Lassa fever is a viral disease carried by the multimammate rat (Mastomys natalensis). Its symptoms are incredibly varied and it can often be fatal.
The disease is endemic to a number of West African countries. There are estimated to be between 100,000 and 300,000 cases of Lassa fever per year and approximately 5,000 deaths due to the disease. However, these are only crude estimates as the reporting of cases is not consistent across all areas.
In some areas of Liberia and Sierra Leone, 10-15% of all hospital admissions are due to Lassa fever, indicating a serious and widespread impact in those areas.1
Recent cases of Lassa fever in Germany, the Netherlands, the UK and US in travelers on commercial airlines have demonstrated the potential of this highly dangerous and contagious pathogen to spread.
In this article, we will cover Lassa fever's causes, symptoms, diagnosis and treatment.
Contents of this article:
Fast facts on Lassa fever
Here are some key points about Lassa fever. More detail and supporting information is in the main article.
- Lassa fever causes around 5,000 deaths per year
- Lassa fever is spread by the multimammate rat (Mastomys natalensis)
- Sierra Leone, Liberia, Guinea and Nigeria are worst affected by Lassa fever
- Mastomys rats spread the virus via their feces and urine
- Lassa fever's symptoms are varied and include pulmonary, cardiac and neurological problems
- Diagnosis of Lassa virus can be challenging because of its wide array of symptoms
- Around 15%-20% of Lassa fever hospitalizations end in death
- Only 20% of infections cause severe symptoms
- There is no vaccine for Lassa fever currently available.
What is Lassa fever?
Lassa fever is spread by the multimammate rat, a common rodent found across much of sub-Saharan Africa.
The illness was first discovered in Nigeria when two missionary nurses succumbed to the virus in 1969. Its name is derived from the village of Lassa where it was first documented.
Lassa fever is a viral infection carried by the multimammate rat (Mastomys natalensis), one of the most common mice in equatorial Africa found across much of sub-Saharan Africa.
Lassa fever is predominantly reported in Sierra Leone, Liberia, Guinea and Nigeria but, because of the Mastomys rat's high prevalence in neighboring countries, these areas are also at risk.
Once a Mastomys rat is infected, it can excrete the virus in its urine, potentially for the rest of its life. This makes the spread of the disease worryingly easy when added to the fact that this species, like other rats, breeds easily and inhabits human homes.
The most common method of transmission is the consumption or inhalation of rat urine or feces. Lassa fever can also be spread through cuts and open sores.
Because the rats live in and around human habitation, they often come into contact with foodstuffs. The rats themselves are sometimes eaten and the disease can be spread during their preparation.
Person-to-person contact is possible via blood, tissue, secretions or excretions, but not through touch. Lassa fever can also be passed between patients and staff at poorly equipped hospitals where sterilization and protective clothing is not standard.
Symptoms of Lassa fever
Symptoms generally appear within 1-3 weeks following infection. An estimated 80% of infections produce symptoms so mild that they remain undiagnosed. These mild infections are characterized by a general malaise, headache and a light fever.
For the 20% of cases where Lassa fever becomes serious, symptoms can include:
- Hemorrhaging - in the gums, nose, eyes or elsewhere
- Difficulty breathing
- Swollen airways
- Vomiting and diarrhea (both bloody)
- Difficulty swallowing
- Swollen face
- Pain in chest, back and abdomen
- Hearing loss (sometimes permanent)
- Abnormal heart rhythms
- Hypertension or hypotension
- Pericarditis (a swelling of the sac that surrounds the heart)
Death can occur within 2 weeks after the onset of symptoms due to multiple organ failure. One of the most common complications of Lassa fever is deafness, occurring in around one third of cases. The deafness varies in degree and is not necessarily related to the severity of the symptoms. Deafness caused by Lassa fever can be permanent and total.
An estimated 15%-20% of Lassa fever hospitalizations end in death, although, in total, only 1% of infections end in fatality. Women in the third trimester of their pregnancy have particularly high death rates. An estimated 95% of fetuses die if the mother becomes infected.2
On the next page, we look at the diagnosis, treatment and prevention of Lassa fever.