.
*TRANSMISSION*
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.
This aerosol or airborne transmission may occur during cleaning activities, such as sweeping.
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.
Casual contact *(including skin-to-skin contact without exchange of body fluids)* does not spread Lassa virus.
Person-to-person transmission is common in health care settings (called nosocomial transmission) where proper personal protective equipment *(PPE)* is not available or not used. Lassa virus may be spread in contaminated medical equipment, such as reused needles.
*SIGNS & SYMPTOMS*
Signs and symptoms of Lassa fever 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.
The most common complication of Lassa fever is *deafness*. Various degrees of deafness occur in approximately *one-third of infections, and in many cases hearing loss is permanent.*
As far as is known, severity of the disease does not affect this complication: deafness may develop in mild as well as in severe cases.
*Approximately 15%-20% of patients hospitalized for Lassa fever die from the illness.*
The death rates for women in the *third trimester of pregnancy are particularly high.
* Spontaneous abortion is a serious complication of infection with an estimated 95% mortality in fetuses of infected pregnant mothers.
Because the *symptoms of Lassa fever are so varied and nonspecific, clinical diagnosis is often difficult.
* Lassa fever is also associated with occasional epidemics, during which the case-fatality rate can reach 50% in hospitalized patients.
*RISK OF EXPOSURE*
Individuals at greatest risk of Lassa virus infection are those who live in or visit endemic regions, *including Sierra Leone, Liberia, Guinea, and Nigeria* and have exposure to the multimammate rat.
Risk of exposure may also exist in other west African countries where *Mastomys rodents exist.*
*Hospital staff are not at great risk for infection as long as protective measures and proper sterilization methods are used.*
*PREVENTION*
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. Trapping in and around homes can help reduce rodent populations.
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.
*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. Patients should also receive supportive care consisting of maintenance of appropriate fluid and electrolyte balance, oxygenation and blood pressure, as well as treatment of any other complicating infections.
*REMEMBER:* Prevention is better than cure.
*….Your Health, Our Concern*