- Lassa fever also known as Lassa hemorrhagic fever (LHF), is a type of viral hemorrhagic fever caused by the Lassa
virus.
- Many of those
infected by the virus do not develop symptoms, but when symptoms occur they
typically include fever,
weakness, headaches, vomiting, and muscle
pains. Less commonly there may be bleeding
from the mouth or gastrointestinal tract.
- The risk of
death once infected is about one percent (1%) and frequently occurs within two
weeks of the onset of symptoms.
- Among those who
survive about a quarter have deafness
which improves over time in about half.
- 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 prevention and control measures.
- Lassa fever is known to be
endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria, but
probably exists in other West African countries as well.
- The overall case-fatality rate is
1%. Observed case-fatality rate among patients hospitalized with severe cases
of Lassa fever is 15%.
- Early supportive care with
rehydration and symptomatic treatment improves survival.
Transmission
Humans usually become infected with Lassa virus
from exposure to urine or faeces of infected Mastomys rats.
Lassa virus may also be spread between humans
through direct contact with the blood, urine, faeces, or other bodily
secretions of a person infected 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.
Lassa fever occurs in all age groups and both
sexes. Persons at greatest risk are those living in rural areas where Mastomys
are usually found, especially in communities with poor sanitation or crowded
living conditions.
Health workers are at risk if caring for Lassa
fever patients in the absence of proper barrier nursing and infection
prevention and control practices.
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 other
viral haemorrhagic fevers such as Ebola virus disease as well as other diseases
that cause fever, including malaria, shigellosis, typhoid fever and yellow
fever.
Definitive diagnosis requires testing that is
available only in reference laboratories. Laboratory specimens may be hazardous
and must be handled with extreme care. Lassa virus infections can only be
diagnosed definitively in the laboratory using the following tests:
- reverse
transcriptase polymerase chain reaction (RT-PCR) assay
- antibody
enzyme-linked immunosorbent assay (ELISA)
- antigen
detection tests
- virus
isolation by cell culture.
Treatment and prophylaxis
The antiviral drug ribavirin seems to be an
effective treatment for Lassa fever if given early on in the course of clinical
illness.
There is no evidence to support the role of
ribavirin as post-exposure prophylactic treatment for Lassa fever.
There is currently no vaccine that protects against
Lassa fever.
Prevention and control
Prevention of Lassa fever relies on promoting good
“community hygiene” to discourage rodents from entering homes.
Effective measures include storing grain and other
foodstuffs in rodent-proof containers, disposing of garbage far from the home,
maintaining clean households and keeping cats.
Family members should always be careful to avoid
contact with blood and body fluids while caring for sick persons.
In health-care 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 block splashes or other
contact with infected materials), safe injection practices and safe burial
practices.
Health-care workers caring for patients with
suspected or confirmed Lassa fever should apply extra infection control
measures to prevent contact with the patient’s blood and body fluids and
contaminated surfaces or materials such as clothing and bedding.
When in close contact (within 1 metre) of patients
with Lassa fever, health-care workers should wear face protection (a face
shield or a medical mask and goggles), a clean, non-sterile long-sleeved gown,
and gloves (sterile gloves for some procedures).
Laboratory workers are also at risk. Samples taken
from humans and animals for investigation of Lassa virus infection should be
handled by trained staff and processed in suitably equipped laboratories under
maximum biological containment conditions.
On rare occasions, travellers from areas where
Lassa fever is endemic export the disease to other countries. Although malaria,
typhoid fever, and many other tropical infections are much more common, the
diagnosis of Lassa fever should be considered in febrile patients returning
from West Africa, especially if they have had exposures in rural areas or
hospitals in countries where Lassa fever is known to be endemic.
Health-care workers seeing a patient suspected to
have Lassa fever should immediately contact local and national experts for
advice and to arrange for laboratory testing.
Source: World
Health Organization (WHO)
Labels: Educative Article
