There is no denying the fact that since the resurgence of Lassa fever in Nigeria was recently reported in the media that it has become a cause for concern to many Nigerians that are well informed about the disease. The reason for the concern cannot be farfetched as its devastating effect to human life is imponderable and the conflicting reports on its control in the country.
Overview of Lassa fever
Lassa fever is an acute viral illness that occurs in West Africa. The illness was discovered in 1969 when two missionary nurses died in Nigeria. The virus is named after the town in Nigeria where the first cases occurred. The virus is a member of the virus family Arenaviridae, is a single-stranded RNA virus and is zoonotic.
Lassa fever is endemic in parts of West Africa including Sierra Leone, Liberia, Guinea and Nigeria; however, other neighbouring countries are also at risk, as the animal vector for Lassa virus, the “multimammate rat” (Mastomysnatalensis) is distributed throughout the region.
Signs and symptoms of Lassa fever
Signs and symptoms of Lassa fever typically occur 1-3 weeks after the patient comes into contact with the virus. For the majority of Lassa fever virus infections (approximately 80%), symptoms are mild and are undiagnosed. Mild symptoms include slight fever, general malaise and weakness, and headache. In 20% of infected individuals, however, disease may progress to more serious symptoms including hemorrhaging (in gums, eyes, or nose, as examples), respiratory distress, repeated vomiting, facial swelling, pain in the chest, back, and abdomen, and shock. Neurological problems have also been described, including hearing loss, tremors, and encephalitis. Death may occur within two weeks after symptom onset due to multi-organ failure.
The most common complication of Lassa fever as deafness. Various degrees of deafness occur in approximately one-third of infections, and in many cases hearing loss is permanent. As far as is known, severity of the disease does not affect this complication: deafness may develop in mild as well as in severe cases.
Mode of transmission of Lassa fever
The reservoir, or host, of Lassa virus is a rodent known as the “multimammate rat” (Mastomysnatalensis). Once infected, this rodent is able to excrete virus in urine for an extended time period, maybe for the rest of its life. Mastomys rodents breed frequently, produce large numbers of offspring, and are numerous in the savannas and forests of west, central, and east Africa. In addition, Mastomys readily colonize human homes and areas where food is stored. All of these factors contribute to the relatively efficient spread of Lassa virus from infected rodents to humans
Transmission of Lassa virus to humans occurs most commonly through ingestion or inhalation. Mastomys rodents shed the virus in urine and droppings and direct contact with these materials, through touching soiled objects, eating contaminated food, or exposure to open cuts or sores, can lead to infection.
Because Mastomys rodents often live in and around homes and scavenge on leftover human food items or poorly stored food, direct contact transmission is common. Mastomys rodents are sometimes consumed as a food source and infection may occur when rodents are caught and prepared. Contact with the virus may also occur when a person inhales tiny particles in the air contaminated with infected rodent excretions. This aerosol or airborne transmission may occur during cleaning activities, such as sweeping.
Direct contact with infected rodents is not the only way in which people are infected; person-to-person transmission may occur after exposure to virus in the blood, tissue, secretions, or excretions of a Lassa virus-infected individual. Casual contact (including skin-to-skin contact without exchange of body fluids) does not spread Lassa virus.
Prevention of Lassa fever
Measures to prevent Lassa fever are:
- Primary transmission of the Lassa virus from its host to humans can be prevented by avoiding contact with Mastomys rodents, especially in the geographic regions where outbreaks occur.
- When caring for patients with Lassa fever, further transmission of the disease through person-to-person contact or nosocomial routes can be avoided by taking preventive precautions against contact with patient secretions (called VHF isolation precautions or barrier nursing methods).
- Further, educating people in high-risk areas about ways to decrease rodent populations in their homes will aid in the control and prevention of Lassa fever.
References
Adewuyi, G. M., Fowotade, A. &Adewuyi, B. T. (2016). Lassa fever: Another infectious menace. Afr J ClnExperMicrobiol. 10(3):144-155.
Arnold, R. B. & Gary, G.W. (1977).A neutralization test survey for Lassa fever activity in Lassa, Nigeria, Trans. Roy. Soc. Trop. Med. Hyg., 71, 152-154.
Bowen, M. D. (2009). Genetic diversity among Lassa virus strains.J Virol.74(15):6992-7004.
Carey, D. E. (1972).Lassa Fever Epidemiological aspect of the 1970 epidemic, Jos, Nigeria, Trans. Roy. Soc. Trop. Med. Hyg., 66, 402-408.
Centre for Disease Control and Prevention [CDC](2015). Fact sheet: Lassa fever. 2015. Retrieved on 4th November, 2016 from http://www.cdc.gov/vfh/lassa/pdf/factsheet.pdf.
Centre for Disease Control and Prevention [CDC] (2014). Lassa fever fact sheet. 2014. Retrieved on 4th November, 2016 from http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/factsheets/lassa_fever_fact_sheet.pdf.
Eze, K. C., Salami, T. A. T., Eze,I.C., Pogoson, A. E., Omordia, N. &Ugochukwu,M.O. (2010). High Lassa fever activity in Northern part of Edo state, Nigeria: re-analysis of confirmatory test results. Afr J Health Sci.17:52-56.
Federal Ministry of Health, Nigeria.(2016). What you need to know about Lassa fever. 2008; pp 4, 9.
Fichet-Calvet, E. & Rogers, D. J. (2009). Risk maps of Lassa fever in West Africa. PLoSNegl Trop Dis. 3:388.
