Lassa virus

This is one of the most common rodents in equatorial Africa, found across much of sub-Saharan Africa. 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.

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 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. 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. 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. Cough and retrosternal pain are also common. Hemorrhagic symptoms develop is less than a third of individuals, but are associated with a significant raise in patient mortality.

Neurologic phenomena are less common than the aforementioned symptoms, but are nevertheless important. Aseptic meningitis, encephalitis, and global encephalopathy with seizures have all been documented in cases of Lassa virus infection. Intriguingly, deafness is a common feature during late-stage disease or early convalescence, and may be either ephemeral or permanent. Fatal cases or Lassa fever rarely show any signs of remission, progressing from fever to shock and death in an unrelenting slide.

Survivors remain symptomatic for approximately weeks following the onset of symptoms, whereupon the fever dissipates and the virus becomes undetectable in the blood.

Note that virus has still been found in the semen of surviving patients up to six weeks following infection. Treatment for Lassa fever is largely symptomatic. Management of bleeding and hydration is critical, especially in hemorrhagic cases. Pain management is prescribed through the use of opiates. Due to the permeability of blood vessels, pulmonary edema is a concern, and fluid infusion must therefore be carefully monitored.

Ribavirin has been employed principally in Lassa fever patients with poor prognoses, and is usually reserved for patients with an AST value above Though a harsh drug with significant side-effects, ribavirin is the drug of choice in cases of Lassa fever.

Transmission: Lassa virus is typically spread through aerosolized virus particles, via either infected rodents Mastomys natalensis or close contact with infected individuals. Diagnosis: Lassa fever is difficult to distinguish from other viral haemorrhagic fevers such as Ebola virus disease or yellow fever, as well as other diseases that cause a fever, including malaria or typhoid fever.

Diagnosis requires laboratory testing such as antigen detection tests or reverse transcriptase polymerase chain reaction RT-PCR assay, and samples needed be treated as extremely hazardous waste. The antiviral drug ribavirin can be effective against Lassa fever early on in the course of illness. There are no vaccines to protect against infection. This programme paved the way for the launch of a phase 1 trial of the Lassa vaccine candidate INO in February in Ghana.

Discouraging contact with the Mastomys rats and their urine or faeces, by storing food carefully and implementing rat control programmes as well as maintaining clean households reduces the risk of initial infection, but ensuring that health workers and laboratory staff are trained in infection prevention and control and biological containment can stop the infection spreading beyond the infected person. Speeding up vaccine development: Can we go from lab to jab in just days?

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