Frequently Asked Questions
1. What is larviciding?
In the context of malaria control, larviciding is one of the vector control interventions aimed at killing the immature aquatic stages of the mosquito vector. For best results in a control programme, it should be deployed as part of an integrated vector management (IVM) strategy.
2. Why should we larvicide?
Larviciding, unlike other vector control measures such as indoor residual spraying (IRS) and use of long lasting insecticide treated bed nets (LLINs), it targets the larva at source thereby reducing the number of adult mosquitoes which will emerge from a productive (infested) water body to bite people in the neighbourhood. In this respect, it is effective on both outdoor and indoor biting vectors unlike IRS and LLINs .
3.How does a larvicide work?
There are various ways in which a larvicide works to kill the mosquito larvae depending on the type of larvicide used
Suffocating the larvae and pupae
Acts on the nervous system of larvae
Bacteria (eg Bacillus thuringiensis israelensis) is ingested and attacks the gut lining causing the vector to stop feeding and its eventual death.
Prevention of emergence into adults. This is possible with use of insect growth regulators (IGRs)
4. Where & when should we apply a larvicide?
Larvicides should only be applied in a water body detected to have mosquito larvae. There is no benefit in treating unproductive pools. The residual effect of a larvicide will wane within a fortnight or diluted with rain water allowing breeding to re-establish. Breeding often occurs at the edges of a pool or pond where eggs are sheltered from inclement weather conditions such as wind. As a rule of thumb, larviciding is conducted fortnightly on a previously infested site. However, there are some long acting larvicides which lasts up to a month or more.
5. Is larviciding safe?
A larvicide, just like other insecticides, must be tested for efficacy and safety before use in a vector control programme. Reagent Laboratory has a number of products which have been approved by health authorities in various countries. (Bti) and temephos are 2 active ingredients that have passed the World Health Organisation Pesticide Evaluation System (WHOPES). Despite their safety profile, spray operators are required to wear appropriate personal protective clothing.
6. Is larviciding the same as larval source management (LSM)?
The answer is NO. Most people confuse these 2 terms and use them interchangeably. Larviciding is part of LSM. LSM encompasses environmental measures (modification and manipulation) and biological means using predators such as larvivorous fish. Larviciding occupies significant part in the larval source management for malaria control. Larval source management as a vector control tool only received much attention from WHO in 2012 and is arguably the forgotten tool in vector control
B. SPACE SPRAYING (FOGGING)
1. What is fogging?
Space spraying or fogging as it is commonly called, is the spraying of insecticide into the air (open space) to form tiny droplets (less than 50µm in diameter) which remain airborne to kill flying insects. The aerosols can either be in the form of cold or hot fog. The latter is often seen as thick clouds of smoke while cold fogs are less visible.
2. Why conduct space spraying?
The goal of space spray is to reduce the risk of human disease by killing potential vectors and infected adult female mosquitoes. The following are sufficient grounds for implementing space spray;
When there is evidence from surveillance data suggesting a high risk of human infection.
When there is abundant(high densities) adult mosquitoes
In disease outbreak situations especially with high human population densities.
3. Where & when should fogging be done?
A good knowledge of the vector behaviour is important before planning a space spraying programme. In the case of the malaria mosquito.
4. What equipment is used when fogging?
Basically there are 2 broad categories of equipment used when fogging (ground space spraying). Vehicle mounted fogging machines are suitable where there are well defined roads but the less accessible areas in between buildingsrequireportable or hand held machines. For very large applications aircrafts are used but this is very rare or non-existent in malaria control programmes on the African continent.
5. How often should I fog?
Unlike other vector control interventions which are applied less frequently, fogging is more demanding. Fogging aims to kill a moving target in two phases of a fogging programme. It has no residual effect. The initial stage is the attack phase (every other day) which aims to interrupt breeding cycle followed by the maintenance phase conducted once or twice per week. The mosquito population recovers within a week or two after fogging since larvae are not affected during fogging. Depending on the size of droplets (aerosols) and weather conditions, the treatment will not last beyond 14 minutes for droplets 20 microns in size
6. Is fogging safe?
Provided the operator, assistants and supervisor as the case may be use the recommended protective clothing, there is little risk of inhaling fumes. However, fogging is less specific in its action and will kill non target pests.
Malariais a life threatening diseasecaused by Plasmodiumparasite that commonly infects the female Anopheles mosquitoes which feed on humans. People who get malariaare typically very sick with high fevers, shaking chills, and flu-like illness.
According to the Global Malaria Programme (GMP) WHO Malaria terminology, a malaria vector “is the adult females of any mosquito species in which Plasmodiumundergoes its sexual cycle (whereby the mosquito is the definitive host of the parasite) to the infective sporozoites stage (completion of extrinsic development), ready for transmission when a vertebrate host is bitten”.
Mosquitoes are not born with malaria but get infected by when they bite a malarious case. It is only after a blood meal infected with gametocytes (sexual stage of parasite) that they become a public health problem. The gametocytes develop and multiply within the mosquito but unlike in humans,donotmake the mosquito noticeably sick! The mosquito then inoculates the parasites ((sporozoites) into the secondary host (human).
Of the 3,500 mosquito species, it is the Anopheleswhich is capable of transmitting malaria. And not all anophelines are vectors for transmitting malaria from one person to another. In Southern Africa, the primary vectors areAnopheles gambiaeand Anopheles funestus.
The World Health Organisation defines IVM as “a rational decision-making process for the optimal use of resources for vector control”. IVM does not rely on one malaria control intervention but deploys these measures in a coordinated sustainable manner. Vector control measures available include-IRS, LSM, LLINs, environmental manipulation and modification.
D. IRS (INDOOR RESIDUAL SPRAYING)
1. What is IRS?
Indoor residual spraying (IRS) as it is commonly known is one of the vector control interventions which involves the application of an approved long-acting, residual insecticide to interior walls of human dwellings, eaves and ceilings for the purpose of killing malaria mosquitoes when they come into contact with the treated surfaces.
2. Why IRS?
Interior surfaces coated with a long acting WHO approved insecticide kills mosquitoes (and other insects) landing on it either before but mainly after the blood meal. This reduces the malaria transmission as the already infected mosquito (carrying sporozoites) will die before inoculating humans. Furthermore, IRS reduces the mosquito density when >80% spray coverage is achieved.
For IRS to work effectively, the female mosquito vector must be indoor resting (endophilic) and in most cases also endophagic (indoor feeding). The mosquito rests on the sprayed wall either before or after having a blood meal but very often the latter when it is engorged with blood. When the vector is contaminated with insecticide it dies before transmitting sporozoites to the next person and thus reduce density and longevity of mosquitoes. In order to have malaria reduction, the IRS coverage must be above 85%
As pointed out earlier, only on human structures and also animal shelters in close proximity to residential premises. This must be done by well-trained Spray Operators.
Timing of IRS is essential in order to get desired results. In areas where malaria is seasonal, like some countries in Southern Africa (Zimbabwe, Zambia, Botswana) IRS is conducted before the onset or at the beginning of the rainy season. Ideally, IRS should not last more than 2 months and must not progress into the peak malaria transmission period.
6. What is a spray round and spray cycle?
When a team of spray operators embarks on a spraying programme in an area over a period of time, this is referred to as a spray round. The activity lasts 2-3 months depending on terrain and resources available to the programme. To be effective, spray round implementation should be:
Total: all the dwellings are sprayed or at least 80%;
Complete: all sprayable surfaces are covered without leaving areas which will be used as landing platforms as mosquitoes avoid insecticide;
Sufficient:uniform application of the required dose to all sprayable surfaces; and
Regular: spraying should be at regular intervals so as to ensure that an effective residue is in place during the whole malaria transmission season
On the other hand, the repetition of spray rounds at regular intervals is the “spraying cycle”. It is the time between consecutive spray rounds. More information on spray cycle is provided below.
7. Frequency of IRS application (Spraying cycle) is dependent on 3 factors
The longevity of residual insecticide used. For example, DDT and other pyrethroids like lambdacyhalothrin and deltamethrin if applied correctly and at the right dosage (i.e. grams active ingredient/m²) will last >6 months for DDT and 3-6 months for the pyrethroids.
The insecticide formulation. A wettable powder, capsule suspension and suspension concentrate will generally last longer on sprayable surfaces than emulsion concentrate
Endemicity of area being sprayed. In areas with perennial transmission of malaria, it is advisable to conduct 2 spray rounds unless the product being used has a residual period sufficient to last at least 10 months as is the case with some CS formulations and DDT
The World Health Organisation recommends a list of insecticides as outlined in section 2.3.4 www.who.int/whopes/en. Regent laboratories supplies one of the compounds-lambda cyhalothrin (Bugstop WP)
9. What is spray coverage?
In the attack phase of the control programme, a minimum of 80% coverage should be attained and scaled up to 85% coverage to achieve “mass effect”.A high coverage has an impact on vector populations and malaria transmission. Coverage is calculated by taking into account the totalnumber of sprayed rooms or houses/total number of targeted rooms or houses. The more accurate indicator for coverage is by using rooms since houses will do not always have the same or equal number of rooms.
10. Is IRS safe?
All insecticides should be handled with caution as they are capable of poisoning the operator and environment if not used according to manufacturer’s instructions. If the National Malaria Control Programme (NMCP) uses carbamates and organophosphates, it is important to take note of the stringent recommendations by the WHO Expert Committee on Vector Biology & Control which advocates for routine cholinesterase monitoring, wearing of protective clothing, and high standard of personal hygiene.
Failing to follow correct procedures during spraying operations can result in undesired exposure to insecticides or accidental insecticide poisoning.