Lassa Fever

What is Lassa fever?

The infectious disease known as Lassa Fever is caused by a virus that is native to West Africa. Lassa Fever was first diagnosed in 1969 when two nurses on mission in Nigeria died from it. The newly discovered Lassa Virus takes its name after the Nigerian town where the first diagnosis occurred. The Lassa Virus comes from the family of viruses called Arenaviridae. Carried by animals, it is a zoonotic RNA virus with a single strand.

In parts of West Africa where Lassa Fever is endemic, the disease is a considerable cause of mortality and morbidity. While approximately 80% of patients experience no symptoms or very mild symptoms, the remaining percentage develop a complex multisystem illness. When Lassa Fever is linked with an epidemic, the case fatality rate may rise to nearly 50%.

Lassa Fever is endemic to areas of West Africa. Cases have been reported in Nigeria, Guinea, Sierra Leone, and Liberia. As the virus is carried by various species of rodents throughout West Africa, Lassa Fever has a geographic range all throughout the region and potentially beyond.

It is estimated that there are anywhere between 100,000 to 300,000 individuals infected by the Lassa Virus each year. Approximately 5,000 of such cases result in death. These figures are not very reliable since Lassa Fever is neither regularly nor accurately surveyed in some parts of Africa. Parts of Liberia and Sierra Leone report that nearly 16% of the population in hospitals have Lassa Fever, which gives a crude picture of the severity of the disease in the region.

The reservoir of the Lassa Virus is the multimmammate rat from the genus Mastomys. At least two species of such rodents act as hosts to the virus in Sierra  Leone. The rodents reproduce very quickly and often, creating large populations that populate the forests and the savannas of East, Central, and West Africa. Mastomys rodents can colonize human establishments. Such factors make the transmission of the Lassa Virus to humans relatively easy.

Mastomys rodents excrete the virus in their droppings and urine. The virus is transmitted to humans when an individual comes in direct contact with the contaminated waste. Alternately, a person may touch objects or consume food that have been contaminated with rodent waste. The virus could also enter through open wounds or sores. Inhalation of the virus is possible when a person breathes in minute particles of contaminated air and is known as airborne or aerosol transmission. In some parts of Africa, Mastomys rodents are eaten as a food source so infection may happen when they are captured and prepared for consumption.

Transmission may occur from person to person when an individual makes contact with any tissue, blood, excretions or secretions of an infected person, but casual contact will not spread the virus. Nosocomial transmission can also occur with contaminated needles or other medical equipment.

The symptoms of Lassa Fever begin approximately one to three weeks after the initial infection. Symptoms may include pain in the chest wall, fever, back pain, abdominal pain, sore throat, conjunctivitis, swelling in the face, diarrhea, mucosal bleeding and proteinuria. There have been reports of neurological issues such as tremors, encephalitis, and hearing loss. The symptoms of Lassa Fever are so diverse that diagnosis can be challenging.

The diagnosis of Lassa Fever requires laboratory testing. Enzyme-linked immunosorbent serologic assays are used to find Lassa antigen as well as IgG and IgM antibodies. It takes about a week to culture the virus. In post-mortem examination, immunohistochemistry is used on tissue specimens. Reverse transcription-polymerase chain reaction can be used to detect the virus as well, but this method is typically reserved for research work rather than clinical.

Deafness is a standard complication of Lassa Fever and can occur in varying degrees in approximately a third of all cases. Permanent loss of hearing is typical and seems to have no correlation to the severity of the case. Another grave complication of Lassa Fever is sudden abortion.

Approximately 20% of hospitalized Lassa Fever patients die from the disease. Approximately one percent of infection cases without disease results in death. The death rate for Lassa Fever is especially high for pregnant women in their third trimester. Approximately 95% of unborn fetuses die if the mother is infected.

Treatment for Lassa Fever requires an antiviral medication called Ribavirin. Ribavirin is especially effective during the early stages of Lassa Fever. Supportive treatment such as maintaining blood pressure, oxygenation, and electrolyte and fluid levels is required for a full recovery. Any secondary infections that arise should be treated.

People living in areas with Mastomys rodents are at high risk. Medical care workers in such areas should take care to wear protective gear when treating any patient. Preventative measures include avoiding contact with rodents, keeping food in rodent-proof receptacles, and practicing excellent hygiene of the person and the household. Do not consume rodents; pest control and extermination is recommended. When nursing a person with Lassa Fever, wear protective clothing, gloves, and masks and take care not to come in contact with any bodily fluids. Practice proper equipment sterilization and keep infected individuals isolated from others until full recovery.