The Lassa virus is a virus of the Arenaviridae family. It is named after a town in northeastern Nigeria. The virus causes Lassa fever in humans following infection. The only natural host is the Natal multimammate mouse, an African rodent that occurs throughout Africa below the Sahara, but is only infected with the Lassa virus in West Africa. In some West African villages, 50 to 100 per cent of the animals carry the virus and infect 100,000 to 300,000 people annually with the Lassa virus.
Infected rodents excrete the pathogen via urine and other body secretions. The transmission to humans usually takes place through contaminated food, including consumption of the rodents. The virus can also enter the body via injured skin, mucous membrane or the respiratory tract.
Transmission from person to person is possible. The virus can also be transmitted through sexual contact and from a pregnant woman to her unborn child. The incubation period is three to 21 days.
Upon infection, the disease initially manifests itself in fever and flu-like symptoms. At this point, a diagnosis of Lassa fever is almost impossible. In general, the disease pattern is very similar to other tropical infectious diseases such as malaria.
A severe course of the disease is indicated by for example, oedema of the eyelids and the face, a painful inflammation of the pharyngeal mucosa, bleeding of the mucosa and fluid accumulation in the pericardium and chest. Neurological symptoms such as concentration disorders, visual disturbances and numbness are also signs that the course of the disease is becoming more severe. An irreversible state of shock with organ failure causes death on average 12 days after the onset of the disease. One to two percent of Lassa fever patients die from the consequences of the disease. So far, there is no vaccine against the disease.
For patients, strict isolation in specialised treatment centres is necessary, as this is an infectious disease of protection level 4. Within this framework, appropriate hygiene measures are taken and staff are equipped with specialised personal protective equipment.
The required spectrum of activity against Lassa viruses is: limited virucidal.