In a previous Outbreak Thursday post, the Outbreak Observatory team looked at the increased geo-temporal spread of Lassa fever in Nigeria. Since our post, the situation in Nigeria has markedly improved, with the number of Lassa fever cases decreasing from a high of 70 weekly reported cases in late-February to just five cases being reported at the end of last week. Notably, 37 healthcare workers (HCWs) have been infected with Lassa since the beginning of the outbreak, 8 of which died. Many of the HCW Lassa cases have come from those states that have been hit hardest by Lassa Fever, including Ebonyi, Ondo and Edo. Around 43% of the total reported cases among HCWs came from Ebonyi – the state whose total number of confirmed cases is almost double (175) that of the second highest state (Ondo with 98).

According to the WHO, there is no evidence that Lassa can be spread through airborne transmission. However, human-to-human transmission can occur through direct contact with the bodily fluids of an infected person, including through the use of contaminated medical equipment such as used needles. Early in the outbreak, there was a cluster of cases among HCWs in Ebonyi State. The WHO and the Nigeria Centre for Disease Control (NCDC) swiftly responded by providing medical supplies and medications as well as by deploying a Rapid Response Team to support response efforts and strengthen infection control measures. The cluster of cases among HCWs early on highlighted the importance of proper infection control practices for all patients, regardless of their presumed diagnosis.

Notably, the WHO reports that “phylogenetic analysis of 49 viruses detected during the 2018 outbreak [...] has shown evidence of multiple, independent introductions of different viruses and viruses similar to previously circulating lineages identified in Nigeria.” These results indicate that zoonotic transmission from rodents to humans is likely the biggest driver of the outbreak, with limited human to human transmission, and underscores the importance of vector control to mitigate the outbreak. However, the infection of HCWs involved in the care of Lassa patients indicates that risk of nosocomial transmission is possible and should also be a priority in containing the outbreak.

Photo: Depicts a training session, whereupon, Nigerian physicians were being taught by a member of the World Health Organization (WHO), the proper protocols to be followed when donning and removing personal protective equipment (PPE)

Photo Credit: CDC/Sally Ezra

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.