Lassa Fever Rages On in Nigeria

Mar 7, 2016 | Cheryl Lang, Tessa Runels, Colleen Nguyen | Outbreak News

Lassa fever is endemic to Nigeria, with annual spikes in disease incidence occurring between December and February (6). Since August 2015, there have been 175 reported cases and 101 deaths across Nigeria (9). In Nigeria, the four states being significantly affected by this disease are Bauchi, Edo, Oyo and Taraba (6). The ongoing outbreak is comparable in size to an outbreak in 2012, which resulted in 397 suspected cases, 87 confirmed cases and 40 deaths (12). In the wake of the current outbreak, and as a means of disease prevention, it is reported that Nigerians are stocking up on rat poison, although the Minister of Health promotes the use of traps instead (10,11). The WHO notes that extensive contact tracing is underway, with no contacts having contracted the disease as of January 25 (6).


All About Lassa Fever

Lassa fever is a zoonotic (or animal-borne) acute viral illness that is endemic to areas of West Africa (1). This illness was first discovered in 1969 and was named after the town in Nigeria where it was first identified and isolated (1). The disease is primary spread through contact with items contaminated with rodent feces. It is endemic among the rodent population in countries such as Nigeria, Sierra Leone, Guinea, and Liberia, where it is known to cause outbreaks on an almost annual basis (1, 6). Currently, Nigeria is experiencing an outbreak of Lassa fever and many states are struggling to halt the spread of the virus (6, 10).


Epidemiology of Lassa Fever

The natural host of Lassa fever is a rodent called the multimammate rat (2, 7, 8). This rodent is populous in the savannahs and forests of West Africa, but may also live in human homes and locations where food is stored (2). These rodents breed frequently and produce large numbers of offspring, making them perfect for spreading the virus efficiently (2). Once a rodent is infected with Lassa virus, it excretes the virus through urine and feces for an extended period of time—and sometimes even for the rest of its life (2). The virus can then be transmitted to humans through the inhalation or ingestion of dust particles containing the virus (2, 7). Due to proximity of the rodents to humans, the zoonotic transmission of the virus happens relatively frequently (2). The annual incidence of Lassa fever across this region is estimated to be as high as 300,000 cases, and 5,000 deaths (7).

Infection via contact often occurs after touching objects soiled with infected rodent excretions, eating contaminated food, and the virus entering the body through open cuts and wounds (2). Airborne transmission of the virus can occur during cleaning activities that disperse the viral particles into the air, such as sweeping the fecal matter of an infected rodent (2). 

Lassa virus can also be transmitted between humans when a person comes into contact with the blood, tissue, secretions, or excretions of another individual infected with the virus (2). It is important to note that Lassa virus is not transmitted through skin-to-skin contact and is only transmitted through the exchange of bodily fluids with an already-infected individual (2). Person-to-person transmission in endemic regions is common in healthcare settings, such as hospitals and clinics. This nosocomial spread of the virus can occur through contaminated medical equipment in resource-limited settings where proper infection-control techniques are not always practiced (2).


Signs, Symptoms, and Treatment

For approximately 80% of Lassa virus infections, symptoms are mild and frequently go undiagnosed (3). These mild febrile symptoms usually include a slight fever, general malaise, weakness, and headache (3). More serious symptoms, including hemorrhage, respiratory distress, vomiting, facial swelling, chest pain, back pain, abdomen pain, and shock, are experienced in the remaining 20% of infected individuals. Neurological issues, such as deafness, tremors, and encephalitis, have also been reported (3). Of these neurological complications, deafness is the most common and occurs in one-third of symptomatic infections (3). In many cases, the deafness is permanent (3).

Most symptoms do not appear until one to three weeks after initial exposure (3). For serious infections, death due to multi-organ failure can occur within two weeks after the onset of severe symptoms (3). Only 1% of all Lassa fever virus infections result in death, but the proportion of deaths is much higher among those hospitalized for Lassa fever (3,8). Historically, there have been outbreaks of Lassa fever where the case-fatality rates reached 50% in hospitalized patients (3).

The only available treatment for Lassa fever is ribavirin, an antiviral (4). It has been shown to be most effective when given to infected individuals early in the course of the illness and in conjunction with supportive care(8,4). There are currently no vaccines available to prevent Lassa fever (4).



In order to quell the spread of Lassa fever, it is advised that people engage in practices such as using rodent-proof containers to store food and keeping their homes clean to deter rodents (5). These practices, along with other easily implemented changes, can help prevent the zoonotic transmission of the virus. If individuals do become infected with the virus, efforts can be taken to prevent human-to-human transmission in hospital settings as well. These precautions include wearing protective equipment around infected individuals such as masks, gloves, gowns, and goggles and other sanitation techniques (5).

Lassa Fever can be easily prevented. Further precautions need to be taken in order to control the recent outbreak in Nigeria and prevent future outbreaks from occurring. By taking these precautions, Nigeria could help it from spreading to others and prevent more deaths caused by the virus.




1.    Center for Disease Control.  Lassa Fever. (2015). Retrieved March 01, 2016, from

2.      Center for Disease Control. Lassa Fever: Transmission. (2014). Retrieved March 01, 2016, from

3.      Center for Disease Control. Lassa Fever: Signs and Symptoms. (2014). Retrieved March 01, 2016, from

4.     Center for Disease Control. Lassa Fever: Treatment. (2014). Retrieved March 01, 2016, from

5.     Center for Disease Control. Lassa Fever: Prevention. (2014). Retrieved March 01, 2016, from

6. World Health Organization. Lassa Fever – Nigeria. (n.d.). Retrieved March 01, 2016, from

7. Lassa Fever. (n.d.). Retrieved March 01, 2016, from

8. Center for Disease Control. Lassa Fever Fact Sheet. (n.d.). Retrieved March 1, 2016, from

9.  Bhadelia, Nahid et al. “Zika isn’t the only outbreak. Nigeria struggles to rein in Lassa Fever”. NPR. Retrieved March 7, 2016, from

10.  NAN (n.d.). Preventing Lassa fever infection in Nigeria. The Guardian. Retrieved March 1, 2016, from

11.  Rat poison sales soar as Nigeria fears spread of Lassa fever. (2016, January 25). The Guardian. Retrieved March 1, 2016, from

12. Tomasulo, A. (n.d.). Lassa Fever Spreads Through Nigeria. HealthMap. Retrieved March 1, 2016, from

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