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Lassa Fever: Transmission, Symptoms, Outbreak Update and Prevention

Lassa Fever:  Transmission, Symptoms, Outbreak Update and Prevention

Lassa fever is an animal-borne, or zoonotic, acute viral illness. It is endemic in parts of West Africa including Sierra Leone, Liberia, Guinea and Nigeria. Neighboring countries are also at risk, as the animal vector for Lassa virus, the “multimammate rat” (Mastomys natalensis) is distributed throughout the region.

The illness was discovered in 1969 and is named after the town called lassa in Borno state, Nigeria; where the first cases occurred.

An estimated 100,000 to 300,000 infections of Lassa fever occur annually, with approximately 5,000 deaths.

Transmission

The reservoir, or host, of Lassa virus is a rodent known as the “multimammate rat” (Mastomys natalensis). Once infected, this rodent is able to excrete virus in urine for an extended time period, maybe for the rest of its life.

Transmission of Lassa virus to humans occurs most commonly through ingestion or inhalation. Mastomys rodents shed the virus in urine and droppings and direct contact with these materials, through touching soiled objects, eating contaminated food, or exposure to open cuts or sores, can lead to infection.

Because Mastomys rodents often live in and around homes and scavenge on leftover human food items or poorly stored food, direct contact transmission is common. Mastomys rodents are sometimes consumed as a food source and infection may occur when rodents are caught and prepared. Contact with the virus may also occur when a person inhales tiny particles in the air contaminated with infected rodent excretions.

Direct contact with infected rodents is not the only way in which people are infected; person-to-person transmission may occur after exposure to virus in the blood, tissue, secretions, or excretions of a Lassa virus-infected individual.

Lassa virus may be spread in contaminated medical equipment, such as reused needles.

Signs and symptoms of Lassa fever

Signs and symptoms typically occur 1-3 weeks after the patient comes into contact with the virus. For the majority of Lassa fever virus infections (approximately 80%), symptoms are mild and are undiagnosed.

Mild symptoms include slight fever, general malaise and weakness, and headache. In 20% of infected individuals, however, disease may progress to more serious symptoms including hemorrhaging (in gums, eyes, or nose, as examples), respiratory distress, repeated vomiting, facial swelling, pain in the chest, back, and abdomen, and shock. Neurological problems have also been described, including hearing loss, tremors, and encephalitis.

Death may occur within two weeks after symptom onset due to multi-organ failure.

Outbreak Update in Nigeria

9 states have been affected so far which are: Ondo, Edo, Ebonyi, Taraba, Plateau, Bauchi, Ogun, Abia and Delta

-Total confirmed cases : 258

-Total Deaths; 41

-Health workers affected: 5

Prevention

  1. Primary transmission of the Lassa virus from its host to humans can be prevented by avoiding contact with Mastomysrodents, especially in the geographic regions where outbreaks occur.
  2. 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.
  3. Trapping in and around homes can help reduce rodent populations; however, the wide distribution of Mastomysin Africa makes complete control of this rodent reservoir impractical.
  4. When caring for patients with Lassa fever, further transmission of the disease through person-to-person contact or nosocomial routes can be avoided by taking preventive precautions against contact with patient secretions (called Barrier nursing methods). 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.
  5. Further, educating people in high-risk areas about ways to decrease rodent populations in their homes will aid in the control and prevention of Lassa fever. Other challenges include developing more rapid diagnostic tests and increasing the availability of the only known drug treatment, ribavirin. Research is presently under way to develop a vaccine for Lassa fever.

 

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