LASSA FEVER

LASSA FEVER

INTRODUCTION

Lassa fever, also known as Lassa hemorrhagic fever (LHF), is a type of viral hemorrhagic fever caused by the Lassa virus. Many of those infected by the virus do not develop symptoms. When symptoms occur they typically include fever, weakness, headaches, vomiting, and muscle pains. Less commonly there may be bleeding from the mouth or gastrointestinal tract. The risk of death once infected is about one percent and frequently occurs within two weeks of the onset of symptoms. Among those who survive about a quarter have hearing loss, which improves over time in about half.

The disease is usually initially spread to people via contact with the urine or feces of an infected multimammate rat. Spread can then occur via direct contact between people.

DIAGNOSIS

Confirmation is by laboratory testing to detect the virus's RNA, antibodies for the virus, or the virus itself in cell culture. Other conditions that may present similarly include Ebola, malaria, typhoid fever, and yellow fever. The Lassa virus is a member of the Arenaviridae family of viruses. 

INCUBATION PERIOD ( 6 -21 DAYS)

After an incubation period of six to 21 days, an acute illness with multiorgan involvement develops. 

PREVENTION

There is no vaccine.Prevention requires isolating those who are infected and decreasing contact with the rats.Other efforts to control the spread of disease include having a cat to hunt vermin, and storing food in sealed containers.Treatment is directed at addressing dehydration and improving symptoms.The antiviral medication ribavirin may be useful when given early. These measures improve outcomes.

INCIDENCE

Descriptions of the disease date from the 1950s. The virus was first described in 1969 from a case in the town of Lassa, in Borno State, Nigeria. Lassa fever is relatively common in West Africa including the countries of Nigeria, Liberia, Sierra Leone, Guinea, and Ghana. There are about 300,000 to 500,000 cases which result in 5,000 deaths a year.

SIGNS AND SYMPTOMS

In 80% of cases, the disease is asymptomatic, but in the remaining 20%, it takes a complicated course. The 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 to 16% of total cases.

Gastrointestinal tract ,NauseaVomiting (bloody), Diarrhea (bloody), Abdominal pain, Constipation, difficulty swallowing, Hepatitis, Cardiovascular system ,Pericarditis,Hypertension,Low blood pressureFast heart rate,Respiratory tract ,Cough,Chest pain,Shortness of breath,Pharyngitis,Pleurisy,Nervous system ,Encephalitis,Meningitis, Unilateral or bilateral hearing loss, observed in up to one third of adults, which becomes permanent in two thirds,Epileptic seizure.  Mastomys natalensis, the natural reservoir of the Lassa fever virus 

CAUSATIVE ORGANISMS

Lassa virus commonly spreads to humans from other animals, specifically the natal multimammate rat or African rat, also called the natal multimammate mouse (Mastomys natalensis). This is probably the most common mouse in equatorial Africa, common in human households and eaten as a delicacy in some areas.

Individuals who are at a higher risk of contracting the infection are those who live in rural areas where Mastromys are discovered, and where sanitation is not prevalent. Infection typically occurs by direct or indirect 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 been established, presenting a disease risk for healthcare workers. The virus is present in urine for between three and nine weeks after infection, and it can be transmitted in semen for up to three months after becoming infected.

Control of the Mastomys rodent population is impractical, so measures focus on keeping rodents out of homes and food supplies, encouraging effective personal hygiene, storing grain and other foodstuffs in rodent-proof containers, and disposing of garbage far from the home to help sustain clean households. Gloves, masks, laboratory coats, and goggles are advised while in contact with an infected person, to avoid contact with blood and body fluids. 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. 

TREATMENT

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.

When Lassa fever infects pregnant women late in their third trimester, inducing delivery is necessary for the mother to have a good chance of survival.This is because the virus has an affinity for the placenta and other highly vascular tissues. The fetus has only a one in ten chance of survival no matter what course of action is taken; hence, the focus is always on saving the life of the mother.Following delivery, women should receive the same treatment as other Lassa fever patients. 

PROGNOSIS

 About 15–20% of hospitalized Lassa fever patients will die from the illness. The overall mortality rate is estimated to be 1%, but during epidemics, mortality can climb as high as 50%. 

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