On February 1st the WHO's IHR Committee Decision To Declare a PHEIC included a series of recommendations, including that countries follow the standard WHO recommendations regarding disinsection of aircraft and airports.
A few days later we saw the UK announce that all aircraft inbound from Zika endemic regions would be required to undergo disinsection (see UK: Aircraft Disinsection Ordered For Zika).
While preventing the inadvertent importation of Zika infected mosquitoes sounds like a good idea, with more than 500 known Zika infected travelers already in the continental United States, and probably at least 5 times that many having arrived undetected, the point is probably already moot.
Stopping the odd stowaway mosquito isn't going to do much to stop Zika transmission, since there are plenty of human carriers arriving every week.
Which is just one of the reasons why the CDC has issued guidance recommending against routine disinsection of aircraft to prevent the transportation of Zika infected mosquitoes.
Technical Statement on the Role of Disinsection in the Context of Zika Outbreaks, 2016
Limitations with Respect to the Use of Disinsection in Airplanes to Control the Spread of Zika Virus
- CDC does not recommend routine use of insecticides (disinsection) inside commercial passenger airplanes to prevent the spread of Zika virus.
- The World Health Organization (WHO) convened an Advisory Group on aircraft disinsection in Geneva during April 2016 to discuss the role of disinsection in the spread of Zika virus. In the context of Zika virus, WHO stated: “Effectiveness of disinsection was considered low for preventing pathogen importation, as there is a low risk of importation by mosquito vectors compared to infected travelers.” However, WHO continues to recognize a possible role for disinsection in certain circumstances and advises countries to conduct a risk assessment before instating requirements. It is therefore possible that individual countries may require disinsection of aircraft originating from countries with Zika outbreaks.1
- An infected person is the most common source for imported mosquito-borne viruses with a human-mosquito-human transmission cycle.2 Mosquito-borne diseases, such as dengue, chikungunya, and Zika, spread internationally primarily through infected people. This can occur when an infected person goes to a different country and is bitten by uninfected mosquitoes that then become infected. The newly infected mosquito population can then spread the disease.
- It is thought that the probability of any mosquito being on a plane is low (and perhaps even lower for an infected mosquito).3
- Given the use of air conditioning and the relatively brief period for potential exposure, the risk of travelers becoming infected on board an airplane through the bite of an infected mosquito is considered to be lower than their risk of being bitten by an infected mosquito while they were in affected areas.
- Public health interventions for travelers should focus on preventing mosquito bites while in areas with Zika virus outbreaks and on return from those areas (for 3 weeks following return).
- Routine, established efforts to control or eliminate mosquitoes in and around airports and seaports should be followed.
Although CDC has the authority to require disinsection under parts 70 and 71 of title 42 of the Code of Federal Regulations, disinsection is not currently required for airplanes or ships arriving at US ports of entry.8
- There is no evidence to show that using insecticide to kill mosquitoes inside aircraft cabins is effective in preventing introduction and spread of mosquito-borne diseases.
- Given lack of efficacy, drawbacks to consider include possible adverse health effects (including allergic reactions) in crew members or passengers , damage to aircraft materials, and objections by passengers and crewmembers.4, 5 The issue of emerging resistance to insecticides among mosquito species is another factor to weigh when considering disinsection.6
- There are currently no products approved by the Environmental Protection Agency for disinsection inside an occupied aircraft cabin.7
Humans are the Most Common Way for Zika Virus to Enter a Country
The most common way that Zika virus enters a country is by introduction of the virus to the local mosquito population by an infected traveler. Mosquito species that can transmit the Zika virus (Aedes species) are found in many parts of the United States, so infected people arriving in the United States could be bitten in their homes or residential areas by mosquitoes, which could result in local spread. For these reasons, areas where these mosquitoes are located or where Zika virus is spreading should focus on local mosquito control and other prevention efforts, such as encouraging returning travelers to take measures to prevent mosquito bites.
CDC does not recommend disinsection inside commercial passenger aircraft to be an effective approach to control the movement of Zika virus over long distances, such as from one country to another. CDC recommends that other local public health interventions should be the primary focus to prevent local transmission of Zika virus.