Lassa Fever

Lassa Fever overview and Definition

Lassa fever is an acute viral infection which occurs by the rat and it is most common among south Africa. This can be life threatening and it causes severe damage to the Liver, Spleen, Kidney and it can be fatal. The incubation time for Lassa fever might vary from six days to three weeks. Most people have mild or no symptoms. Some studies suggest that the incubation period varies from seven to 10 days and in some people, up to about 21 days.


It is common among the south African people.


Pathogenesis of the Lassa fever:

Host Cell Entry:

After transmission the Lassa virus first infects the endothelial cells. The Lassa virus gains the entry into the host cell by means of the cell surface receptor which is called as the alpha dystroglycan a versatile receptor of the proteins of extracellular matrix .

The lassa virus is an enveloped virus meaning which has the outer surface coating. Unlike other enveloped viruses which uses clathrin coated pits for cellular entry and bind to the receptors in the pH dependant fashion, Lassa virus enters the cell via endocytosis using the alpha dystroglycan receptor ( which is present everywhere and shows the expressed cell surface receptor) , independent of either clathrin, caveolin, dynamin or actin.

Unlike most enveloped viruses which use clathrin - coated pits for cellular entry and bind to their receptors in a pH dependent fashion, Lassa virus instead undergoes cellular entry via endocytosis using alpha-dystroglycan receptor (ubiquitously expressed cell surface receptor), independent of either clathrin, caveolin, dynamin or actin.

RNA Synthesis:

Intracellular RNA synthesis is initiated within an L-polymerase enzyme, which utilizes viral RNA templates and nucleocapsid protein NP to synthesize viral ribonucleoprotein (RNP). Once synthesized, RNP is transmitted to the host cell cytoplasm, and transcription of mRNA and antigenomic RNA (agRNA).

Host immune response:

After entering into the host immune system the production of the ribonucleoprotein which show exonuclease activity and causes the inhibition of the host type I IFN signaling.

which in turn cause platelet dysfunction, hepatic necrosis, suppression of cardiac function, and development of Lassa fever-associated clinical manifestations, including facial edema, pleural and pericardial effusions, and hypovolemic shock. These might result in the release of pro inflammatory cytokines. It affects all the organs but liver and auditory sensorineural system are involved.

When the the host immune system does not provides the proper immune response to control viral dissemination along with the disseminated replication in tissues and absence of neutralizing antibodies which might result in the death of the host.


Routes of Transmission

It commonly occurs when the person come into contact with the urine and other fecal materials of the rat. The rat that causes the disease is called as the Multimmate rat ( Mastomys natalensis)

Clinical signs & symptoms

 The symptoms include the damage to the vital organs such as the nervous system, cardiac system and pulmonary problems.


Symptoms can include:

bleeding in the gums, nose, eyes, or elsewhere

difficulty breathing

a cough

swollen airways

vomiting and diarrhea, both with blood

difficulty swallowing


swollen face

pain in the chest, back, and abdomen


hearing loss, which may be permanent

abnormal heart rhythms

high or low blood pressure

pericarditis, a swelling of the sac that surrounds the heart





Differential Diagnosis

Molecular methods:

Polymerase chain reaction (PCR) assays have been proven to be more sensitive than either LAT or culture tests, and highly specific. Countercurrent immunoelectrophoresis has been shown to be an effective research diagnostic method but has been largely supplanted by PCR.

Chest Xray:

The chest x ray predicts any abnormal area in the lungs

Computed tomography:

It reveals the slice of the lung. It uses both the combination of x ray and computer aided device.

It helps to analyse the size, shape and position of any lung tumour and also it helps in the detection of enlarged lymph nodes.

It also looks for any masses in the adrenal gland, liver, brain and other organs.

 CT guided needle Biopsy:

CT scan might be used to guide a biopsy needle into this  area to get the tissue for lung and further investigations are made.

MRI scan:

It uses the soft tissue image of the organ. It uses the both the magnet and radiowaves and aids in the view of soft tissues of the internal organs.

Immunosorbent assay- detect the  specific IgM or IgG antibodies.


Lumbar puncture or spinal tap:

 The fluid is drawn from the spinal cord and further investigations are made.


Normal erythrocyte sedimentation problems:

A normal erythrocyte sedimentation rate-  it is defined as the rate of red blood cell which are termed as erythrocytes and their deposition or sedimentation rate. 




Avoid exposure to the contacts with the contaminated urine and faecal materials of the rat

Prevent contamination of the food substances from the rodents

Wear  masks, gloves and proper clothing to prevent from the virus.

Avoid the entry of rodents inside the home

Wash the hands properly before and after the meals.