LASSA FEVER: Symptoms, Prevention And Treatment By WHO

Lassa fever is an acute viral haemorrhagic illness of 1-4
weeks
duration that occurs in West Africa.
*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.
*Lassa fever is known to be endemic in Benin (where it
was diagnosed for the first time in November 2014),
Guinea, Liberia, Sierra Leone and parts of 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.
Background
Though first described in the 1950s, the virus causing
Lassa disease was not identified until 1969. The virus is
a single-stranded RNA virus belonging to the virus
family Arenaviridae .
About 80% of people who become infected with Lassa
virus have no symptoms. One in five infections result
in severe disease, where the virus affects several
organs such as the liver, spleen and kidneys.
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.” Mastomys rats infected with Lassa
virus do not become ill, but they can shed the virus in
their urine and faeces.
Because the clinical course of the disease is so
variable, detection of the disease in affected patients
has been difficult. However, when presence of the
disease is confirmed in a community, prompt isolation
of affected patients, good infection protection and
control practices
and rigorous contact tracing can stop outbreaks.
Symptoms of Lassa fever
The incubation period of Lassa fever ranges from 6-21
days. The onset of the disease, when it is symptomatic,
is usually gradual, starting with fever, general
weakness, and malaise. 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, Vag!na or
gastrointestinal tract and low blood pressure may
develop. Protein may be noted in the urine.
Shock,seizures, tremor, disorientation, and coma may
be seen in the later stages. Deafness occurs in 25% of
patients whosurvive the disease. In half of these cases,
hearing returns partially after 1-3 months. Transient
hair loss and gait disturbance may occur during
recovery.
Death usually occurs within 14 days of onset in fatal
ases. The disease is especially severe late in
pregnancy, with maternal death and/or fetal loss
occurring in greater than 80% of cases during the third
trimester.
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. S3xual transmission of Lassa virus has been
reported.
Lassa fever occurs in all age groups and both
S3xes.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 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; and
many other diseases that cause fever, including
malaria, shigellosis, typhoid fever and yellow fever.
Definitive diagnosis requires testing that is available
only in specialized 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:
*antibody enzyme-linked immunosorbent assay
(ELISA)
*antigen detection tests
*reverse transcriptase polymerase chain reaction
(RT-PCR) assay
*virus isolation by cell culture.
Treatment and vaccines
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 forLassa 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.
Because Mastomys are so abundant in endemic areas, it
is not possible to completely eliminate them from the
environment.
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 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.
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 fevershould 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:http://www.who.int/mediacentre/factsheets/f