ANSWERS TO DR. SAPNA'S QUESTIONS

THE QUESTIONS ARE:

1.Why is a second fogging done around a case of Dengue?
2.Why on the 7th day after the first fogging?
3.What is the insecticide used for fogging?What is the mechanism of action and the quantity in which it is used?
4.What are the different type of sprays used for fogging?

THE ANSWERS
(taken from Park's Textbook of Preventive and Social Medicine 17th edP544-548)

Question 1: It is done to kill any missed infected adult mosquitoes and newly grown adult mosquitoes from an infected pupa.

2. If an infected female mosquitoe so happen to lay eggs on the first fogging, the 'infected eggs' are protected from the fogging effect as the fog only effective in killing adult mosquitoes. The eggs will reach larva stage at day 5-7 and pupa stage at 6-7 days. A second fogging is done on day 7 to kill the Culicine (Culex, Aedes, and Mansonia) larvae through their siphon tube that is attached to its 8th segment of its body that is exposed to the air. But the main idea of fogging on 7th day is to kill the pupa. The pupa represents the resting stage in the life history of the mosquito.It has 2 small respiratory tubes (trumpets) project from the upper surface of the thorax, therefore the fod or mist sprayed on 7th day will effectively kill them as well.

3. The insecticide used in Malaysia for fogging normally is Resigen (S-bioallethrin, permethrin (25/75) and piperonyl butoxide). S-bioallethrin and Permethrin belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. Piperonyl butoxide (PBO) is a pesticide synergist and also a potent cytochrome P450 inhibitor. It does not, by itself have pesticidal properties.
The quantity used in oil-based will be 1L of Permethrin (100mL of Resigen :1L of Diesel). *note, the fogging machine can fit 5.5L but the staffs prepare 5L of mixtures.

4. Other types of spray used are:
Residual insecticide (Malathion and fenitrothion) using ULV fogging.