Lassa fever was first discovered in Sierra Leone in the 1950s but the virus responsible for the disease was not identified until 1969 when two missionary nurses died in Nigeria and the cause of their illness was found to be Lassa virus, named after a town in Borno State (Lassa in the Yedseram River valley) where the first cases were isolated. Notable outbreaks thereafter were reported in 1974 in Zonkwa, Kaduna State and Onitsha, Anambra State; and in 1976 in Pankshin, Plateau State. In Edo State where the disease is now endemic, Lassa fever was first reported in Ihumudumu Community, Ekpoma in 1984 and the virus was said to have claimed the life of the whole family of four. In 1989, the epidemic occurred again at Ekpoma before shifting to the South East, with Aboh Mbaise, Owerri and Aba affected.An outbreak of the disease was again reported in Lafia, from December 1993 to February 1994, while in August 1994 a single case of the disease was also reported in Lagos of a patient from Ekpoma.

From 1989 till date, there have been reports indicating that cases of Lassa fever are seen annually between November and February in Ekpoma, Edo state.The rest of the recorded outbreaks nationwide include: Northern parts of Edo State including Ekpoma, Igarra, and Ibilo (2001 and 2004);Ebonyi  and Ogun States (2005); Edo, Plateau, Kogi, Benue, Ondo, Nasarawa, and Ebonyi (2007/2008); Edo, Nasarawa, Gombe, Kaduna, Plateau, Ondo,Lagos States  and FCT(2009); Kaduna, Kebbi, Plateau, Taraba, Edo, Kogi andOndo (2010).In 2011, there were 1,172 confirmed cases of the diseased with 50 deaths in the country. At the beginning of 2012, 623 suspected cases were reported with 70 deaths in 19 of the 36 States. While in 2013 some 1,656 cases of the disease with 112 deaths in 23 states of the federation were reported. Between January and February 2014, cases have been reported from Ebonyi and Oyo states with one patient from Ebonyi state, a pregnant woman,confirmed to have died of complications resulting from the disease.

Epidemics of Lassa fever have also been documented in other West African countries including Liberia, Sierra Leone, Guinea, Mali and Senegal.

The main cause of Lassa fever is the Lassa virus (an RNA virus), which is carried by a special species of rat known as Mastomysnatalensis recognized by the multiple breasts on its ventral surface and its relative hairless tail.  This species of rats lives around houses where they often feed and breed copiously. Once infected, the rats are infected for life and transmit the virus to their offspring. The two major modes of transmission of the virus are from the rodents to human (inhalation of aerosolized virus, ingestion of food material contaminated by rodent excrement and catching and preparing this rat as food) and from human to human (direct contact with blood, tissue secretion or excreta and inhalation of aerosolized virus). Frequency of transmission via sexual contact has however not been established. Lassa fever is a seasonal disease that is prevalent between January and April as a result of bush burning that forces rodents out of their habitats to take refuge in nearby houses.

About 300,000-500,000 cases occur annually in the endemic West African sub region, with approximately 5,000 deaths, 3,000 of which is said to occur in Nigeria alone, especially in the rural areas. Lassa fever has been found to account for 20% of maternal deaths in Nigeria and approximately 90% in the other West African sub region. This is a pointer to the fact that Lassa fever could be a significant but hidden cause of maternal deaths in several communities in Nigeria. The risk of death from Lassa fever in the third trimester is significantly higher than that in the first two trimesters and higher than that for non-pregnant women, but evacuation of the uterus can significantly improve the mother’s chance of survival.

In 80% of cases, the disease is inapparent, but in the remaining 20%, it takes a complicated course. After an incubation period of six to twenty-one days, an acute illness with multiorgan involvement develops. Non-specific symptoms include fever, facial swelling, and muscle fatigue, as well as conjunctivitis and mucosal bleeding (mouth, nose, rectum and/or vagina). The later stages could be characterized by shock, tremor, seizures disorientation, coma and deafness.From the onset of the disease, fatality could occur within 14 days.

There is a range of laboratory investigations that are performed to diagnose the disease and assess its course and complications. ELISA test for antigen and IgM antibodies gives 88% sensitivity and 90% specificity for the presence of the infection. Other laboratory findings in Lassa fever include lymphopenia (low white blood cell count), thrombocytopenia (low platelets), and elevated aspartate aminotransferase (AST) levels in the blood. Lassa fever can also be found in cerebrospinal fluid. Even though Lassa fever starts with fever, just like malaria and typhoid, it is always safe during diagnosis for Lassa fever to be considered in febrile conditions where body temperature goes above 38oC.

In West Africa, where Lassa is most prevalent, it is difficult for doctors to diagnose due to the absence of proper equipment to perform tests, such that a case of abdominal pain due to Lassa fever could be mistaken for other illnesses such as appendicitis and intussusception thereby delaying treatment.Fortunately two reference centers, Irrua Specialist Hospital, Edo State and College of Medicine, University of Lagos, are approved in Nigeria for confirmation of diagnoses made elsewhere. C:\Users\OBI\Documents\LASSA FEVER\LASSA 1.htm – cite_note-17

Currently there is an effective drug, ribavirin,which has been demonstrated to reduce fatality from 55% to 5%; however its effectiveness is dependent upon earlier diagnosis and commencement of treatment within the first week of onset of symptoms. There is no licensed vaccine or immunotherapy available for prevention or treatment;however, it is heartwarming to know that many patients who survived initial infection developed immunity against future attacks.

Fortunately Imo State has not recorded any cases since the Aboh Mbaise incidence in1989. With the resurgence of the infection in neighboring Ebonyi and Rivers States however, the freedom from Lassa enjoyed now in the state may be under a severe threat, considering, especially, the levels of environmental decay – a veritable breeding ground for the vectors, which has characterized Owerri and its environs since the inception of the present administration.

Curiously, very little has been done to enlighten the people about the dangers of Lassa fever, which could be avoided or minimized by simply keeping a clean and hygienic environment.

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Robert Obi, a member of the Virology Research Group and Doctoral Student, College of Medicine, University of Lagos, is a Lecturer at the Department of Microbiology, Federal University of Technology, Owerri.

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