With the threat of Lassa fever bearing down on us, reminiscent of the Ebola virus disease, it becomes imperative to know as much about it as possible.
Reproduced in this article are the most important facts about Lassa fever as presented by the Centres for Disease Control and Prevention (CDC), the leading American public institute for health.
What is Lassa fever?
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, West Africa. The cause of the illness was found to be Lassa virus, named after the town in Nigeria where the first cases originated. The virus, a member of the virus family Arenaviridae, is a single-stranded RNA virus and is zoonotic (meaning spread by animals)
Where is Lassa fever found?
Lassa fever is an endemic disease in portions of West Africa. It is recognized in Guinea, Liberia, Sierra Leone, as well as Nigeria. However, because the rodent species which carry the virus are found throughout West Africa, the actual geographic range of the disease may extend to other countries in the region.
In what animal host is Lassa virus maintained?
The reservoir, or host, of Lassa virus is a rodent known as the multimammate rat of the genus Mastomys. It is not certain which species of Mastomys are associated with Lassa; however, at least two species carry the virus in Sierra
Leone.
Mastomys rodents breed very frequently, produce large numbers of offspring, and are numerous in the savannas and forests of West, Central, and East Africa. In addition, Mastomys generally readily colonize human homes. All these factors together contribute to the relatively efficient spread of Lassa virus from infected rodents to humans.
How do humans get Lassa fever?
There are a number of ways in which the virus may be transmitted, or spread, to humans.
- Mastomys rodents shed the virus in urine and droppings. Therefore, the virus can be transmitted through direct contact with these materials, through touching objects or eating food contaminated with these materials, or through cuts or sores.
- Because Mastomys rodents often live in and around homes and scavenge on human food remains or poorly stored food, transmission of this sort is common. Contact with the virus also may occur when a person inhales tiny particles in the air contaminated with rodent excretions. This is called aerosol or airborne transmission.
- Mastomys rodents are sometimes consumed as a food source, infection may occur via direct contact when they are caught and prepared for food
- Lassa fever may also spread through person-to-person contact. This type of transmission occurs when a person comes into contact with virus in the blood, tissue, secretions,or excretions of an individual infected with the Lassa virus.
- The virus CANNOT be spread through casual contact (including skin-to-skin contact without exchange of body fluids). Person-to-person transmission may also be spread through contaminated medical equipment, such as reused needles (this is called nosocomial transmission).
What are the symptoms of Lassa fever?
Signs and symptoms of Lassa fever typically occur 1-3 weeks after the patient comes into contact with the virus.
- These include fever, pain behind the chest wall, sore throat, back pain, cough, abdominal pain, vomiting, diarrhea, conjunctivitis, facial swelling, protein in the urine, and mucosal bleeding.
- Neurological problems have also been described, including hearing loss, tremors, and encephalitis.
- Because the symptoms of Lassa fever are so varied and nonspecific, clinical diagnosis is often difficult.
Are there complications after recovery?
- The most common complication of Lassa fever is deafness. Various degrees of deafness occur, and in many cases hearing loss is permanent. Deafness may develop in mild as well as in severe cases.
- Spontaneous abortion is another serious complication.
How is Lassa fever treated?
Ribavirin, an antiviral drug, has been used with success in Lassa fever patients. It has been shown to be most effective when given early in the course of the illness.
Who are at risk of getting the illness?
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. Hospital staff are not at great risk for infection as long as protective
measures are taken.
How is Lassa fever prevented?
- 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.
- Traps 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 can be avoided by taking preventive precautions against contact with patient secretions. 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.
