LASSA FEVER

What is Lassa fever?

Lassa fever is an acute blood borne disease commonly found in West Africa. This disease is named after the village in Nigeria where it was first discovered in 1969. Lassa fever is known to be endemic in Guinea (Conakry), Liberia, Sierra Leone and parts of Nigeria, but probably exists in other West African countries as well. The disease occurs more often in the dry season, rather than in the rainy season.  There have been reports of over 40 deaths in 12 states of Nigeria within the last year alone.

Mode of infection

 A person can become infected by eating food contaminated with rat excreta, urine or saliva deposited on surfaces such as floors, beds, household utensils or in food and water e.g. surfaces of canned drinks/foods and other stored food items. Person to person infection also occurs through direct contact or inhalation of infected body fluids including blood, urine, saliva, throat secretion, etc. This is the reason why health care workers are also at a high risk of infection.

Signs and symptoms

The onset of the disease is usually gradual, starting with a fever, general weakness, and malaise.

After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain may follow.

Severe cases may progress to show facial swelling, fluid in the lungs, bleeding from the mouth, nose, vagina or gastrointestinal tract, and low blood pressure.

Seizures, tremor, disorientation, and coma may be seen in the late stages.

Deafness occurs in 25% of patients of whom half recover some function after 1-3 months.

Transient hair loss and gait disturbance may occur during recovery.

Animal reservoir

Lassa fever is a zoonotic disease, meaning that humans become infected from contact with infected animals. The animal reservoir, or host, of Lassa virus is a rodent of the genus Mastomys, commonly known as the “multimammate rat.” This rat can be difficult to identify. Mastomys infected with Lassa virus do not become ill, but they can shed the virus in their saliva and excreta (urine and faeces).

Who is at risk?

Lassa fever occurs in all age groups and in both men and women. Persons at greatest risk are those living in rural areas where these rats are usually found, especially in areas of poor sanitation or crowded living conditions. Health care workers are at risk if proper barrier nursing and infection control practices are not maintained.

How is Lassa fever transmitted?

Humans usually become infected with Lassa virus from exposure to excreta of infected rats. Both direct exposure, (touching the excreta) and Lassa virus may also be spread between humans through direct contact with the blood, urine, faeces, or other bodily secretions of a person with Lassa fever. There is no epidemiological evidence supporting airborne spread between humans. Person-to-person transmission occurs in both community and health care settings, where the virus may be spread by contaminated medical equipment, such as re-used needles. Sexual transmission of Lassa virus has been reported.

Diagnosis

Because the symptoms of Lassa fever are so varied and non-specific, clinical diagnosis is often difficult, especially early in the course of the disease. Lassa fever is difficult to distinguish from many other diseases which cause fever, including malaria, shigellosis, typhoid fever, yellow fever and other viral blood borne fevers.

Definitive diagnosis requires testing that is available only in highly specialized laboratories. Laboratory specimens may be hazardous and must be handled with extreme care. Lassa fever is diagnosed by detection of Lassa antigen, anti-Lassa antibodies, or virus isolation techniques.

Treatment and prophylaxis

The antiviral drug ribavirin is effective treatment for Lassa fever if given early on in the course of clinical illness.

Prevention

Effective preventive measures include:

·         Storing grain and other foodstuffs in rodent-proof containers,

·         Disposing of garbage far from the home,

·         Maintaining clean households

·         Washing the surfaces of canned foods and drinks before consumption of content.

·         Rinsing and cooking all foods thoroughly.

·         Regular fumigation of our homes and offices.

·         Keeping cats.

Because these rats are so abundant in endemic areas, it is not possible to completely eliminate them from the environment.

As always PREVENTION IS BETTER THAN CURE.

Dr. Olukayode Williams