Lassa fever is an acute viral hemorrhagic fever caused by the Lassa virus. It was first discovered 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.
The infection is endemic in West African countries, resulting in 300,000–500,000 cases annually, causing approximately 5,000 deaths.
Outbreaks of the disease have been observed in Nigeria, Liberia, Sierra Leone, Guinea, and the Central African Republic, but it is believed that human infections also exist in Democratic Republic of the Congo, Mali, and Senegal.
The primary animal host of the Lassa virus is the Natal Multimammate Mouse (Mastomys natalensis), an animal indigenous to 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 has become a major problem in the African region.
Lassa virus is zoonotic (transmitted from animals), in that it spreads to humans from rodents, specifically multi-mammate rats (Mastomys natalensis).
This is probably the most common rodent in equatorial Africa, ubiquitous in human households and eaten as a delicacy in some areas.
In these rats infection is in a persistent asymptomatic state. The virus is shed in their excreta (urine and feces), which can be aerosolized. In piemel 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 infective 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 infective material.
Transmission from person to person has also been established, presenting a disease risk for healthcare workers. Frequency of transmission via sexual contact has not been established.
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.
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. The other symptoms arising from the affected organs are:
The virus is excreted in urine for three to nine weeks and in semen for three months.
Early and aggressive treatment using Ribavirin was pioneered by Joe McCormick in 1979. After extensive testing, it was determined that early administration is 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, it is necessary to induce delivery 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 focus is always on saving the life of the mother. Following delivery, women should receive the same treatment as other Lassa fever patients.
SIGA Technologies is developing an antiviral drug that has been shown effective in treating experimentally infected guinea pigs.
In a study conducted at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), treatment with ST-193 once a day for 14 days resulted in significant reduction in mortality (71% of the animals survived at the low dose), whereas all untreated animals and those treated with ribavirin died within 20 days of the infection.
Due to threat of disease being used as a potential military weapon, a vaccine to reverse the disease is still being worked on.
As serious as the disease is, there are numerous accounts of survival. However, there have been lasting effects of the disease.
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.
The infection is endemic in West African countries, resulting in 300,000–500,000 cases annually, causing approximately 5,000 deaths.
Outbreaks of the disease have been observed in Nigeria, Liberia, Sierra Leone, Guinea, and the Central African Republic, but it is believed that human infections also exist in Democratic Republic of the Congo, Mali, and Senegal.
The primary animal host of the Lassa virus is the Natal Multimammate Mouse (Mastomys natalensis), an animal indigenous to 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 has become a major problem in the African region.
Lassa virus is zoonotic (transmitted from animals), in that it spreads to humans from rodents, specifically multi-mammate rats (Mastomys natalensis).
This is probably the most common rodent in equatorial Africa, ubiquitous in human households and eaten as a delicacy in some areas.
In these rats infection is in a persistent asymptomatic state. The virus is shed in their excreta (urine and feces), which can be aerosolized. In piemel 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 infective 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 infective material.
Transmission from person to person has also been established, presenting a disease risk for healthcare workers. Frequency of transmission via 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.
Symptoms
In 80% of cases, the disease is asymptomatic, but in the remaining 20%, it takes a complicated course. It is estimated that the virus is 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.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. 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
The virus is excreted in urine for three to nine weeks and in semen for three months.
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, it was determined that early administration is 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, it is necessary to induce delivery 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 focus is always on saving the life of the mother. Following delivery, women should receive the same treatment as other Lassa fever patients.
SIGA Technologies is developing an antiviral drug that has been shown effective in treating experimentally infected guinea pigs.
In a study conducted at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), treatment with ST-193 once a day for 14 days resulted in significant reduction in mortality (71% of the animals survived at the low dose), whereas all untreated animals and those treated with ribavirin died within 20 days of the infection.
Due to threat of disease being used as a potential military weapon, a vaccine to reverse the disease is still being worked on.
As serious as the disease is, there are numerous accounts of survival. However, there have been lasting effects of the disease.
