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Rift valley fever is a viral zoonosis caused by Rift Valley Fever Virus (RVFV) that belongs to Bunyaviridae of Arbovirus kind. Many areas in the world, particularly in Africa have been suffering from health and economic burden as a direct result of the Rift Valley fever. Nonetheless, searching for effective ways for prevention of universal RVFV outbreak is at an alarming rate. The following is a brief discussion on causes of this fever, its symptoms as well as possible ways of prevention.
RVFV is a virus, a member of phlebovirus genus in Bunyaviridae family , transmitted by a mosquito. The virus has a single stranded RNA genome of negative or ambi-sense polarity, which composes of three segments: small (S), medium (M), and large (L). The (S) segment expresses nucleocapsid (N) and nonstructural (NSs) proteins. The (M) segment encodes viral glycoproteins [ Gn & Gc ] in a single open reading frame (ORF) , which is projected from the viral surface, and aids virus in attaching and entering the host cell , as well as nonstructural proteins ( NSm1 , NSm2 ). Meanwhile, ( L) segment expresses RNA dependent - RNA polymerase ( L-protein ) , which is important for viral RNA replication & mRNA synthesis. NSs is a virulence factor and IFN-Î² antagonist; so that , it evades innate anti-viral host response , whereas , the role of NSm in the virulence as suppressor of virus- induced apoptosis . [1,2,4]
RVFV is serious threat to many parts of the world especially in Africa, for both human and animal health. It leads to longstanding morbidity and mortality in susceptible patients. RVFV is dangerous for infected human who constantly have suffered febrile illness , headache , articular pain , malaise , photophobia ,retinal degeneration ( that may result in blindness) and fulminate hepatitis[1,4]. It also causes hemorrhagic fever and meningo - encephalitis. For animals, the story is not better. The infected animals could be characterized by fever , hepatitis and high abortion rate.[1,7]
As mentioned earlier, the major cause of fever is RVFV transmitted either by a mosquito's bite, aerosol released from infected animals, or close contact with the blood of slaughtered infected animals. . Therefore, development of more effective methods for prevention of RVFV outbreaks is a global health priority. This might be achieved by eradication of outbreaks, human disease determinants, transmission factors, rapid diagnosis of RVFV infection, and development of RVFV vaccines.
How do we eradicate outbreak?
One way that maintains RVFV in nature is by transmission of mosquitoes in flood water. After heavy rainfall, many swamps are formed in different parts of the earth, where the mosquitoes live. Accurate climate prediction would be a possible way to provid the public with early warning about RVFV outbreak. Doing so, it would increase the probability of RVF prevention [ 1,3 ]
What is about RVFV diagnosis?
Like most viruses, the diagnosis of RVFV may be done by viral isolation ,antigen detection and specific antibody detection. However, these techniques aren't accurate and lengthy. Therefore, for protecting human and animal population, other more rapid, accurate and safer diagnostic tests should be applied on the free international trade of animals and animal products. These tests include RCR assays, which include reverse transcription (RT)-RCR , real time-PCR and real time reverse - transcription loop - mediated isothermal amplification ( RT-LAMP ) . The most recent and preferred assay is RT-LAMP owing to the fact that it is sensitive and specific, it can be assessed by unaided eye, and it can be done in one step and single tube reactions that are faster and less expensive . [1,3 ]
RVFV vaccination and therapeutics :
It is necessary to produce and discover new RVFV vaccines for the following reasons: the expansion of affected regions by the RVFV, including parts of Middle East; some of infected humans with RVFV die as a result of hemorrhagic symptoms; a broad range of mosquito species are involved in spreading of RVFV; and specific and effective therapies for RVFV are currently unavailable. In fact, there are several RVFV vaccines designed to elicit humeral immunity; but, these vaccines do not induce rapid protective neutralizing antibodies against lethal challenge, and many of these vaccines may not be suitable for human use. For instance, in the past, RVFV vaccines studies focused on inactivated and live - attenuated virus vaccines that elicit long-term protection. However, potential disadvantages may limit the wide spread use of live - attenuated vaccines which are teratogenic, abortion and reversion. In contrast, inactivated virus vaccines require multiple closes to maintain protection.[1,5,7]
Therefore, finding out more safe and effective RVFV vaccines remains the priority of all to protect humans and animals, as well. The ideal RVFV vaccines must be safe and highly effective, and has the ability to elicit rapid protective neutralizing antibodies and provide long - lasting protective immunity. [3,4] .To design vaccine with these properties, DNA vaccines have been developed based on DNA plasmids and alphavirus replicon vectors. DNA plasmid expresses the RVFV Gn glycoprotein coupled to C3d, which use as a molecular adjuvant for enhancing responses against irritant RVFV infection, whereas the alphavirue replicon vectors express Gc & Gn glycoproteins as well as the NSm protein; so that replicon vector- based vaccine induce protection antibody responses & provide 100% protection against lethal RVFV challenge which is proved demonstrated experimentally on mice . [4,5,6,7]
RVFV is still spreading among animal and human in sub- Saharan Africa and parts of middle East through epidemics and epizootics . Recent information about maintenance , pathogenesis and transmission of RVFV may give researchers a choice for developing more effective vaccine to help prevent RVF . All countries must work together and unite their efforts to face this serious fever caused by a disastrous virus. Otherwise, threat of death will be more closer to everyone, wherever he/ she lives.