Introduction
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.
According to Ogbu, Ajuluchukwu and Uneke (2016), it is a cause for concern that Lassa fever which got its name from the town of Lassa in Nigeria where it was first identified in 1969 has literarily remained a recurring issue in the country’s health equation. They added that it is surprising to read in the news once again that the disease that was thought by everyone to have disappeared resurged in Asaba again despite the assurance given by the minister of health early in a press briefing early this year; precisely in the month of January, 2016.
Adewuyi, Fowotade and Adewuyi (2016) stated that in other words, it is a cause for concern that the resurgence of Lassa Fever in Asaba dismissed the hope raised by the Honourable Minister through his press briefing as a result of the outbreak of Lassa Fever earlier in the year. Against the foregoing backdrop, it is obviously regrettable to realize the fact that despite the hope raised by the minister earlier in the year that Nigerians have to once again experienced another gory tale of its outbreak in Delta State.
Definition of Lassa fever
According to the Centre for Disease Prevention and Control [CDC] (2014), 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.
The World Health Organisation [WHO] (2015) stated that 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” (Mastomys natalensis) is distributed throughout the region. In 2009, the first case from Mali was reported in a traveller living in southern Mali; Ghana reported its first cases in late 2011. Isolated cases have also been reported in Côte d’Ivoire and Burkina Faso and there is serologic evidence of Lassa virus infection in Togo and Benin.
The number of Lassa virus infections per year in West Africa is estimated at 100,000 to 300,000, with approximately 5,000 deaths. Unfortunately, such estimates are crude, because surveillance for cases of the disease is not uniformly performed. In some areas of Sierra Leone and Liberia, it is known that 10%-16% of people admitted to hospitals every year have Lassa fever, which indicates the serious impact of the disease on the population of this region (WHO, 2015).
Historical background on Lassa fever
In the 1960’s Frame at Columbia University sought and received the collaboration of Rockefeller Foundation personnel, by now integrated into the faculty of Yale University School of Medicine, in screening the families of medical missionaries in Africa for indigenous viral infections. This cooperation resulted in the isolation of Lassa virus in 1969. The original virus strain was obtained from the blood of a missionary nurse from Jos, Nigeria. She was the fourth patient in a nosocomial transmission chain originating from an obstetrical patient residing in Lassa, Nigeria, who sought treatment in Jos for a septic abortion (Frame, 1970).
In 1970 another Lassa outbreak occurred in the hospital at Jos. There were 28 cases and 13 deaths. Ratttus Ratttus and Mus musculus were found in and near houses of patients but none yielded Lassa virus, and retrospective analysis of this epidemic revealed that transmission of infection had occurred directly in the hospital (Carey, 1972). Although gastro-intestinal hemorrhage similar to that characteristic of the South American arenaviral hemorrhagic fevers (SAHF) was observed in some patients, unique complications such as pleural effusion, deafness and acute “nephritis” were recorded (White, 1972).
In 1972 Lassa fever hospital “outbreaks” were recognized in Liberia and Sierra Leone (Monath, 1973). During investigation of the latter, several Lassa virus isolates were made from mastomys natalensis, a rodent found in man-disturbed biotopes and human dwellings throughout most of sub-Saharan Africa. A similar study in the region of Jos, Nigeria, employing a neutralization test which has not proven to be reproducible, showed that 13 percent of persons had Lassa virus antibodies (Arnold & Gray, 1977).
More recently a fluorescent antibody method has been employed to measure anti-Lassa antibodies. By this technique, Lassa virus has been documented to occur in humans in most of West Africa including Ivory Coast, Ghana, Senegal, Guinea, Gambia, Upper Volta, Mali and the Central African Empire (Frame, 1975).
But Mastomys rodents are present in much of Africa. Why is Lassa fever a West African disease? Although nature’s pattern is unclear, there are clues. A virus antigenically related, but probably not identical, to Lassa has been isolated from mastomys in Mozambique. Elucidation of its pathogenetic properties and geographic distribution may help unravel the mystery. In addition Mastomys natalensis rodents bearing three distinct numbers of chromosomes have been reported from Africa. West African animals have 32 and 38 chromosomes, while those in southern Africa have 32 or 36 chromosomes. The latter forms have been documented to be distinct biological species. Time and work will tell us whether these clues are relevant (Green, Gordon & Lyon, 1976).
Simple biological and virological parameters, however, suggest that the pathogenesis of Lassa virus infection in man is distinct from that of Junin and Machupo viruses. The South American diseases are characterized by a bleeding diathesis, low and intermittent viremia and a long interval between onset of symptoms and appearance of humoral antibodies. Virus is rarely detectable in urine and other clinical complications are unusual. Lassa fever, in contrast, is marked by prolonged viremia, a variety of major clinical manifestations and the simultaneous presence of both virus and specific antibodies in the blood during the second week of illness (Monath, 1974).
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 (Federal Ministry of Health, 2008).
Omilabu, Badaru, Okokhare, Drosten and Emmerich (2013) identified 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.
Approximately 15%-20% of patients hospitalized for Lassa fever die from the illness. However, only 1% of all Lassa virus infections result in death. The death rates for women in the third trimester of pregnancy are particularly high. Spontaneous abortion is a serious complication of infection with an estimated 95% mortality in fetuses of infected pregnant mothers. Because the symptoms of Lassa fever are so varied and nonspecific, clinical diagnosis is often difficult. Lassa fever is also associated with occasional epidemics, during which the case-fatality rate can reach 50% in hospitalized patients (CDC, 2015).
Mode of transmission of Lassa fever
The reservoir, or host, of Lassa virus is a rodent known as the “multimammate rat” (Mastomys natalensis). 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 (Eze, Salami, Eze, Pogoson, Omordia & Ugochukwu, 2010).
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 (Fichet-Calvet & Rogers, 2009).
In the opinion of Bowen (2009), 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. Person-to-person transmission is common in health care settings (called nosocomial transmission) where proper personal protective equipment (PPE) is not available or not used. Lassa virus may be spread in contaminated medical equipment, such as reused needles (Omilabu et al., 2013).
Prevention of Lassa fever
Measures to prevent Lassa fever as stated by CDC (2015) 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. Putting food away in rodent-proof containers and keeping the home clean help to discourage rodents from entering homes. Using these rodents as a food source is not recommended. Trapping in and around homes can help reduce rodent populations; however, the wide distribution of Mastomys in Africa makes complete control of this rodent reservoir impractical.
- 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). Such precautions include wearing protective clothing, such as masks, gloves, gowns, and goggles; using infection control measures, such as complete equipment sterilization; and isolating infected patients from contact with unprotected persons until the disease has run its course.
- 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.
Conclusion
In conclusion, the resurgence of Lassa fever in Nigeria can be controlled effectively by adopting proper standard precautions in hospitals as well as communities. Educating the public on the mode of transmission of this virus and the need for proper hygiene and environmental sanitation should be emphasized.
Recommendations
Having critically reviewed the resurgence of Lassa fever in Nigeria the following is recommended:
- The general public should be educated on the causes of Lassa fever and measures to prevent it.
- Measures should be put in place to kill the Mastomys rat which is referred to as the major carrier of Lassa fever.
- Awareness campaign should be carried out by government, community leaders and other stakeholders on Lassa fever to keep the general public informed.
- The mass/social media should be used to sensitized the people on measures to prevent the disease.
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