Lassa Fever, What You Should Know

 

Lassa fever is an illness caused by Lassa virus, a single-stranded RNA hemorrhagic fever virus from the family Arenaviridae. 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.

History

Though first described in the 1950s, the virus causing Lassa disease was not identified until 1969. 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. 
Lassa fever is a zoonotic disease, meaning that humans become infected from contact with infected animals. The animal reservoir, or host, of Lassa virus is a rodent of the genus Mastomys, commonly known as the “multimammate rat.” Mastomys rats infected with Lassa virus do not become ill, but they can shed the virus in their urine and faeces.
Because the clinical course of the disease is so variable, detection of the disease in affected patients has been difficult. When presence of the disease is confirmed in a community, however, prompt isolation of affected patients, good infection prevention and control practices, and rigorous contact tracing can stop outbreaks.
Lassa fever is known to be endemic in Benin (where it was diagnosed for the first time in November 2014), Ghana (diagnosed for the first time in October 2011), Guinea, Liberia, Mali (diagnosed for the first time in February 2009), Sierra Leone, and Nigeria, but probably exists in other West African countries as well.

Key facts

• Lassa fever is an acute viral haemorrhagic illness of 2-21 days duration that occurs in West Africa.

• The Lassa virus is transmitted to humans via contact with food or household items contaminated with rodent urine or faeces.

• Person-to-person infections and laboratory transmission can also occur, particularly in hospitals lacking adequate infection prevention and control measures.

• Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria, but probably exists in other West African countries as well.

• The overall case-fatality rate is 1%. Observed case-fatality rate among patients hospitalized with severe cases of Lassa fever is 15%.

• Early supportive care with rehydration and symptomatic treatment improves survival. 

          

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 of Lassa fever

The incubation period of Lassa fever ranges from 6–21 days. The onset of the disease, when it is symptomatic, is usually gradual, starting with fever, general weakness, and malaise. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain may follow. In severe cases facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract and low blood pressure may develop. 
Protein may be noted in the urine. Shock, seizures, tremor, disorientation, and coma may be seen in the later stages. Deafness occurs in 25% of patients who survive the disease. In half of these cases, hearing returns partially after 1–3 months. Transient hair loss and gait disturbance may occur during recovery.
Death usually occurs within 14 days of onset in fatal cases. The disease is especially severe late in pregnancy, with maternal death and/or fetal loss occurring in more than 80% of cases during the third trimester.

Prevention

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 eye wear