Overview :West Nile Virus
West Nile Virus (WNV) is a mosquito-borne, single-stranded RNA virus that has been making headlines in recent years due to its rapid spread and potential to cause serious illness.
West Nile virus, a continuously spreading mosquito-transmitted flavivirus, has emerged as a public health concern worldwide. The growing list of its genetic lineages around the globe with vast genetic plasticity and the capability to adapt to a variety of hosts in any existing local niche are serious concerns.
West Nile Virus can present with flu-like symptoms such as fever, headache, body aches, and fatigue, making it easy to misdiagnose or overlook. This lack of awareness can delay timely diagnosis and treatment, leading to more severe complications in some cases.
Spreading Activity of West Nile Virus
The clinical severity of WNV infection around the globe in humans, birds, and horses has increased. Although its circulation is well-documented in India since 1955, its recent emergence with epidemic potential causing severe encephalitis in Tamil Nadu (2015–2017) and Kerala (2019), indicates that adequate training needs to be provided to the clinicians for the differential diagnosis of suspected arbovirus infections, particularly in the hotspots, along with periodical monitoring of molecular epidemiology of the circulating virus lineages with regard to their origin, evolution, establishment, and dispersal within the country.
Background
West Nile virus is known to be active in India since the 1950s. The first serological evidence of its circulation was documented in 1955. Subsequently, its widespread activity was recorded in various states, including Tamil Nadu, Karnataka, Andhra Pradesh, Maharashtra, Gujarat, Madhya Pradesh, Odisha, and Rajasthan states. Although frequent incidences of Japanese encephalitis (JE) negative and WNV or WNV-like outbreaks among AES cases were observed in Kerala, India, during 1996–1997 without etiological confirmation, the widespread circulation of WNV in Kerala has been demonstrated time to time.
It is interesting to note that the majority of the WNV isolates recovered in India were predominantly from southern India, implying the well-established surveillance network, particularly for Japanese encephalitis (JE) in the paddy agroecosystem-dominated southern India. However, the recent reporting of its emergence in other parts of India, i.e., northeastern parts and West Bengal, suggesting its widespread distribution across the country and its potential emerging and expanding behavior in the Indian subcontinent.
The emergence of WNV has been shown during the investigation of a massive episode of suspected dengue and chikungunya outbreak in West Bengal, the eastern part of India, in 2012. Interestingly, WNV, recovered during this episode, had a high genetic homology (98%) with the Kerala strain belonging to Lineage 1a (WNV 1048813-KC601756.1) isolated in 2011, which was genetically homologous (98.62%) to a Russian strain (Ast01-182-DQ411030).
Causes
Environmental Condition
One of the main reasons for the increase in WNV cases in India is the favorable environmental conditions that support the breeding and proliferation of the mosquitoes that transmit the virus. Mosquitoes belonging to the Culex genus are the primary vectors for WNV, and these mosquitoes thrive in warm and humid climates. With India’s tropical climate providing the perfect breeding grounds for these mosquitoes, it comes as no surprise that the country has seen a surge in WNV cases in recent years.
Lack of Awareness
Another factor contributing to the rise of WNV in India is the lack of awareness and preparedness among the general population and healthcare providers.
Urbanization
The increasing urbanization and human encroachment into natural habitats are also playing a role in the spread of WNV in India. As humans continue to encroach upon forested areas, they come into closer contact with wildlife that may be carrying the virus. This increases the chances of spillover events, where the virus is transmitted from animals to humans through infected mosquitoes, further fueling the spread of WNV.
Climate Change
Climate change is another factor that is contributing to the spread of WNV in India. Rising temperatures and changing rainfall patterns create more favorable conditions for mosquito breeding, leading to an increase in their population. Additionally, warmer temperatures can also accelerate the replication and transmission of the virus within the mosquitoes, making them more efficient vectors for spreading WNV.
The impact of climate change on the population dynamics of West Nile viruses and vectors in introduction, maintenance and transmission has been documented. Generation of whole-genome sequence of the circulating strains in India is recommended. In addition, its envelope gene, NS3- or NS5-based information could assist in uncovering the genetic structure of the WNV population globally. Such data could immensely impact future vaccine development strategies.
Preventive Measures:
To combat the growing threat of WNV in India, it is essential for authorities to take proactive measures to control mosquito populations and educate the public about the risks associated with the virus. This includes implementing mosquito control programs, such as fogging and larviciding, in high-risk areas, as well as raising awareness about the importance of using insect repellents and wearing protective clothing to prevent mosquito bites.
Innovative surveillance approaches, such as RT-PCR, biosensors, and nanopore rapid sequencing, can eliminate the potential cross-reactivity by circulating flaviviruses. These could confirm WNV etiology and help in the better and timely implementation of effective control measures. Appropriate methodologies should be optimized to explore residential birds as a sentinel system for early identification and monitoring of WNV activity to implement the control strategy in a timely manner. Nevertheless, the “One Health” approach could be a promising holistic strategy; it is expected to render feasible, sustainable, and successful WNV prevention and control measures in the country.
Conclusion:
In conclusion, the rise of WNV in India is a cause for concern, as the country is facing the prospect of transitioning from having sporadic cases to experiencing a full-blown epidemic. It is imperative for authorities to take swift and decisive action to curb the spread of the virus and protect the health and well-being of the population. By implementing effective mosquito control measures, raising awareness about the risks of WNV, and improving healthcare provider education, India can mitigate the impact of this emerging public health threat and prevent it from reaching epidemic proportions.
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