeces of the multimammate rat (not found in Ireland), the virus can be spread through inhalation of the virus and by person to person spread via infected blood and body fluids.

What countries are affected by Lassa virus?
Lassa fever is regularly found in parts of West Africa including Guinea, Liberia, Sierra Leone and Nigeria. The multimammate rat, which sheds the virus in its urine and faeces are often numerous in rural areas of West, Central and East Africa and frequently live in people’s homes.

What is the current travel advice?
The Department of Foreign Affairs and Trade (DFA) provides guidance to travellers that is updated regularly. Please consult the DFA website at https://www.dfa.ie/travel/travel-advice/ and click on the relevant country. It is important to check this information prior to any trips, as the situation could change rapidly.

What do I do if I am living/working in an area where Lassa virus is present?
If you live in an affected area you should take measures to protect yourself from contracting Lassa fever by avoiding:

• consumption of food and drink contaminated with rodent droppings
• exposure to rodents
• contact with patients who have viral haemorrhagic fever

If you become ill, you should contact your local health care provider by phone for initial assessment letting him/her know of your recent travel history to an area where Lassa fever is circulating. They will be able to advise you on your individual circumstances.

What do I do if I am travelling to an area where Lassa virus is circulating?

• All travellers going to an area affected by Lassa fever should take measures to protect themselves from contracting Lassa fever by avoiding:
  • consumption of food and drink contaminated with rodent droppings
  • exposure to rodents
  • contact with patients who have viral haemorrhagic fever
• Irish citizens who live in the affected areas should take measures to protect themselves from contracting Lassa fever by avoiding:
  • consumption of food and drink contaminated with rodent droppings
  • exposure to rodents
  • contact with patients who have viral haemorrhagic fever
• People showing symptoms suggestive of Lassa fever while in countries where Lassa virus is circulating should seek medical advice from a health care provider by phone for initial assessment, letting them know of any recent travel history.
• In healthcare settings, healthcare workers should consistently implement standard infection prevention and control measures when caring for all patients and implement additional infection control procedures including appropriate personal protective equipment for Lassa fever confirmed patients.

Please see further travel advice on the HPSC website at www.hpsc.ie 

What do I do if I am returning to Ireland from an area where Lassa virus is circulating?
If you become ill upon your return to Ireland, you should contact your doctor by phone for initial assessment and let him/her know of your recent travel history to an area where Lassa fever is circulating. They will be able to advise you on your individual circumstances.

Last updated: 28 May 2018