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, vagina 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 who survive 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 cases. 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. 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
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 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. 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 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.

Interesting

There's is a permanent vaccine for this right