How is Lassa fever transmitted from person to person? I understand that Lassa fever is primarily spread to humans through contact with the urine or feces of infected Mastomys rats. However, I’m interested in specifically understanding the mechanisms and likelihood of person-to-person transmission. What are the specific routes (e.g., contact with bodily fluids, airborne transmission, sexual transmission) through which Lassa fever can spread from one human to another? Are there specific bodily fluids that pose a higher risk? What is the typical incubation period following person-to-person transmission, and what factors might increase the risk of transmission between individuals, such as proximity, duration of contact, or viral load in the infected individual?

Answer

Lassa fever is primarily transmitted to humans through contact with the urine or feces of infected Mastomys rats. However, person-to-person transmission can occur through direct contact with the blood, urine, feces, vomit, or other bodily fluids of a person infected with Lassa fever.

Specifically, person-to-person transmission can occur through:

• Direct contact with infected bodily fluids: This includes touching, kissing, or other close contact with the bodily fluids (blood, urine, feces, vomit, saliva, semen) of an infected individual. The virus can enter through broken skin or mucous membranes (eyes, nose, mouth).

• Contact with contaminated medical equipment: Inadequate sterilization or disinfection of medical equipment (needles, syringes, catheters, dialysis machines) can lead to transmission if the equipment is used on an infected person and then on a susceptible person.

• Sexual transmission: The Lassa virus has been detected in semen for several weeks or months after recovery, suggesting a potential risk of sexual transmission.

• Respiratory droplets (less common): While not the primary mode of transmission, it’s possible for the virus to spread through large respiratory droplets during close contact, especially in settings with poor ventilation.

• Caregiving settings: Healthcare workers and family members who care for Lassa fever patients without proper barrier precautions (gloves, gowns, masks, eye protection) are at high risk of infection.

• Laboratory exposure: Laboratory workers handling samples from Lassa fever patients or infected animals are at risk if proper biosafety protocols are not followed.

Factors that increase the risk of person-to-person transmission include:

• High viral load in the infected person: Individuals with severe Lassa fever typically have higher viral loads and are more likely to transmit the virus.

• Close and prolonged contact: The risk of transmission increases with the duration and intensity of contact with an infected person.

• Lack of barrier precautions: Failure to use personal protective equipment (PPE) greatly increases the risk of transmission.

• Poor hygiene: Lack of handwashing and proper sanitation practices can facilitate the spread of the virus.