• Thursday, Nov 14, 2019
  • Last Update : 11:48 am

Dengue declining, West Nile virus on the way

  • Published at 01:24 am October 1st, 2019
WEB_Culex Mosquito
Culex Mosquito Wikimedia Commons

Breeding season of the Culex mosquito, which carries the West Nile virus, begins in October

The dengue outbreak this year affected thousands of people. Government data reports at least 87,000 people have been treated so far. Yet, even as the dengue season is coming to a close, another threat appears to be on its way to Bangladesh.

For the first time in Bangladesh, a person has been diagnosed with the West Nile virus, a mosquito-transmitted disease that is spreading across the globe.

In Europe, there have been 375 cases of the West Nile virus between January 1 and September 26 this year, with 35 deaths. In the same time period, there were 543 cases in the United States, with 25 casualtie. In 2018, Europe saw 1,503 cases with 180 deaths and the United States had 2,647 cases with 167 fatalities. It seems that in Europe the virus impact and fatalities from it, are declining.

How does the West Nile Virus spread?

The Culex mosquito carries the West Nile virus, while the Aedes mosquito carries the dengue virus. According to experts, the Culex breeding season begins in October and 80% of all mosquitos in Dhaka are of the Culex genus.  With the capital still combating a dengue outbreak, a fresh onslaught from a virus hitherto unencountered could prove to be devastating.

Prof Sanya Tahmina, director (Disease Control) at the Directorate General of Health Service (DGHS), says the case was originally identified by the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) which asked the Institute of Epidemiology, Disease Control and Research (IEDCR) for help. The DGHS was engaged in the process.

Dr Meerjady Sabrina Flora, director at IEDCR, said: “We have found the virus in migratory birds in our country. No local birds have been identified as carriers.”

The West Nile virus is carried by birds who pass it on to Culex mosquitoes, that in turn spread it among humans or birds.

Why is the Culex an imminent threat?

While the Culex mosquito breeds year round, it hits peak season between November and February. Of the three sub-species of Culex in Dhaka, Culex Quinquefasciatus is the most known carrier of the virus and is more prevalent in the capital.

Dr Kabirul Bashar, an entomologist with the Department of Zoology at Jahangirnagar University, says : “Over 80% of all mosquitoes in Dhaka are of the Culex variety and the West Nile virus could prove to be more dangerous than dengue.”

Another expert, Dr Manjur A Chowdhury, said: “The authorities should admit their failure in preventing the dengue outbreak. The number of people affected by dengue has fallen, but the future does not seem to provide any respite. The government must establish a Vector Control Research Centre to tackle the situation centrally.”

What does the West Nile virus do?

80% of people bitten by Culex mosquitoes carrying the West Nile virus, will show no symptoms, while the remaining 20% may exhibit fever, headache, or rash.Of the affected, one out of every 150 people may severely decline in health to the point of death or paralysis.

The West Nile fever has no vaccine and the only prevention method suggested is caution, that is, avoid being bitten by mosquitoes altogether.

Dr Kabirul Bashar recommended cleaning up dirty places and preventing water from stagnating around the house. He also advocated spraying insecticide every 15 days.

What are the authorities doing? 

Both city corporations in Dhaka have taken the issue seriously. The chief health officers from both the Dhaka North And South City Corporations say they have a comprehensive plan to destroy the breeding grounds of Culex mosquitoes.

Brigadier General Dr Md Sharif Ahmed, chief health officer at Dhaka South City Corporation, said: “Drains will be cleaned and waterlogging must be reduced. We will see to it. Then we will spray insecticide to destroy the larva.”

Brigadier General Dr Mominur Rahman, chief health officer at Dhaka North City Corporation, said: “From October 1, we will first start with mapping the breeding places of the Culex  mosquito. After identifying the breeding grounds, we will spray insecticide accordingly to destroy the larva at the outset. Then we will take other new and additional steps as we continue these activities.”