Lassa fever or Lassa hemorrhagic fever ( LHF ) is an acute viral hemorrhagic fever caused by the Lassa virus and first described in 1969 in the town of Lassa, in Borno State , 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.
Lassa frequently infects people in West Africa. 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 in Nigeria , Liberia , Sierra Leone , Guinea , and the Central African Republic. The primary animal host of the Lassa virus is the Natal
multimammate mouse ( Mastomys natalensis), an animal found in most of sub-Saharan Africa. [ The virus is probably transmitted by contact with the feces or urine of animals accessing grain stores in residences. Given
its high rate of incidence, Lassa fever is a major problem in affected countries.
Signs and symptoms
Nonspecific symptoms include fever,
facial swelling, and muscle fatigue, as well as conjunctivitis and mucosal bleeding. The other symptoms arising from the affected organs
are:
Gastrointestinal tract
Nausea
Vomiting (bloody)
Diarrhea (bloody)
Stomach ache
Constipation
Dysphagia (difficulty swallowing)
Hepatitis
Cardiovascular system
Pericarditis
Hypertension
Hypotension
Tachycardia (abnormally high heart rate)
Respiratory tract
Cough
Chest pain
Dyspnoea
Pharyngitis
Pleuritis
Nervous system
Encephalitis
Meningitis
Unilateral or bilateral hearing deficit
Seizures
Clinically, Lassa fever infections are difficult to distinguish from other viral hemorrhagic fevers such as Ebola and Marburg, and from more common febrile illnesses such as malaria .
The virus is excreted in urine for 3-9 weeks and in semen for three months.
Causes
Lassa virus is zoonotic (transmitted from animals), in that it spreads to humans from rodents, specifically multimammate mice ( Mastomys natalensis). This is probably the
most common mouse in equatorial Africa, ubiquitous in human households and eaten as a delicacy in some areas. In these rodents, infection is in a persistent asymptomatic state.
The virus is shed in their excreta (urine and feces), which can be aerosolized. In fatal cases, Lassa fever is characterized by impaired or delayed cellular immunity leading to fulminant viremia .
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 healthcare workers. Frequency of transmission by sexual contact has not been established.
Prevention
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.
Researchers at the USAMRIID facility, where military biologists study infectious diseases, have a promising vaccine candidate. They have developed a replication -competent vaccine against Lassa virus based on recombinant vesicular stomatitis virus vectors expressing the Lassa virus glycoprotein. After a single intramuscular injection, test primates have survived lethal challenge, while showing no clinical symptoms.
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 McCormick in 1979.
After extensive testing, early administration was determined to be critical to success.
Additionally, ribavirin is almost twice as
effective when given intravenously as when taken by mouth. Ribavirin is a 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 African states. Fluid replacement, blood transfusion, and fighting hypotension are usually required.
Intravenous interferon therapy has also been used.
When Lassa fever infects pregnant women late in their third trimester, induction of 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.
Work on a vaccine is continuing, with multiple approaches showing positive results in animal trials.
