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OP-ED: The return of La Niña and an old foe

  • Published at 12:23 am November 13th, 2020
mosquito dengue

The cold season may see a resurgence in dengue amid the pandemic

While the world is currently facing difficulties in managing the spread of the coronavirus (Covid-19), ocean and atmospheric indicators suggest the probability of an onset of La Niña, which is referred to as the cold phase of El Niño-Southern Oscillation (ENSO) cycle.

Therefore, in the wake of the devastation of the Covid-19 pandemic, many ENSO-sensitive countries could face disasters due to ongoing Covid-19, excessive winter rainfall, and the probability of an increasing number of mosquitoes and a rise in mosquito-borne diseases. When mosquitoes bite, they can transmit viruses or bacteria into our blood and make us sick. This article reviews the ongoing La Niña and provides a perspective on its impacts on the increasing number of mosquitoes and related diseases.

More mosquitoes mean more disease?

The official NOAA-Climate Prediction Center (CPC)/IRI consensus forecast (available at: https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-cpc_plume), which was published on October 8, favours La Niña (Niño-3.4 index less than -0.5°C) to persist through the Northern Hemisphere winter 2020–21 and weaken during the spring.

The latest forecasts from several models suggest the likelihood of a moderate or even strong La Niña during the peak November–January season. The forecaster consensus supports that view in light of significant atmosphere-ocean coupling already in place.

The return of the La Niña weather pattern will see more than average rainfall and a wetter winter in Bangladesh. Mosquitoes need water to complete their life cycle, and therefore, the probability of the number of mosquitoes increasing in Bangladesh during this winter season is very high. However, does that mean a consequent rise in mosquito-borne disease in Bangladesh?

From past experience, we’ve seen more mosquitoes during La Niña events, so we may well see more mosquitoes this year too. But this doesn’t necessarily mean that we’ll see more related diseases. These diseases depend on a range of factors, including elements essential to the life cycle of disease-transmitting mosquitoes.

As noted in previous studies, wet weather is important for mosquitoes because mosquitoes lay their eggs on or around stagnant or still water. This includes water in ponds, backyard plant containers, clogged gutters, floodplains, or wetlands. If the water dries up, the mosquitos die. 

Greater rainfall results in more opportunities for mosquitoes to multiply. This is how La Niña-driven rainfall causes an increased number of mosquitoes during any winter rainfall. Because Bangladesh is not free from major outbreaks of internationally significant diseases, such as dengue or malaria, there is a possibility that mosquitoes could cause dengue, malaria, or other debilitating diseases this year.

Therefore, the current challenge is figuring out how to respond to outbreaks of dengue or malaria while managing the Covid-19 pandemic. There isn’t much we can do to change the weather, but we can take steps to reduce the impacts of mosquitoes.

The most popular method is to wear insect repellent when outdoors, which helps reduce the chance of being bitten by a mosquito. But it’s also important to tip out, cover up, or throw away any water-holding container in our backyards at least once a week. Local authorities should undertake surveillance of mosquitoes and mosquito-borne pathogens, which can provide an early warning of the risk of mosquito-borne disease.

We have already seen that the spread of Covid-19 has disrupted flood response in Bangladesh. The lingering impact of La Niña and related winter rainfall will further aggravate the problem. Improper response may lead to dengue, malaria, and other similar disease outbreaks. This would ultimately spread Covid-19 and become less manageable during the peak phase of disaster, leading to further human losses and economic damage.

Therefore, local organizations and communities should play an important role in these dual disaster management challenges by utilizing scientific knowledge. As the experience of disaster management shows, various organizations including health and water should be coordinated in conducting response and mitigation. The organizations concerned with disaster management, water, humanitarian assistance, and health should provide guidelines and approaches to respond to the dual disasters of Covid-19 coupled with La Niña-related rainfall and dengue outbreaks.

Dr Md Rashed Chowdhury is PEAC-Principal Research Scientist at the Joint Institute for Marine and Atmospheric Research of the University of Hawaii, USA; Email: [email protected]

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