The Re- Emergence of the Dreadful Lassa Fever: Causes, Mode Of Transmission, Treatment And Prevention
By Fasoranti Afolabi
The Lassa virus was first described in 1950 and isolated in 1969 from blood samples belonging to two fatally ill nurses in Lassa (Nigeria). The zoonotic (animal-to-person transmission) Lassa virus is part of the Arenaviridae family and is polymorphic in shape, measuring between 80 and 300 nm in diameter. The lipid membrane of the virus particle contains two ring-shaped nucleocapsids (protein membranes), which contain the negative-sense RNA strands: L (long; approx. 7,400 bases) and S (short; approx. 3,400 bases). Like most RNA viruses, Lassa viral bacteria remain infectious for several hours at an ambient temperature. However, when heated to 60 °C for one hour, they become deactivated.
It probably exists in other parts of the continent too. So far, natural outbreaks of the disease have been described in the following countries: Sierra Leone, Côte d’Ivoire, Liberia, Guinea, Central African Republic and Nigeria. It is estimated that there are a total of 300,000 cases of Lassa fever per year, around 5,000 of which prove fatal. The last recorded large-scale outbreak of Lassa fever occurred between January 1996 and April 1997 in Sierra Leone. At that time, 823 people were infected, with 153 subsequently dying (19%). Then, in Summer 2000 a Dutch doctor became infected in Sierra Leone and died shortly after his return.
Nigeria has witnessed the upsurge of this diseases and currently ravaging the country. The Federal Ministry of Health gave the mortality rate to 41 deaths as at yesterday 13th January, 2016
The reservoir of the virus is wild rodents, particularly the African rat Mastomysnatalensis(multimammate rat) (asin, okete, ekutele, eku) and related species. Throughout their life infected rodents excrete the pathogen in very high concentrations and contaminate food and water. Smear infections may occur through broken skin and intact mucous membranes (airways) coming into direct contact with the bacterium. In some regions, the human population is known even to eat these infected rodents. Most cases of Lassa fever are reported during the dry season (January to March). Person-to-person transmission is possible in the first days after the infection through bleeding. Only a week after infection a high viremia (concentration of viruses in the blood) level is reached, through which other bodily fluids such as saliva and urine can also become infectious. Although the illness lasts between 1 and 4 weeks, viruses can be secreted in the urine 3 to 9 weeks after infection and up to 3 months in semen. Laboratory infections may occur due to the careless handling of the virus
It is difficult to diagnose Lassa fever exactly, as its symptoms are very similar to those of severe malaria, Ebola or even Yellow Fever. Where there are sufficient grounds to suspect infection, the first physician to treat the patient takes a blood sample, which is then analysed by special biosafety laboratories. . Infection is diagnosed by immunological tests, such as ELISA (enzyme-linked immunosorbent assay) and molecular tests, such as reverse transcription polymerise chain reaction (RT-PCR)
There is currently no vaccine against the Lassa viruses. However, research has been stepped up worldwide due to the bioterrorist threat. The aim is to develop a vaccine with attenuated (diluted) viruses, which could be combined with a Yellow Fever vaccine, since both illnesses are endemic in the same West African regions. The most recent vaccine trials with genetically modified VSV (vesicular stomatitis viruses) have produced encouraging results in non-human primates.
To date, the mortality rate falls when the antiviral drug and nucleoside analogue, Ribavirin, is administered 6 days from the appearance of the subjective symptoms. Therapy also generally involves intensive medical care. During this time, the patient is routinely monitored for the sudden onset of hypotension (drop in blood pressure).
Prevention and control
Prevention of primary transmission of the Lassa virusfrom its host to humans can be achieved by avoiding contact with Mastomys rodents, especially in the geographic regions where outbreaks occur. Puttingfood away in rodent-proof containers and keeping the home clean help to discourage rodents from entering homes. Using these rodents as a food source is not recommended. Trapping in and around homes canhelp reduce rodent populations. However, the wide distribution of Mastomysin Africa makes complete control of this rodent reservoir impractical. Lassa haemorrhagic fever is a highly virulent and contagious viral infection. Therefore, when caring for patients with Lassa fever, further transmission of the disease through person-to-person contact or nosocomial routes can be avoided by taking preventive precautions against contact with patient secretions by instituting strict barrier nursing. Such precautions
include wearing protective clothing, such as masks, gloves, gowns and goggles; using infection control measures, such as complete equipment sterilization and isolating infected patients from contact with unprotected persons until the disease has run its course. Body fluids, excreta and other materials that might have been contaminated should be handled carefully and disposed properly preferably by burning. All instruments used on the patient, if not disposable must be subjected to auto claving immediately. Absolute care should be taken when collecting pathological materials for laboratory investigations. Also correct procedure for transporting materials suspected to contain highly virulent virus or micro-organisms must be observed. Absolute precautionary measures must be taken while carrying out bacteriological and biochemical investigations in the blood and urine samples of suspected cases and such manipulations must be done in biosafety chambers. All those who had contact directly with suspected Lassahaemorrhagic fever patients have to be traced, monitored and specimens should be collected for laboratory diagnosis. Those who test positive have to be isolated and treated as soon as possible with ribavirin. Health education strategies for preventing infections in people living in endemic areas must be instituted and should focus on rodent control and minimizing contact with rodent excreta. Furthermore, emphasis should be placed on measures to control virus transmission from cases that include routine use of standard precautions, isolation of suspected cases and surveillance of contacts.
Lassa Fever is caused by a virus called Lassa Virus. The virus belongs to a group of viruses which cause hemorrhagic fevers such dengue fever, ebola fever, yellow fever etc. The virus is also characterised by bleeding disorders and can progress to shock and death in many cases.
HOW IT SPREADS
Lassa fever lives and multiplies in a particular type of rat called the Natal multimammate mouse which is found in sub-Saharan Africa.
The virus is contained in the urine and stool of rats. If the urine of the rats contaminates exposed food and humans the food, they can contract the disease. Breathing in the dried stool can also lead to being infected.
The virus spreads from person to person through direct contact with body fluids-saliva, nasal discharge, blood of infected persons etc.
THE SYMPTOMS YOU SHOULD KNOW ABOUT
Lassa Fever’s symptoms can be very tricky. It is usually similar to malaria and typhoid fever. These are some of the symptoms a victim experiences
- Sometimes vomiting and diarrhoea
- Yellowness of the eye balls.
- As the disease progresses, some organs may fail
- Bleeding may occur into the skin or/and from gums, nose, into the eyes.
- Organ failure.
- About 1% of all infections end up in death.
HOW TO PREVENT LASSA FEVER
Avoid Rats. Avoid contact with them, cover your food so they don’t come in contact with them. Do not eat rats
Isolate infected persons. And use of masks, gloves, gowns, goggles etc when attending to infected persons.
Keep a clean house and environment.
All persons suspected of Lassa fever infection should be admitted to isolation facilities and their body fluids and excreta properly disposed of. Early supportive care with rehydration and symptomatic treatment improves survival.
GENERAL DISEASES PREVENTION STRATEGIES IN CASE OF ANOTHER OUTBREAK OF EPIDEMICS
- Environmental and personal hygiene
- Food hygiene
- Public enlightenment and education should be constantly given to the general populace