What is the risk of a dangerous outbreak of Lassa fever in Africa?

During the first three weeks of 2023, the Nigerian Center for Disease Control and Prevention (NCDC) reported 244 confirmed cases of Lassa fever in 16 states of the country, with 37 deaths and a fatality rate of 15.1%. This situation suggests an unprecedented upward trend in the number of reported confirmed cases compared to previous years. That is why the 2nd level of the multidisciplinary National Operational Center for Combating Lassa Fever has been activated.

The first patient was a missionary nurse.

Lassa fever is an often fatal viral hemorrhagic fever caused by the Lassa virus. The disease was described in the 1950s, and the first human infection with Lassa virus was reported in 1969. The patient was a missionary nurse who became infected while working in a rural hospital near the northern village of Lassa, Nigeria.

The nurse died after being transported to the city of Jos, more than 600 kilometers away, for treatment at Bingham Hospital, established by American missionaries.

In Jos, two other nurses became infected and also died. A third nurse, Lily (Penny) Pinneo, who cared for the previous ones, also became ill but survived the infection after she was taken to New York Presbyterian Hospital. This made her the first known victim to survive the disease.

Blood samples from infected nurses were tested at Yale University, where the Lassa virus was first isolated. The Pinneo isolate was designated as the type strain. Two Yale University researchers contracted the virus during these initial studies, and one of them died.

This early experience with the Lassa virus has spurred the development of improved efforts to study new pathogens, including the construction of high biosecurity laboratories that operate under strict regulations and oversight.

The Lassa virus is an enveloped, single-stranded RNA virus with two negative strand segments belonging to the Arenaviridae family. Rodents, especially the African soft-haired rat (mastomys natalensis) are considered natural hosts of the virus. Kinds Mastomys erythroleucus, hylomiscus pamphi And Moose Bauley (pygmy mice) have also been found as important reservoirs.

Rodents excrete the virus in their urine and feces, and direct contact with these materials, such as touching dirty objects, eating contaminated food, or contact with open cuts or sores, can lead to infection.

Transmission of the Lassa virus to humans usually occurs by ingestion or inhalation of contaminated material. But there is also person-to-person transmission that can occur after contact with the blood, tissues, secretions, or secretions of a person infected with the Lassa virus.

African soft-haired rats often breed, produce large numbers of offspring and are numerous in the savannas and forests of West, Central and East Africa. In addition, he has the ability to colonize human homes and places where food is stored. All these factors contribute to the relatively efficient spread of the Lassa virus from infected rodents to humans. The disease is common in Sierra Leone, Ghana, Mali, Nigeria, Benin, Togo, Guinea and Liberia. Especially during the dry season, from November to April.

Some simple preventive measures are based on promoting good “public hygiene” to keep rodents out of homes. This includes keeping grains and other foodstuffs in rodent-proof containers, throwing trash away from home, cleaning homes, and even keeping cats as a control method.

hard to define

Identification of the onset of the disease is often difficult because it presents with generalized symptoms and a nonspecific clinical presentation: fever, vomiting, fatigue, abdominal pain, sore throat, chest pain, and myalgia. It can then progress to serious complications such as encephalitis, respiratory distress, bleeding, neurological problems, and hearing loss.

The incubation period of the disease is usually 7 to 10 days, up to a maximum of 21 days. The infection is mild or asymptomatic in 80% of cases. As a rule, lethality in Lassa fever is 1-2%. The number of Lassa virus infections in Africa is estimated to be between 300,000 and 500,000 each year, with approximately 5,000 deaths.

Unfortunately, these estimates are rough because case surveillance is not uniform. Therefore, the mortality rate may be underestimated. In fact, some outbreaks of the virus are known to have reached mortality rates of over 20%. Approximately one third of survivors develop sudden onset sensorineural hearing loss. In endemic countries where access to hearing aids is limited, hearing loss causes a reduction in the quality of life of those affected and a burden on society and public health. Hearing loss is estimated to cost Nigeria $43 million a year.

In addition, the Lassa virus has a high affinity for the placenta and vascular tissues, which is why the mortality of women in the third trimester of pregnancy is especially high. Spontaneous abortion is a serious complication of infection and is estimated to be responsible for 95% of fetal deaths of infected pregnant mothers.

There is currently no vaccine that protects against Lassa fever, but the antiviral ribavirin appears to be an effective treatment if given early in the clinical course of the disease.

A local outbreak can become a pandemic

Lassa fever continues to pose a threat to endemic and non-endemic countries. People traveling to areas where outbreaks are occurring should avoid contact with rodents, food and drink potentially contaminated with rodent feces, and contact with people who have symptoms of hemorrhagic fever.

Public health experts should remain vigilant for the possibility of imported cases of Lassa fever and ensure early diagnosis to prevent secondary transmission. Recent experience has shown us that a local outbreak can become a global pandemic. Therefore, it is important to implement strategies focused on OneHealth (One Health) to improve surveillance and prevention, and to promote research into the development of new antivirals and vaccines.

Of course, the implementation of public policies to rebuild the public health infrastructure and strengthen fragile health systems in Africa is critical to preventing and containing future outbreaks of new infectious diseases emerging on the African continent.

Raul Rivas Gonzalez, professor of microbiology, University of Salamanca

This article was originally published on The Conversation. Read the original.