Chikungunya primary prevention

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]; Alonso Alvarado, M.D. [3]; Vendhan Ramanujam M.B.B.S [4]

Overview

In the absence of an effective vaccine to prevent chikungunya virus infection, the only available tool to prevent the infection is by reducing the human-vector contact.

Integrated Vector Management Program Adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

The primary vectors of chikungunya virus infection are Aedes aegypti or Aedes albopictus. Therefore, vector control planning efforts should focus on suppression of both the mosquito populations in order to prevent the likelihood of chikungunya virus infection establishment and to lay the foundation for emergency interventions in the event of an outbreak. Since the biology and control procedures for Aedes aegypti are similar to those for Aedes albopictus, surveillance and control recommendations developed for dengue management as a component of the Integrated Management Strategy for Dengue Prevention and Control (IMS-Dengue) may be utilized and intensified in order to respond to a chikungunya virus infection introduction. Successful Integrated Vector Management (IVM) for chikungunya virus infection requires trained experts in medical entomology and vector control, sufficient resources, and a sustained commitment.

Vector Surveillance and Identification of High Risk Areas

• Given the similarity in transmission cycles of both Dengue and chikungunya viruses, in areas where dengue is endemic, a retrospective analysis of Dengue virus transmission during previous years should be conducted during the chikungunya virus infection planning phase to indicate the areas where chikungunya virus infection is expected to circulate.
• Depending on the risk of transmission, stratification is done and it is used to assign resources and priorities.
• Surveillance methods for Aedes aegypti and Aedes albopictus are varied and include methods to monitor egg production, larval sites, pupal abundance, and adult abundance.
• It must also be able to detect and identify hidden and difficult to control larval sites (e.g., cryptic locations such as septic tanks, storm drains, sump pumps, and vacant lots) and other productive sites, as well as the readily identified and commonly found larval habitats.

Personal Protection

• The likelihood of the infection can be reduced by the use of personal repellents on skin or clothing. DEET (N,N-diethyl-m-toluamide) and picaridin (also known as KBR3023 or Bayrepel™) are effective repellents widely available in the America.
• Infants and others sleeping or resting during the day should use bednets to avoid infection. It is of particular importance that individuals who are potentially infected with chikungunya virus during an outbreak rest beneath an insecticide-treated (IT) bednet to avoid mosquito bites and further spread of infection.
• Use of IT bednets has an additional benefit of killing mosquitoes that come into contact with the net, which may reduce vector-human contact for other household members.
• A number of pesticide products may be used to safely treat bednets, or long-lasting pretreated nets can be obtained commercially.

WHO recommended insecticide products for treatment of mosquito nets

Insecticide	Formulation	Dosage (milligrams of active ingredient per square meter of netting)
Alpha-cypermethrin	SC 10%	20−40
Cyfluthrin	EW 5%	50
Deltamethrin	SC 1%; WT 25%; and WT 25% + Binderd (K-O TAB 1-2-3®)	15−25
Etofenprox	EW 10%	200
Lambda-cyhalothrin	CS 2.5%	10−15
Permethrin	EC 10%	200−500
EC = emulsifiable concentrate; EW = emulsion, oil in water; CS = capsule suspension; SC = suspension concentrate; WT = water dispersible tablet
Table adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

WHO recommended long-lasting pretreated nets

Product name	Product type
ICON® MAXX	Lambda-cyhalothrin 10% CS + Binder (Target dose of 50 mg/m2)
CS = capsule suspension
Table adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

Household Prevention

• The use of intact screens on windows and doors will reduce entry of vectors into the home.
• Mosquito proofing water storage vessels will reduce oviposition sites and local production.
• Within a household, use of IT bednets and IT curtains also reduce vector-human contact.
• The number of adult mosquitoes in a home may be reduced by using commercially available pyrethroid-based aerosol sprays and other products designed for the home, such as mosquito coils and electronic mat vaporizers.
• Aerosol sprays may be applied throughout the home, but areas where adult mosquitoes rest (dark, cooler areas) must be targeted, including bedrooms, closets, clothing hampers, etc.
• Care should be taken to emphasize proper use of these products when advocating their application to the public, in order to reduce unnecessary exposure to pesticides.

Neighborhood and Community Prevention

• Neighborhood and community prevention for a chikungunya virus introduction in the Americas should be based on methods developed for dengue control that will reduce the probability that a viremic human arriving in the Americas will be fed upon by Aedes aegypti or Aedes albopictus mosquitoes, thereby leading to secondary transmission and potential establishment of the virus.
• Dengue programs for controlling Aedes aegypti have traditionally focused on control of immature mosquitoes, often through the community’s involvement in environmental management and source reduction thereby stressing on the importance of incorporating community involvement into an IVM program.

Vector Control Procedures

There are a number of vector control procedures that should be consulted when establishing or improving existing programs, which are considered to mitigate the risk of virus expansion.

Environmental Management

• Reduce larval habitats
• Manage (wash/cover) containers
• Discard/recycle containers
• Reduce human-vector contact
• Install window screens

Larval Control

• Source reduction
• Biological control
• Chemical control

WHO-recommended compounds and formulations for control of mosquito larvae in container habitats

Insecticide	Formulation†	Dosage (mg/L of active ingredient for control of container-breeding mosquitoes)	WHO hazard classification of active ingredient‡
Organophosphates
Pirimiphos-methyl	EC	1	III
Temephos	EC, GR	1	U
Insect growth regulators
Diflubenzuron	DT, GR, WP	1	U
rs-methoprenee	EC	1	U
Novaluron	EC	0.01-0.05	NA
Pyriproxyfene	GR	0.01	U
Biopesticides
Bacillus thuringiensise israelenses	WG	1-5 mg/L	U
Spinosad	DT, GR, SC	0.1-0.5	U
†DT = tablet for direct application; GR = granule; EC = emulsifiable concentrate; WG = water-dispersible granule; WP = wettable power; SC = suspension concentrate ‡ Class II = moderately hazardous; Class III = slightly hazardous; Class U = Unlikely to pose an acute hazard in normal use; NA = not available
Table adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

Adult Mosquito Control

• Use of IT bednets
• Use of IT curtains
• Lethal ovitraps
• Space sprays
• Indoor residual treatments

Examples of insecticides for cold aerosol or thermal fog application against mosquitoes

Insecticide	Chemical	Cold aerosols (Dosage of active ingredient (g/ha)	Thermal fogs (Dosage of active ingredient (g/ha)	WHO hazard classification of active ingredient†
Fenitrothion	Organophosphate	250−300	250−300	II
Malathion	Organophosphate	112−600	500−600	III
Pirimiphos-methyl	Organophosphate	230−330	180−200	III
Bioresmethrin	Pyrethroid	5	10	U
Cyfluthrin	Pyrethroid	1−2	1−2	II
Cypermethrin	Pyrethroid	1−3	−	II
Cyphenothrin	Pyrethroid	2−5	5−10	II
d,d-trans-Cyphenothrin	Pyrethroid	1−2	2.5−5	NA
Deltamethrin	Pyrethroid	0.5−1.0	0.5−1.0	II
D-Phenothrin	Pyrethroid	5−20	-	U
Etofenprox	Pyrethroid	10−20	10−20	U
λ Cyhalothrin	Pyrethroid	1.0	1	II
Permethrin	Pyrethroid	5	10	II
Resmethrin	Pyrethroid	2-4	4	III
†Class II = moderately hazardous; class III = slightly hazardous; class U = unlikely to pose an acute hazard in normal use; NA = not available
Table adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

WHO recommended insecticides for use as indoor residual sprays

Insecticide compounds and formulations	Class group†	Dosage (g a.i./m2)	Mode of action	Duration of effective action (months)
DDT WP	OC	1−2	contact	>6
Malathion WP	OP	2	contact	2-3
Fenitrothion WP	OP	2	contact & airborne	3-6
Pirimiphos-methyl WP & EC	OP	1−2	contact & airborne	2-3
Bendiocarb WP	C	0.1−0.4	contact & airborne	2-6
Propoxur WP	C	1−2	contact & airborne	3-6
Alpha-cupermethrin WP & SC	PY	0.02−0.03	contact	4-6
Bifenthrin WP	PY	0.025−0.05	contact	3-6
Cyfluthrin WP	PY	0.02−0.05	contact	3-6
Deltamethrin WP, WG	PY	0.02−0.025	contact	3-6
Etofenprox WP	PY	0.1−0.3	contact	3-6
Lambda-cyhalothrin WP, CS	PY	0.02−0.03	contact	3-6
†CS = capsule suspension; EC = emulsifiable concentrate; SC = suspension concentrate; WG = water dispersible granule; WP = wettable; OC = Organochlorines; OP = Organophosphates; C = Carbamates; PY = Pyrethroids
Table adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

Resistance Testing

Frequent application of the same insecticide or class of insecticide may select for individual mosquitoes that are able to survive pesticide applications. Resistance is a heritable change in the sensitivity of a mosquito population to an insecticide that may lead to failure of the pesticide to yield the expected degree of control. The insecticides available for use as adulticides are limited, and fall into three chemical classes: organophosphates, carbamates, and pyrethroids. Some products for larviciding have different modes of actions, such as insect growth regulators and microbials tools. However, the most commonly used product for controlling larvae of Aedes aegypti in containers is the organophosphate temephos. Resistance to temephos has been detected in multiple Aedes aegypti populations in the Americas and poses a serious threat to Aedes aegypti control. Little information is available about resistance in Aedes albopictus populations in the region.

Supervision, Safety, and Quality Assurance

Continuous monitoring and supervision are required to ensure that staff are adequately trained and are following appropriately technical guidelines for pesticide application and personal safety.

• IVM programs must include a quality assurance program designed to monitor the effectiveness of the control activities.
• A quality assurance program should monitor applicator performance and control outcomes.
• Control failures may be due to misapplication, incomplete coverage, or insecticide resistance, and must be corrected immediately.
• Quality assurance efforts should be continuous, systematic, and independent.

Vector Control for chikungunya virus Containment

The purpose of containment is to eliminate the newly introduced chikungunya virus and to prevent its spread by implementation of intensive vector control measures. The following actions are recommended to contain an introduction of chikungunya virus.

• In addition to participating in a national communication effort, the community (residents, schools, churches, businesses, etc.) has to be informed of the chikungunya virus introduction immediately.
• Conduct indoor and outdoor insecticide applications to eliminate adult mosquitoes.
• Simultaneously conduct container elimination or protection and larviciding to eliminate the production of new mosquitoes.
• Alternatively, or concurrently with source reduction, residual insecticides can be applied to containers holding non-potable water (to inner or outer walls) to kill the larvae and pupae and to nearby outdoor surfaces to kill landing or resting adult mosquitoes.
• Monitor houses and buildings in the neighborhoods that are being treated and implement special control rounds after working hours, weekends, and holidays to assure that nearly 100% of homes and businesses are treated.
• Controlling an epidemic of chikungunya virus or a series of outbreaks over a larger geographic scale requires the following
  • Activating a command center (Emergency Operations Center), either physical or virtual, where epidemiologists, entomologists and vector control specialists, educators, media communicators, etc., can jointly plan, work, and evaluate progress throughout the epidemic.
  • Orienting the population at large through the media on the possibility of resulting infection with chikungunya virus and on how families and communities can contribute to the abatement of the epidemic.
  • Ensuring that infected and febrile persons are protected from mosquito bites by using bednets at home and in hospitals.
  • Orienting vector control operations through real-time epidemiological and entomological assessments of chikungunya virus transmission, indicating the specific areas that need to be treated.
  • Applying effective vector control measures, which are similar to those recommended for area-wide chikungunya virus containment and dengue virus outbreaks.

Response to chikungunya virus Infection Introduction Adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

• Immediately upon confirmation of the first autochthonous chikungunya virus case, the health department should inform the IVM program regarding the onset date and location of the case. Vector control procedures must be intensified to effectively reduce the abundance of infected vectors in order to halt transmission in the areas of the case(s).
• Simultaneously, emergency response committees at local and national levels should be informed of the situation and activated. Initial efforts should focus on containing virus transmission and preventing expansion. If virus containment fails, or if cases are not detected until the outbreak has spread over a large geographic area, intensive vector control efforts will need to be expanded to a larger scale program.

Risk and Outbreak Communication Adapted from Preparedness and Response for chikungunya virus: Introduction in the Americas. PAHO © 2011.

• Communications are an integrated, coordinated effort involving all disciplines and components for preparation and response.
• Timely communication with stakeholders is crucial for enlisting the community’s participation and to avoid confusion and misinformation.
• As chikungunya virus is novel in the Americas, the media, the public and many officials will need to be educated about the disease, the mode of transmission, the lack of specific therapeutic treatment, means of symptomatic and supportive treatment, and effective control measures.

External Links

• CDC chikungunya virus