A closer look at fogging

It has been a common sight for decades now all over Barbados, and indeed, other tropical countries around the world. At some point during the rainy season or when we are facing a threat of mosquito-borne diseases like dengue fever, the Ministry of Health announces a fogging schedule targeting certain districts and their environs. But have you ever wondered why mosquito control is done in this manner, how effective it is in eliminating them and whether the chemicals used are harmful to people? In this article, we hope to answer some of those questions.

The Barbados Government Information Service (BGIS) once ran a campaign stating “Where water gathers, danger lurks!” regarding the fact that mosquitoes tend to breed in pools of stagnant water. Therefore, they warn us to get rid of any open containers like old paint cans, drums used for garbage disposal, and other such receptacles around our homes, or to turn them face down if we are still using them. Large pools of stagnant water can also occur if wells or water mains are leaking in our communities and the relevant authorities or property owners are taking a long time to repair them.

So why resort to fogging? mosquitofogger.com.au, an Australia-based firm that distributes fogging machines, states,  “It is almost impossible to permanently eliminate every mosquito breeding area around the home. The most effective way to control mosquitoes is to eliminate them at their source by use of repellants or insecticides that can be applied to the area with a fogging or misting machine. These machines offer the most immediate and complete control of all options and fogging is generally the “accepted” professional process through which mosquito populations can be controlled or regulated. A fogger is a device used to disperse liquid chemicals over large areas with a very small droplet size. The small droplet size allows the chemicals to disperse and penetrate deep foliage killing mosquitoes where they hide.”

 According to a report from the World Health Organisation regarding a vector control programme in the Solomon Islands in 2014, “The aim of the mosquito fogging operations is to kill, or ‘knock-down’, any adult dengue mosquitoes that may be carrying the dengue virus. The insecticide used in mosquito fogging is a synthetic pyrethroid that is very similar to the insecticides used in most domestic insect spray cans that are found on supermarket shelves. In an article written in the Jamaica Observer in 2016, it was noted that one of the more commonly used products, Maliathon, “is an organophosphate insecticide used in agriculture, residential gardens, public recreation areas, and in public health pest control programmes. When applied in accordance with the rate of application and safety precautions specified on the label, Malathion can be used to kill mosquitoes without posing unreasonable risks to human health or the environment”. 

The type of fog used in Barbados is thermal fog. Thermal foggers use heating coils to turn a carrier solution that contains an insecticide from liquid form to a mist, smoke, or fog. Thermal foggers are ideal for outdoor use covering large yards, patios, or similar areas of mosquito infestation. Thermal foggers can operate on small butane gas cylinders making the units very portable, but must not be used in enclosed areas, due to the danger of asphyxiation. These devices typically use a hydrocarbon-based carrier solution such as diesel or kerosene oil and operate at high temperatures involving an open flame.

There are also cold foggers or Ultra Low Volume (ULV) foggers powered by electricity, which convert the fogging liquid to a fine mist which is dispersed into the air at high velocity. Cold foggers have a slightly higher efficiency than thermal foggers, as in thermal foggers a small amount of the control chemical is burnt in the fogging process. The biggest advantages to cold foggers are their ability to fog both indoors and outdoors safely as there is a reduced risk of asphyxiation, and these machines typically use water as a carrier liquid making the units very safe to handle.

The reason the procedure normally takes place late in the afternoon just prior to sunset is due to the fact that mosquitoes are more active then. We are asked to keep our windows and doors open as this will allow the fog to enter the house and kill any mosquitoes inside. The amount of insecticide in the fog is very small and is dispersed in quantities that can only kill something as small as a mosquito, so at the concentrations used there will be no adverse health effects on people who are occasionally exposed to the fog. The type of insecticide being used in the fogger is also completely odourless.

However, if you suffer from any respiratory conditions it is still important to take some precautions when the operations are taking place. If you know the times for the fogging operation in your area, and the BGIS always puts notices on the radio and in the newspapers to that effect, try not to be present to avoid any potential irritation. If you are present during fogging you can cover your mouth with a wet rag to minimise the irritation. Ensure if you are having any respiratory symptoms that you take your prescribed medication and consult your physician. And as you are often reminded as well, steer clear of the vehicle carrying out the exercise and remain indoors.

While fogging does help control the mosquito population, studies have shown that it primarily kills only adult mosquitoes but somehow protects the larvae living in the pools of water. So what is the best defense? The WHO recommends, once again, making sure there are no dengue mosquitoes breeding in your yard, such as in tyres, drums, buckets, and any water storage containers, and that you also protect your family from mosquito bites inside and outside the house during the day and in the early morning and early evening. The best methods of personal protection are to apply insect repellent and/or to wear long sleeves and long pants.

This article appears in the April 1 edition of Focus on Dengue. Read the full publication here.