Lassa fever is an acute, viral disease carried by a type of rat that is common in West Africa. It can be life-threatening.

It is a hemorrhagic virus, which means it can cause bleeding, although 8 out of every 10 people with the virus have no symptoms. If it affects the liver, kidneys, or spleen, it can be fatal.

The disease is endemic to a number of West African countries. Rough estimates suggest there are between 100,000 and 300,000 cases of Lassa fever each year in West Africa, and approximately 5,000 deaths due to the disease.

In some areas of Liberia and Sierra Leone, 10 to 16 percent of all hospital admissions are due to Lassa fever, indicating a serious and widespread impact in those areas.

In 2015, a person returning from Liberia to the U.S. received a diagnosis of Lassa fever. International travel has increased the risk of diseases spreading from one country to another.

This article will look at the causes, symptoms, diagnosis, and treatment of Lassa fever.

Fast facts on Lassa fever

  • Lassa fever causes around 5,000 deaths per year.
  • It is spread through the feces and urine of the multimammate rat (Mastomys natalensis).
  • It is most common in Sierra Leone, Liberia, Guinea, and Nigeria.
  • Symptoms are varied and include pulmonary, cardiac, and neurological problems.

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Lassa fever is a viral hemorrhagic disease. It can be serious.

Lassa fever was first discovered in Nigeria, when two missionary nurses became ill with 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 (M. natalensis).This is one of the most common rodents in equatorial Africa, found across much of sub-Saharan Africa.

Lassa fever mainly occurs in Sierra Leone, Liberia, Guinea, and Nigeria. However, the Mastomys rat is common in neighboring countries, so these areas are also at risk.

Once a Mastomys rat is infected with the virus, it can excrete the virus in its feces and urine, potentially for the rest of its life.

As a result, the virus can spread easily, especially as the rats breed rapidly and can inhabit human homes.

The most common method of transmission is by consuming or inhaling rat urine or feces. It can also be spread through cuts and open sores.

The rats live in and around human habitation, and they often come into contact with foodstuffs. Sometimes people eat the rats, 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. Sharing needles may spread the virus, and there are some reports of sexual transmission.

Lassa fever can also be passed between patients and staff at poorly equipped hospitals where sterilization and protective clothing is not standard.

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A cough can be a symptom of Lassa fever.

Symptoms generally appear within 6 to 21 days after infection occurs.

An estimated 80 percent of infections do not produce significant symptoms, although there may be a general malaise, headache, and a slight fever.

In the remaining 20 percent of cases, Lassa fever becomes serious.

Symptoms can include:

  • bleeding in the gums, nose, eyes, or elsewhere
  • difficulty breathing
  • a cough
  • swollen airways
  • vomiting and diarrhea, both with blood
  • difficulty swallowing
  • hepatitis
  • swollen face
  • pain in the chest, back, and abdomen
  • shock
  • hearing loss, which may be permanent
  • abnormal heart rhythms
  • high or low blood pressure
  • pericarditis, a swelling of the sac that surrounds the heart
  • tremors
  • encephalitis
  • meningitis
  • seizures

In around 1 percent of all cases, Lassa fever is fatal, and around 15 to 20 percent of all hospitalizations for the disease will end in death.

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 hearing loss, which occurs in around 1 in 3 infections.

This hearing loss varies in degree and is not necessarily related to the severity of the symptoms. Deafness caused by Lassa fever can be permanent and total.

It is particularly dangerous for women in the third trimester of pregnancy. Spontaneous loss of pregnancy occurs in around 95 percent of pregnancies.

The symptoms of Lassa fever vary widely, and diagnosis can be difficult.

Clinically, the disease can resemble other viral hemorrhagic fevers, including the Ebola virus, malaria, and typhoid.

The only definitive tests for Lassa fever are laboratory-based, and the handling of specimens can be hazardous. Only specialized institutions can conduct these tests.

Lassa fever is generally diagnosed by using enzyme-linked immunosorbent serologic assays (ELISA). These 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.

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Health organizations hope that current work on vaccine development will be successful.

Rehydration and treatment of symptoms can improve the chances of survival if there is an early diagnosis.

Prescribed early, the antiviral drug ribavirin has proven useful in fighting Lassa virus, but how it works remains unclear.

However, access to ribavirin in the areas worst affected by the Lassa virus is limited. Additionally, ribavirin may be toxic and teratogenic, meaning it can cause mutations. For this reason, it is not a perfect solution.

Ribavirin is not useful for preventing Lassa fever before it occurs, and there is currently no vaccine for this disease.

However, work on a vaccine is underway, and some drugs are showing promise.

An article published in The Lancet in April 2018 notes that the Coalition for Epidemic Preparedness Innovations (CEPI) and Themis Bioscience are collaborating on developing the Lassa vaccine through phase II clinical trials, and that research and development on the vaccine will be accelerated.

Media sources have expressed optimism that one vaccine may be ready for human trials by the end of 2018.

Other treatment focuses on relieving symptoms and maintaining body function.

This includes managing fluid levels, electrolyte balance, oxygenation, and blood pressure.

The main focus of prevention is "community hygiene," to control the rat population.

This includes:

  • regular hand-washing
  • storing foods in rodent-proof containers
  • keeping garbage away from the home
  • keeping pet cats
  • avoiding blood and other bodily fluids when caring for sick relatives
  • following safe burial procedures
  • using protective equipment in a healthcare setting, including masks and eyewear

The Mastomys rat is so widespread that it cannot realistically be eradicated. As a result, the main aim is to avoid these rodents and prevent them from sharing human habitation.

The World Health Organization (WHO) and other organizations work to raise awareness in areas where Lassa fever is a threat.