Lassa fever is an acute viral haemorrhagic illness caused by Lassa virus, a member of the arenavirus family of viruses.
Humans usually become infected with Lassa virus through exposure to food or household items contaminated with urine or faeces of infected Mastomys rats. The disease is endemic in the rodent population in parts of West Africa.
According to World Health Organization (WHO), Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, Togo and Nigeria, but probably exists in other West African countries as well.
Person-to-person infections and laboratory transmission can also occur, particularly in health care settings in the absence of adequate infection prevention and control measures.
Diagnosis and prompt treatment are essential. The overall case-fatality rate is 1%. Among patients who are hospitalized with severe clinical presentation of Lassa fever, case-fatality is estimated at around 15%. Early supportive care with rehydration and symptomatic treatment improves survival.
About 80% of people who become infected with Lassa virus have no symptoms. 1 in 5 infections result in severe disease, where the virus affects several organs such as the liver, spleen and kidneys.
Causes
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.
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.
