What is Lassa Fever?
Lassa fever is an acute hemorrhagic viral illness caused by the Lassa virus, a single-stranded RNA virus belonging to the virus family Arenaviridae, first described in the 1950s but finally identified only in 1969 in Lassa town, Nigeria. The disease is known to be endemic in Benin, Guinea, Liberia, Sierra Leone and parts of Nigeria, but probably exists in other West African countries as well.
The Lassa virus is transmitted to humans via contact with food or household items contaminated with rodent urine or faeces. Person-to-person infections and laboratory transmission can also occur, particularly in hospitals lacking adequate infection prevent and control measures.It is estimated that Lassa feveraffects between 100,000 to 300,000 patients in West Africa per year, with approximately 5,000 deaths.In about 80% of people who become infected with Lassa virus, symptoms are mild and are usually undiagnosed. One in fiveinfections result in severe disease,
where the virus affects several organs such as the liver, spleen and kidneys.
The overall case fatality rate is about 1%. Observed case fatality rate among patients hospitalized with severe cases of Lassa fever approaches 15%.
How is it possible to catch Lassa Virus?
Lassa fever is a zoonotic disease; the virus is found in a rodent known as the multimammate rat, which, once infected, is able to excrete virus in the urine for an extended time period, maybe for the rest of its life. In addition to the numerous amount in wild environment, this rodent is known to colonize human homes and areas where food is stored, spreading the infection. Infected rats with Lassa do not become sick, but they can shed the virus in their urine and feces, and direct contact with these materials, through touching soiled objects, eating contaminated food, or exposure to open cuts or sores, can lead to infection.
The virus is transmitted mainly by ingestion or inhalation through the following modalities:
1) To be in contact with infected rat’s urine or faeces;
2) Eating food contaminated with rat’s excreta or contaminated rats
3) Inhalation of air (i.e., aerosols) contaminated with rodent excretion (e.g. during sweeping in or around houses infested with contaminated rats)
4) Person-to-person transmission is common in health care settings, where proper personal protective equipment (PPE) is not available or not used. The infection may be spread through contaminated medical equipment, such as reused needles.
Casual contact (including skin-to-skin contact without exchange of body fluids) does not spread Lassa virus
What are the symptoms of Lassa fever disease?
Signs and symptoms of Lassa fever typically occur after an incubation period of 1-3 weeks after the infection. For the majority of Lassa fever virus infections (approximately 80%), symptoms are mild and develop gradually, including: fever, general malaise and weakness, and headache. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough, and abdominal pain may follow.
In severe cases, facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract, and low blood pressure may develop. Proteins may be noted in the urine. Shock, seizures, tremor, disorientation, and coma may be seen in the later stages.
Death usually occurs within 14 days after onset in fatal cases. The disease is especially severe late in pregnancy, with maternal death and/or fetal loss occurring in greater than 80% of the cases during the third trimester.
Deafness occurs in 25% of patients who survive to the disease. In half of these cases, hearing returns partially after 13 months. Transient hair loss and gait disturbance may occur during recovery.
How to diagnose Lassa Fever?
Clinical diagnosis of the disease is difficult due to varied and non–specific symptoms, which may be confused with those of other diseases (e.g. malaria, typhoid fever, yellow fever), especially early in the course of the disease. It is also difficult to proceed with a differential diagnosis from other viral haemorragic fevers such as Ebola
Definitive diagnosis requires tests that are available only in specialized laboratories. Laboratory specimens should be handled with care, as they may be hazardous.
Definitive tests to diagnose Lassa Fever are:
antibody enzyme-linked immunosorbent assay (ELISA)
antigen detection tests
reverse transcriptase polymerase chain reaction (RT-PCR) assay
virus isolation by cell culture.
Treatment and immunization:
Ribavirin, an anti-viral drug, seems to be partially effective in the treatment of Lassa fever, especially when given early in the course of the illness. Supportive care is normally required, including fluids and electrolyte balance, oxygen supply, and treatment of any other complicating infections
Currently, there is no available vaccine that protects against Lassa fever
How to prevent it?
First line of protection is related to the improvement of housekeeping and strong application of general and food related hygienic measures. Is also important to apply barriers aimed to discourage and prevent rodents from entering houses. Effective measures include storing grain and other foodstuffs in rodent-proof containers, disposing of garbage far from the house, maintaining clean households, and keeping cats.
Because Mastomys rats are so abundant in endemic areas, it is not possible to eliminate them from the environment. Additional preventive measures include:
1) Avoid eating food of unknown origin
2) Avoid going into places with stored wheat or millet seeds
3) Avoid eating “bush suya”
4) Normal hygiene measures, including frequent hand washing
5) Trapping in and around homes
6) Family members who are caring sick persons should be careful to avoid contact with blood and body fluids.
7) Asking immediately for medical advice in case of suspicion of Lassa Fever infection
8) In healthcare settings, staff should always apply standard infection prevention and control precautions when caring for patients, regardless of their presumed diagnosis. These include basic hand hygiene, respiratory hygiene, use of personal protective equipment (to avoid contamination with splashes or other contact with infected materials), safe injection practices, and safe burial practices.
9) Moreover, in medical environments, it is fundamental to perform complete equipment sterilization, and to isolate infected patients, preventing contact with unprotected persons until the disease has run its course.
Things to Remember:
The most important thing is to maintain a good hygienic condition, to store the food in adequate stores, and to keep the rats away. Family members and health care personnel should always be careful to avoid contact with blood and body fluids while caring for sick persons. Routine barrier nursing precautions probably protect against transmission of Lassa virus in most circumstances.