Lassa Hemorrhagic Fever (LHF) otherwise known as Lassa fever is an acute viral hemorrhagic fever caused by the Lassa virus. Lassa virus was first recognized in 1969, named after a small town Lassa, Borno State in North eastern Nigeria. Lassa fever is a member of the Arenaviridae virus family. Similar to Ebola, clinical cases of the disease had been known for over a decade, but had not been connected with a viral pathogen. Its natural host is the multimammate rat (Mastomys natalensis).This ubiquitous African rodent lives in close association with humans and is commonly found in and around houses in rural areas. Lassa virus can be transmitted when a human comes into contact with an infected rat’s feces, urine, or the bodily fluid of an infected human. Transmission through contaminated food is common, as the rats can excretes in food stores. While in some cases, the infection has no noticeable impact; it is, in other cases, fatal. The CDC estimates that in 20% of Lassa cases, patients suffer a severe multisystem disease, and the case –fatality rate has reached as high as 50% or even more. Lassa frequently infects people in West African. It results in 300,000 to 500,000 cases annually and causes about 5,000 deaths each year. Outbreaks of the disease have been observed also in Sierra Leone, Liberia and Guinea. These rats breed frequently and bear many offspring, increasing the potential for spread of the virus from rats to humans. Although the rodent reservoir exists across wide areas of Africa, Lassa virus appears to be restricted to the continent’s western part. Closely related viruses are found in other areas, but their potential for causing human disease is poorly understood.
SIGNS AND SYMPTOMS OF LASSA FEVER
Lassa virus is estimated to be responsible for about 5,000 deaths annually. The fever accounts for up to one-third of deaths in hospitals within the affected regions and 10-16% of total cases. Initial symptoms include:
- Sore throat
- Facial swelling
- Pains in the joint and lower back
- Headache and non productive cough commonly follow.
Diarrhea tend to seize at the end of the first week, whereas other gastrointestinal symptoms such as: abdominal pain, vomiting (bloody),Nausea, constipation, and dysphasia (difficulty swallowing) may persist into the second week of illness. Chest pain, often pleuritic in nature, increases in intensity during the first week and maybe present during the second and third weeks.
After the first week of illness, the patient begins recovery in milder case, but starts to deteriorate clinically in more serious ones. Dizziness, tinnitus, and unilateral or bilateral hearing loss are less frequent and later symptoms appearing during the second week of illness. Abnormal signs include conjunctiva inflammation, coated tongue, and exudative pharyngitis. Complications of Lassa fever include deafness, sensor neural deafness, shock, and hypotension. Some patients experience adult respiratory distress syndrome.
Clinical Lassa fever infections are difficult from other viral hemorrhagic fever such as Ebola and Marburg, and from more common febrile illness such as Malaria.
CAUSES AND RISK FACTORS FOR LASSA FEVER
Lassa virus is Zoonotic(transmitted from animals),in that it spreads to humans from rodents, specifically multimammate mice. The virus is shed in their excreta(urine and feces),which can be aerosolized. Infection in humans typically occurs by exposure to animal excrement through the respiratory or gastrointestinal tracts.
Inhalation of tiny particles of infectious material (aerosol) is believed to be the most significant means of exposure. It is possible to acquire the infection through broken skin or mucous membranes that are directly exposed to infectious material. Transmission from person to person has also been established, presenting a disease risk for health workers. Frequency of transmission by sexual contact has not been established. Individuals at risk are those who live or visit areas with a high population of Mastomys rodents infected with Lassa virus or are exposed to infected humans.
DIAGNOSIS OF LASSA FEVER
Establishing a clinical diagnosis at an early stage is especially important because of the transmissibility of infection from person to person and the need for effective isolation of the patient and for containment of potentially infectious specimens during virological and clinicopathological testing. Lassa fever maybe suspended on clinical grounds, but specific early diagnosis depends upon isolation of the virus. Virus isolation is best accomplished from serum obtained during the first 2 weeks of illness. Lassa fever is most diagnosed by using Enzyme-Linked Immunosorbent Serologic Assay (ELISA), which detect Immunoglobin M (IgM) antibodies as well as Lassa antigen. Test for antigen and IgM antibodies give 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 levels in the blood. The incubation period is generally between 7 and 10days,but maybe as short as 3days or as long as 17days.A prodome has not been defined, but the onset of illness is usually insidious rather than sudden. The acute phase has lasted 2-4 weeks in patients who have entered hospital, but is probably shorter in mild cases escaping medical attention.
PREVENTION OF LASSA FEVER
Prevention of Lassa virus infection requires an understanding of the disease and its mode of transmission. Control of the Mastomys rodent population is impractical, so measures are limited to keeping rodents out of homes and food supplies, as well as maintaining effective personal hygiene. Gloves, masks, laboratory coats, and goggles are advised while in contact with an infected person. These issues in many countries are monitored by a department of public health. In less developed countries, these types of organizations may not have the necessary means to effectively control outbreaks. There is no Vaccine to prevent Lassa fever in humans. To prevent Lassa fever, we must prevent its spread by rats.
TREATMENT OF LASSA FEVER
All persons suspected of Lassa fever infection should be admitted to isolation facilities, and their body fluids and excreta properly disposed of. Early and aggressive treatment using ribavirin was pioneered by Joe McCormick in 1979. After extensive testing, early administration was determined to be critical to success. Patients should also receive supportive care consisting of maintenance of appropriate fluid and electrolyte balance, oxygenation and blood pressure, circulatory volume, control of seizures, as well as treatment of any other complicating infections. Additionally, ribavirin is almost twice as effective as when given intravenously as when taken by mouth. Ribavirin is prodrug which appears to interfere with viral replication by inhibiting RNA-dependent nucleic acid synthesis, although the precise mechanism of action is disputed. The drug is relatively inexpensive, but the cost of the drug is still very high for many of those in West Africa States.
The basic ecology of Lassa fever appears to involve animal transmission of virus in Commensal populations of a single marine species Mastomys natalensis. Virus may spill over from the rodent cycle to man by various routes. Secondary spread between humans may occur within domiciliary groups, and persons infected within the community who develop clinical disease may introduce the virus into hospital and begin a cycle of Nosocomial infection. Recent evidence shows that avoiding direct contact with infected tissue, blood, secretions, and excretions, even in poorly equipped rural African hospitals, virtually eliminates the risk of infection. Lassa fever is characterized by high fever, sore throat, severe muscles, aches, skin rash with hemorrhages, headache, abdominal pain, vomiting and diarrhea. Approximately 15-20% of patients hospitalized for Lassa fever die from the illness. However, overall only about 1% of infection with Lassa virus results in death. Ribavirin antiviral drug has been shown to be most effective when given early in the course of the illness. Given its high rate of incidence, Lassa fever is a major problem in affected countries. To prevent Lassa fever, we must prevent its spread by rats.