The host of Lassa virus is the “multimammate rat” ( Mastomys natalensis). Upon infection, the rodent is able to excrete the virus via urine for an extended period of time, and sometimes, for the rest of its life. Mastomys rodents breed freely, reproduce rapidly, and are found in abundance in the forests and savannas of central, west, and east Africa. In addition, multimammate rats readily colonize human homes and areas where food is easily accessible. These factors readily contribute to the rapid spread of the Lassa virus from infected mastomys rodents to humans.

People at risk of being infected by the Lassa virus are those who live in or frequently visit endemic regions such as Nigeria, Liberia, Sierra Leone, and other West African countries where multimammate rats are most commonly found. Equally, hospital staffs and care providers are at risk of being infected if the right protective measures and sterilization protocols are not observed.

Transmission of the virus occurs in two ways:

1. Rodent to Human: Humans become infected with the virus when they come in contact with the urine or feces of infected Mastomys rats through food. Contact with the virus may also occur when persons inhale tiny particles in the air already contaminated with the excretions of the infected rodent. This airborne transmission may occur during cleaning actions such as sweeping. People who consume the Mastomys rodent as food also ingest the virus along with it.

2. Human to Human: The Lassa virus can be spread from one person to the other through direct contact with the blood, faeces, urine, and other bodily fluids of a person infected with Lassa fever. Currently, there are no epidemiological evidences that support airborne transmissions between humans. However, sexual transmission of the Lassa virus has been reported. Cases of human to human transmission of the virus occur both in the community and hospital settings, where the virus is spread through the use of contaminated medical pieces of equipment such as re-used needles.

Lassa fever occurs in all age groups and affects both males and females. People living in communities and rural areas with poor sanitation where Mastomys rodents breed freely are at the greatest risk of infection. Similarly, health workers and care providers who are charged with the responsibility of taking care of Lassa fever patients are equally at risk if the right precautionary protocols are not duly followed.

Sources: These information were taken from various sources including World Health Organization (WHO)

How is Lassa fever treated and prevented? This will be explained at the next article