Lassa fever: epidemic kills over 100 in Nigeria in the first months of the year

Publicação: 11 de March de 2020

The number of cases of the disease and the number of deaths continue to increase in the country

In 2019, alone, the disease killed about 170 people in Nigeria, and in the first weeks of 2020 more than 100 deaths were recorded

It has been half a century since Lassa fever was discovered in northern Nigeria, but health professionals in West Africa still need adequate equipment and training to safely manage patients of all ages affected by the disease, which represents a major challenge to public health on the continent, with Nigeria carrying the greatest burden. In 2019, alone, the disease killed about 170 people in Nigeria, and in the first weeks of 2020 more than 100 deaths were recorded The number of declared infected is higher than in 2019. The total number of cases across the country was 586 at the end of February.

Dr. Jason Kindrachuk, Assistant Professor of Viral Pathogenesis in the Department of Medical Microbiology at the University of Manitoba, Canada, explains that the increase in cases of Lassa fever (LASF) is not unexpected, as this is the time of year when there is usually an increase in the number of cases. In the last three years, the peak of cases of LASF occurred during the period between January and March and this trend seems to be the same this year. “LASF is a major public health challenge due to its unpredictability in terms of leakage events, the significant morbidity and mortality associated with infection and the inadequate testing and treatment capacity in the most vulnerable regions. All of these factors strengthen a global threat to public health with the Lassa virus”, he adds.

LASF is a significant public health threat and burden in some of the regions where resources are most limited, in Africa, and around the world. Outbreaks of LASF put considerable pressure on an already fragile health network. In addition, its treatment also represents a huge challenge due to the nature of the disease itself, because at first it looks like other diseases, such as malaria. “Ribavirin had variable efficacy compared to treatment with LASF. A recent systematic review concluded that treatment with this drug resulted in lower mortality rates than among those who did not receive treatment. Mortality appears to decrease if ribavirin is started intravenously within the first 6 days of the disease. This raised questions, given the non-specific nature of the initial symptoms of LASF, since delayed treatment has been associated with adverse outcomes”, pointed out Dr. Kindrachuk.

Challenge for diagnosis

Despite affecting up to 300 thousand people a year across West Africa, and causing more than 5 thousand deaths a year, Lassa fever is a little-known disease, difficult to diagnose and treat. Only a few laboratories in the affected areas can diagnose the virus. Nigeria, Africa’s most populous country, with about 200 million people, has five laboratories with the capacity to diagnose the disease. The diagnosis of LASF in the initial stage of the disease, based on the National Guidelines of the Disease Control Center of Nigeria for the Management of Lassa Fever Cases, is made mainly by testing biological samples of viral nucleic acid (RT-PCR) after qualifying for tests based on physiological symptoms of the disease. Serological tests and virus isolation are also used in this sense.

LASF also resembles several other diseases during the early stages of the disease and LASF may not be suspected until a patient has failed therapy targeting different pathogens. This creates a potential bottleneck in LASF testing and confirmation, as samples are later transferred to reference laboratories for evaluation. In addition, the significant diversity of the viral genome sequence of the virus isolates can also complicate the nucleic acid-based test with false negatives based on the inefficient matching of the primer/probe sets in the assays.”, explains Dr. Kindrachuk. Still according to him, the difficulty in efficient laboratory diagnosis is that it requires specialized laboratories, with the capacity and technical knowledge, to carry out various tests to confirm the LASF. Given the operating costs associated with increased capacity efforts, it may not be surprising and disheartening that these resources are limited.

The increase in the capacity of the national network of laboratories for the reliable and efficient diagnosis of suspected cases is of paramount importance, since only about 20% of the suspected cases of Lassa fever are generally diagnosed.

Main challenges regarding Lassa fever

For Dr. Kindrachuk, the main challenges to combat LASF outbreaks are in the attempt to increase both diagnostic and patient care capacities in Nigeria, as well as throughout West Africa. This requires a significant investment of funds from national and international communities. He also highlights the definitive need to increase international investment and funding for the identification of new therapies and vaccines for the virus. “In addition, increased community engagement strategies need to be employed to help build public trust among national and international public health officials and increase the capture of public message campaigns for LASF.”, he adds.

The spread of the disease across Nigeria, which may be the result of increased contact between humans and rodents, also poses a major challenge. Transmitted through the urine and feces of infected rats found in most tropical and subtropical countries in Africa, capable of contaminating anything with which they come into contact, the Lassa virus spreads through human contact with tissue, blood, body fluids, secretions or excretions. This includes coughing, sneezing, kissing, sexual intercourse and breastfeeding. In hospitals, the disease is transmitted by contaminated equipment. The disease can be fatal, but it can be treated if diagnosed early.

Unfortunately, zoonotic viruses are able to persist in the environment due to their very nature. The persistence of the virus in Mastomys rats makes leak prediction and control for humans extremely difficult, if not virtually impossible. This is no different from the difficulty encountered in trying to control leaks or persistence for viruses such as Ebola in bats. The large population of these animals creates an almost impossible scenario to try to eradicate the virus or interrupt the overflow events. In addition, the rodent host does not show signs of disease when infected, making it impossible to distinguish infected animals from those not infected just by appearance”, says Dr. Kindrachuk. The best control mechanisms require reducing contact with the host rodent and also with the animals’ urine or feces, as this can also carry the virus. The same also applies to household materials that may have come in contact with mice and their urine and feces. Increased public awareness and community engagement are needed in regions where the virus is endemic.

Finally, the professor points out that efforts to respond to infectious diseases across West Africa, including Nigeria, require greater community engagement in meaningful forums that create trust and respect cultural sensitivities. Increasing capacity at the local level in terms of response resources as well as experience will help in this way.

How to anticipate and respond to a Lassa fever epidemic

My opinion here is based on my experience with the Ebola virus. Anticipating events of repercussion to humans is a continuous area of research that has not yet been answered. Future response efforts, however, must rely on increasing regional and local capacities both in terms of diagnostic capacity and health infrastructure. This will require significant investments from national governments, as well as from the international community”, he acknowledges.

Lagos health officials said they diagnosed a case on February 17 which until the end of February was under control in a hospital. With more than 20 million inhabitants, Lagos is the most populous city in Nigeria. Sixty-three people who have been in contact with the patient and who may have been infected have been identified and are under surveillance. The Nigerian Academy of Sciences recently suggested that the declaration of a public health emergency would lead to a greater focus on combating LASF by the Nigerian government, including improving the national laboratory network and increasing funding for surveillance and response systems. This would also likely increase national acceptance that a long-term strategy is needed for both prevention and sustained control of future outbreaks. The authors noted that currently only 20% of suspected cases of LASF are eventually diagnosed.

Has adequate attention been paid to the disease over the years? The year of 2019 marked 50 years since the discovery of the virus that causes Lassa fever in the village of Lassa, Nigeria. The disease is endemic in West African countries, such as Nigeria, Sierra Leone, Guinea, Liberia and Benin. The fever is an acute viral hemorrhagic disease caused by the Lassa virus, a member of the arenavirus virus family.