Malaria Bite Prevention:
When do female Anopheles mosquitoes bite?
- biting time varies between species, so travellers should assume they are at risk of being bitten from dusk to dawn inclusive
- biting of several major malaria vectors in Africa peaks at and just after midnight so protection in bed is especially important
- however, in many parts of South America and South East Asia, the greatest risk from being bitten by malaria vectors is in the evening, before the population retires indoors
- note though - as other species of mosquito for example those which transmit yellow fever, dengue fever and other arboviral infections, bite during the daytime, it is important to maintain bite precautions during daylight hours
Measures to prevent mosquito bites
Repellents
DEET-based insect repellents are recommended as concentrations over 20% give a longer duration of protection than currently available formulations of other agents
- if DEET is not tolerated (or is not available), an alternative preparation should be used, but few are as effective as high concentrations of DEET (up to 50%) see below
DEET
- DEET (N,N-diethyl-m-toluamide) - available in a variety of concentrations and in various preparations including sprays and a slow release polymer
- low risk of adverse effects when DEET is applied according to product directions
- as a guide, duration of protection is 1 to 3 hours for 20%, up to 6 hours for 30% and up to 12 hours for 50% DEET
- sweat-off time varies with activity
- interval between applications depends on this as well as the DEET formulation and concentration used
- DEET and sunscreen
- DEET (33%) has been shown to decrease the protection from SPF 15 sunscreen (14) but there is no evidence that sunscreen reduces the efficacy of DEET when used at concentrations above 33%
- frequent (every 2 hours) reapplication of sunscreen over DEET applied at below the recommended 20% (17%), was found to reduce the mean repellency rate and also mean protection time (by about 1 hour) compared with DEET alone
- has been suggested to - apply repellent first and be aware that repellent may wear off more quickly if reapplying only sunscreen on top OR use a combined repellent and sunscreen product
- DEET is not recommended for infants below the age of 2 months
- DEET and pregnancy/breast feeding
- use of 20% DEET in the second and third trimesters of pregnancy was not associated with adverse effects on infants from those pregnancies followed for up to 12 months after birth
- given the seriousness of malaria in pregnancy, the use of DEET at a concentration of up to 50% as part of the malaria prevention regimen for pregnant women is recommended, including those in the first trimester (1)
- DEET may be used at a concentration of up to 50% in breast feeding and for infants and children aged over 2 months
- DEET for protection from mosquito bites- summary advice (1):
- DEET is suitable for all individuals over the age of 2 months (unless allergic)
- 50% has the longest duration of action, and needs fewer applications per day
- there is no current evidence that any group (including pregnant women and small children) is at increased risk from using 50% DEET
- lower concentrations are available, but:
- they need more frequent application and may not be as effective as 50%
- care must be taken to re-apply or use a higher concentration DEET preparation if mosquito biting occurs after their use
- lower concentrations are not suitable for individuals who may expect prolonged exposure, such as that encountered by backpackers and expedition travellers
- concentrations below 20% inappropriate
- DEET applications can damage some plastic watch straps, watch 'glasses' and plastic jewellery; these items should not be allowed to come into contact with DEET
- the user should ensure that repellents are not ingested or inhaled and do not come into contact with their eyes or mouth
- repellents should be used only on exposed areas of skin.
Insecticides
- permethrin and other synthetic pyrethroids have a rapid knock-down effect on mosquitoes and are used to kill resting mosquitoes in a room
Other measures:
- sleep in a screened room
- use intact mosquito nets at night
- if sleeping outdoors or in unscreened accommodation
- impregnation with permethrin 0.2g/sq m greatly enhances protection
- room protection
- air conditioning
- room could be sprayed before dusk with a knockdown insecticide (usually a pyrethroid) to kill any mosquitoes which may have entered the accommodation during the day
- use electric mat to vaporise synthetic pyrethroids overnight (electronic buzzers are useless)
- wear long sleeves and long trousers outdoors after sunset and avoid rural areas after dusk if possible
- avoid perfumes, cologne and aftershave lotion which can attract insects
Reference:
- Public Health England. Guidelines for malaria prevention in travellers from the UK 2019