What is Lassa Fever?
Lassa fever belongs to a group of viral hemorrhagic fevers and is also termed as Lassa hemorrhagic fever (LHF). The cause is the Lassa virus; hence the name "Lassa Fever." Many patients usually do not experience any symptoms and if they do develop them, they include weakness, fever, headaches, muscle pains and vomiting. Patient can also have bleeding from the gastrointestinal tract or mouth; however, this is not common. The mortality rate is about 1% with this infection and usually occurs within a couple of weeks after the development of the symptoms. About 25% of patients who survive Lassa fever will suffer from deafness, which gradually improves somewhat.
Lassa fever spreads to human beings through contact with the feces or urine of an infected multimammate rat. After this Lassa fever can directly spread through direct contact between human beings. It is difficult to come to a diagnosis of Lassa fever based on the symptoms alone as there are other similar conditions such as malaria, Ebola fever, yellow fever and typhoid fever. The diagnosis of Lassa fever can be confirmed by performing lab investigations, which detect the RNA of the Lassa virus, the virus itself or antibodies to the virus in cell culture.
There is no vaccine for Lassa fever. This condition can be prevented by isolating the infected patients and preventing contact with the rats. This can be done by adopting a cat to hunt the rats and keeping the food stored in sealed containers. Treatment of Lassa fever consists of addressing the patient's dehydration and trying to alleviate the symptoms. Antiviral medications, such as ribavirin is beneficial when given in early stages. All these things will help with improving the prognosis.
Causes of Lassa Fever
Mastomys natalensis is the rodent host of the Lassa fever virus. The Lassa virus gets transmitted to humans from Mastomys natalensis which is a natal multimammate mouse. The Lassa virus gets transmitted to human beings through contact with the urine or feces of the infected animals when they are accessing grains in the house. Exposure to animal excrement through the gastrointestinal tracts or respiratory tract is the common modality through which the infection gets transmitted. When people inhale tiny particles of this infectious material, then the person gets infected. This is thought to be one of the significant methods of exposure. Infection can also develop through contact via broken skin or mucous membranes, which get directly exposed to the infectious material. The infection can also gets transmitted from one person to another as the virus can still be found in the urine for around 4 to 9 weeks after infection, and is present in semen for around three months after the infection has occurred.
Signs & Symptoms of Lassa Fever
In majority of the patients, Lassa fever is asymptomatic; however, the remaining minority of the patients can experience a complicated course of this disease. Lassa fever is responsible for around 1/3 deaths in hospitals in affected regions. The incubation period is about six to 21 days, after which the patient experiences acute illness followed by involvement of multiple organs of the body. There are nonspecific symptoms, such as fever, muscle fatigue, facial swelling, mucosal bleeding and conjunctivitis. Other symptoms occurring as a result of the organs getting involved are:
Cardiovascular System Symptoms of Lassa Fever: Hypertension, pericarditis, tachycardia and hypotension.
The virus gets excreted in the patient's urine for about 4-9 weeks and in semen for around three months.
Diagnosis of Lassa Fever
It is difficult to differentiate Lassa fever from other viral hemorrhagic fevers such as Marburg and Ebola and from common fevers such as malaria. Laboratory investigations, such as ELISA test for antigen and IgM antibodies are performed for diagnosis of Lassa fever. Other test findings, which are seen in Lassa fever include lymphopenia (decreased white blood cell count), thrombocytopenia (decreased platelets), and increased aspartate aminotransferase blood levels. The Lassa virus is also found in the cerebrospinal fluid.
Treatment for Prevention of Lassa Fever
It is important to start early and aggressive treatment using the antiviral medicine, ribavirin, for effective treatment. Other than this, ribavirin is more effective when it is given intravenously than orally. Other than ribavirin, treatment consists of fighting hypotension, fluid replacement, and blood transfusion. Other than this intravenous interferon therapy can also be used.
If a pregnant woman gets infected with Lassa fever in the third trimester, then it is recommended to induce delivery for a chance of survival. The Lassa virus has an affinity for highly vascular tissues such as placenta. The unborn fetus has about 1 in 10 chance of survival irrespective of the course of action taken; because of which the main aim is saving the life of the mother. After the delivery, the mother should continue to receive the same treatment as that of other patients suffering from Lassa fever.
Prevention of Lassa Fever
The population of the rodents can be difficult to control, so instead measures are taken to prevent the rodents from accessing the food supplies and entering the homes along with maintaining good personal hygiene, such as using masks, gloves, goggles and lab coats when in contact with an infected person. Patients who are suspected to have Lassa fever infection must be admitted to isolation accommodations along with proper disposal of the body fluids and excreta. Research is going on to find a vaccine for Lassa virus.
Prognosis of Lassa Fever
The mortality rate of Lassa fever is around 1%, but it can get as high as 50% during an epidemic. Around 15-20% the patients who are hospitalized due to Lassa fever will die from this infection. The mortality rate increases to more than 80% if pregnant women get infected in their third trimester with death of the fetus also occurring in almost all those cases. Abortion in such cases cuts the risk of mother's death. Some patients who survive can have permanent effects from Lassa fever, such as partial or complete deafness. Treatment with ribavirin has helped in cutting down the fatality rates of Lassa fever.