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:
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
Diagnosis of Lassa fever
Because the symptoms of Lassa fever are so varied, diagnosis can be difficult. Clinically, the disease can appear similar to other viral hemorrhagic fevers, including the Ebola virus, malaria and typhoid.
The only definitive tests for Lassa fever are laboratory-based where the handling of specimens can be hazardous; only specialized institutions can conduct these tests.3
Lassa fever is generally diagnosed by using enzyme-linked immunosorbent serologic assays (ELISA), which detect IgM and IgG antibodies and Lassa antigens. Reverse transcription-polymerase chain reaction (RT-PCR) can also be used in the early stages of the disease.
Treatment of Lassa fever
Lassa virus was first described in West Africa in 1969, in a village in Nigeria from which the disease takes its name.
If prescribed early on, the antiviral drug ribavirin has proven useful in fighting Lassa virus; to date, however, its mechanism of action is still subject to debate.4
During the course of the disease, it is important to manage fluid levels, electrolyte balance, oxygenation and blood pressure in the patient.
Unfortunately, access to ribavirin in the areas worst affected by the Lassa virus is limited. Additionally, ribavirin is potentially toxic and teratogenic (mutation-causing), making it a flawed solution.5
Ribavirin does not have a prophylactic capability and, currently, there is no vaccine for Lassa fever. However, work on a vaccine is underway, and some drugs are showing promise.
Prevention of Lassa fever
The primary drive in the prevention of Lassa fever is a general promotion of "community hygiene." Storing foods in rodent-proof containers, keeping garbage away from the home and keeping pet cats are the main recommendations.
The Mastomys rat is so widespread that it cannot realistically be eradicated. As a result, a push to avoid these rodents and dissuade them from sharing human habitation is vital.
The World Health Organization (WHO) and other organizations are constantly working to educate individuals living in areas where Lassa fever is a threat. People are being taught to avoid blood and other bodily fluids when caring for sick relatives. This education also extends to health care settings.
Basic hygiene standards, safe burying protocols and protective equipment including masks and eyewear are of the utmost importance.
The fight against Lassa fever is only just beginning; much more research will need to be carried out if treatments are to be found.
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