Awareness Of Lassa Fever And Its Vector Control Measures Among Ekpoma Market Women

INTRODUCTION

Lassa fever is an acute viral zoonotic illness caused by Lassa virus, an arena virus known to be responsible for a severe haemorrhagic fever characterized by fever, muscle aches, sore throat, nausea, vomiting, and chest and abdominal pain1. Lassa virus is an enveloped, single-stranded, bisegmented RNA virus belonging to the Arenaviridae family. Like other arenaviruses, Lassa virus lacks a conventional negative-strand coding arrangement and the isolates of the virus differ in their genetic, serologic, and pathogenic characteristics1. Lassa virus is spherical in shape and measures between 70 and 150 nm in diameter. It has a smooth surface envelope with T-shaped spikes measuring 7–10nm and built with glycoprotein. The envelope encloses the genome which has helical nucleocapsid measuring between 400 and 1300 nm in length [1]. Often the interior contains electron dense granule identified as the host cell ribosome from where the name “arena” was derived meaning sandy. Lassa virus can be inactivated in ultraviolet, gamma irradiation, heating from 56–100oC and pH range between 5.5 and 8.5. Chemical agents like 0.5% sodium hypocorite, 0.5% phenol and 10% formalin are good inactivants against the virus 1.

The single-stranded arena virus genome consists of a small (s) and a large (l) RNA fragment, sizes 3.4 and 7 kb, respectively and the sRNA encodes the viral glycoprotein precursor protein (GPC) and the nucleoprotein (NP), while the lRNA encodes the viral polymerase and a small, zinc-binding (Z) protein1. New methods for full-length sRNA amplification are facilitating research efforts on the identification and molecular analysis of new arena viruses or arena virus strains 1. The sequencing of Lassa virus sRNA has enabled the identification and molecular characterisation of four Lassa virus strains. These include: the strain Josiah, originating from Sierra Leone, the strain Nigeria and strain LP 1,

both from Nigeria, and the strain AV imported into Germany by a traveller who had visited Ghana, Côte D?Ivoire, and Burkina Faso. Sequencing of sRNA of Lassa virus indicated a considerable genetic variation among the strains of the virus, however, phylogenetically, strain AV appears to be closely related to strain Josiah from  Sierra Leone [1]. The virus exhibit persistent, asymptomatic infection, with profuse urinary virus excretion in Mastomys natalensis, the ubiquitous and highly commensal rodent host 2.

On acquisition of the virus through contact with urine, saliva, respiratory secretion and blood, Lassa fever infection is initiated in the victim. Lassa fever is a generalised infection with haemorrhagic dissemination of the virus to multiple organs and systems via the blood stream, lymph vessels, respiratory tract, and/or digestive tract 3.

The incubation period of Lassa haemorrhagic fever is between 3 and 21 days.

Clinical presentation includes an insidious fever, headache, rigors, myalgia, backache and malaise. The body temperature may increase to 40oC, and often evening body temperature is higher than that of morning. Constant fever for 10 days or more is an indication of higher level of intoxication which triggers of weakness, muscle pains, abortion and mental disorder. [1] Other signs are nausea, vomiting, abdominal and pleuritic pain, as well as pain around hepatic area. Specific features in various systems of infected person are prominent.

In the

oral cavity, ulcerated lesions with white or yellow exudates are present in the faucets, soft plates and tonsil and bleeding from the gums. Other features include sore throat that can cause dysphasia, pharyngitis and watery diarrhoea which can lead to dehydration. The liver and kidney are often inflamed, enlarged and painful on palpitation 1.

Diagnosis is by laboratory detection of Lassa antigen, antibodies or by viral isolation technique. Deferential diagnosis includes Ebola haemorrhagic fever, malaria, diphtheria, typhoid fever, legionella, yellow fever, Congo hemorrhagic fever, etc 1.

Ribavirin is the choice of antivirus drug most effective in treatment. Supportive treatment is often necessary and includes fluid replacement, blood transfusion, administration of paracetamol, phylometadione, ringer lactate, haemocoel quinine and broad spectrum antibiotics 1.

Lassa fever is endemic in West Africa and has been reported from Sierra Leone, Guinea, Liberia, and Nigeria 1.

In 1972 Lassa virus was isolated for the first time from a non-human source, the pooled heart, lung, spleen, and kidney of each of 10 Mastomys natalensis collected in Eastern Province, Sierra Leone 4. To date, no other natural nonhuman host has been identified 4.

The Natal Multimammate Mouse (Mastomys natalensis) is a species of rodent in the family Muridae. It is also known as the Natal Multimammate Rat, the Common African Rat, or the African Soft-furred Rat 5.

Its natural habitats are subtropical or tropical dry forests, subtropical or tropical moist lowland forests, dry savannah, moist savannah, subtropical or tropical dry shrub land, subtropical or tropical moist shrub land, arable land, pastureland, rural gardens, urban areas, irrigated land, and seasonally flooded agricultural land 5. Though Mastomys natalensis is one of the most widely distributed and abundant rodents in Africa, it is however completely absent only from very arid regions, such as the Namib and Kalahari deserts 5.

Mastomys natalensis is of small to moderate size, ±10-15 cm in body length with a tail of approximately the same size. The colour of the pelage varies considerably with the age of the animal and has also been noted to vary according to the terrain in which specimens are caught. The colour on the dorsal side may be grey to greyish brown, brown or reddish buff, but it is lighter on the ventral side 5. This numbers from 8 to 12 pairs, which are continuously distributed from the pectoral to the inguinal region 5.

Mastomysis natalensis has an outstanding prolific reproductive capacity. A mean litter size of (6.6 – 8.5) young has been established by some workers 5. Breeding is especially favoured by the availability of an abundant food supply. While breeding tends to take place throughout the year, a marked increase occurs during the latter part of the rainy season when ripening of grass and other seeds takes place5.

Mastomysis natalensis is a clean animal, both as concerns its own body and with regard to its nest5. Although it is inoffensive and lives in peaceful coexistence with its own rodent species, it shows a certain amount of aggression towards man. It is a relatively difficult animal to handle in the laboratory because of its tendency to bite5.

Infected rodents remain carriers throughout their life and do not show clinical symptoms but excrete the virus through the urine, saliva, respiratory secretion and exposed blood vessels through micro or macro trauma2.

Since certain varieties of Mastomys often live in human homes, the Lassa virus is easily transmitted to humans. Transmission occurs via direct contact with rat urine, faeces, and saliva; via contact with excretion- or secretion-infected materials; or via ingestion of excretion-contaminated food. Victims can also become infected via skin breaks, via mucous membranes from aerosol transmission from dust-borne particles1.

In some areas, the rodents are used as a food source, thus providing additional exposure to the infected rat blood, as well as allowing ingestion of potentially contaminated meat. Laboratory workers become infected usually from contact with rodent saliva6. Almost invariably, Mastomysis natalensis urinates when frightened and contaminates the hands of the person handling it. In view of the known persistence of the Lassa virus in urine, this tendency may play a role in the transmission of the disease to man5.

Historically, Lassa fever was first described in Sierra Leone in the 1950s but the virus responsible for the disease was not identified until 1969 when two missionaries nurses

died in Nigeria, West Africa, and the cause of their illness was said to be Lassa virus, named after the town in Nigeria (Lassa in Yedseram River valley) where the first cases were isolated2.

Since then, a number of outbreaks of Lassa virus infection were reported in various parts of Nigeria including Jos, Onitsha, Zonkuma, Abo-Mbaise, Owerri, Lafiya and Ekpoma in Edo state2 Epidemics have also been documented in other West African countries including Liberia, Sierra Leon, Guinea, Mali, and Senegal and a few case of the importation of Lassa into other part of the world have been reported2.

It is the most commonly “exported” hemorrhagic fever, it s victim carry the disease from Africa to the United States, to the United Kingdom, to the Netherlands, Israel and Japan. As at July 14 2010, Eight cases have been imported into the UK since 1980. All cases have derived from either Sierra Leone or Nigeria, except for a single case in February 2009 which had been acquired in Mali. World-wide, imported cases are very rare and occur almost exclusively in persons with high risk occupations such as medical or other aid workers. The risk to tourists is considered to be very low7.