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Where do the main malaria mosquito species bite on the human body?

By Sungano Mharakurwa Moderator | 15 Sep, 2015

Hi All,
Recent research from mosquito experts suggests that covering ankles and lower extremities alone could substantially reduce biting rates. Somehow the mosquitoes hardly attempted to go higher. This may not have been suggested by the authors but one wonders whether mosquitoes can sense where the blood is most abundantly concentrated/closest to the skin surface (like bore-hole water prospecting)? Abstract is below and full paper attached.

ABSTRACT
Background: Malaria control in Africa relies heavily on indoor vector management, primarily indoor residual spraying and insecticide treated bed nets. Little is known about outdoor biting behaviour or even the dynamics of indoor biting and infection risk of sleeping household occupants. In this paper we explore the preferred biting sites on the human body and some of the ramifications regarding infection risk and exposure management.
Methods: We undertook whole-night human landing catches of Anopheles arabiensis in South Africa and Anopheles gambiae s.s. and Anopheles funestus in Uganda, for seated persons wearing short sleeve shirts, short pants, and bare legs, ankles and feet. Catches were kept separate for different body regions and capture sessions. All An. gambiae s.l. and An. funestus group individuals were identified to species level by PCR.
Results: Three of the main vectors of malaria in Africa (An. arabiensis, An. gambiae s.s. and An. funestus) all have a preference for feeding close to ground level, which is manifested as a strong propensity (77.3% – 100%) for biting on lower leg, ankles and feet of people seated either indoors or outdoors, but somewhat randomly along the lower edge of the body in contact with the surface when lying down. If the lower extremities of the legs (below mid-calf level) of seated people are protected and therefore exclude access to this body region, vector mosquitoes do not move higher up the body to feed at alternate body sites, instead resulting in a high (58.5% - 68.8%) reduction in biting intensity by these three species.
Conclusions: Protecting the lower limbs of people outdoors at night can achieve a major reduction in biting intensity by malaria vector mosquitoes. Persons sleeping at floor level bear a disproportionate risk of being bitten at night because this is the preferred height for feeding by the primary vector species. Therefore it is critical to protect children sleeping at floor level (bednets; repellent-impregnated blankets or sheets, etc.). Additionally, the opportunity exists for the development of inexpensive repellent-impregnated anklets and/or sandals to discourage
vectors feeding on the lower legs under outdoor conditions at night.

Keywords: Anopheles, Biting behaviour, Feeding behaviour, Outdoor biting, Malaria

Replies

 

Christian MAZIMPAKA Replied at 3:35 PM, 15 Sep 2015

Dear Sungano, thank you for the great work. It really shows that there are other factors to consider for the fight of Malaria. I Would like to know if there is anyone who looked out of the box and has for example examined other factors like unusual biting habit and time of the mosquitos as well as change or evolution of the mosquito species that could create resistance and can increase the disease under strict usual prevention methods.

Sungano Mharakurwa Moderator Replied at 2:58 AM, 16 Sep 2015

Thank you Christian. These are important factors that may play in unnoticed. There is evidence that some vector species may be evolving to bite early (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4416237/), compromising the effectiveness of nets and IRS.
In Zimbabwe, pyrethroid-resistant Anopheles funestus (http://www.ncbi.nlm.nih.gov/pubmed/25293669) resulted in a few districts contributing more than half of malaria burden in the whole country. Policy change on the IRS chemical of choice appears to have immediately turned the tide in Mutasa, one of those districts. We plan to run an expert panel on this experience later. There may be more success or challenge stories in the community indeed.

Pierre Bush, PhD Moderator Replied at 5:52 AM, 16 Sep 2015

This very important to know, people tend to wear long sleeved shirts and harts, now we realize that more emphasis should be put on long pants, and apply repellents to ankles! Good article.

Attached resource:

Dr. Osita Okonkwo Replied at 6:49 AM, 16 Sep 2015

Dear Sungano,

Thank you and your team for this effort.
These findings have great potentials in providing guidance on BCC components of targeted interventions that would facilitate reduction in cases of malaria among vulnerable population. Great job!

Junior Bazile Replied at 8:31 AM, 16 Sep 2015

Those are very important findings. Normally the veins are the biggest reservoir of blood in the body and when someone is sleeping in the supine position with a slight sur-elevation of the head there is more blood in the veins in the lower limbs. So the findings of this study make sense to me.

I also enjoyed going through the slides on Malaria in the US. I didn't know that Malaria was becoming such a concern in the US because of travelers coming back with the disease. That's a real case showing that the problems of the resource poor settings can be problems of the developed world.
Best,

Bazile

Sungano Mharakurwa Moderator Replied at 4:47 PM, 16 Sep 2015

Thank you Dr. Okonkwo. We need as many weapons against this disease as possible, and to use whatever works in a given area at a given time.

Sungano Mharakurwa Moderator Replied at 4:55 PM, 16 Sep 2015

Hi Junior. That is an interesting observation on malaria becoming a concern in the US. As the world is getting smaller and smaller, diseases are no longer as confined to particular countries as they used to. It is in the best interests of all to overcome these scourges and eventually eliminate them where possible.

Benjamin Ndayambaje Replied at 1:18 PM, 17 Sep 2015

I like the discussions and comments on this platform! I am among the 27 innaugural class of Masters of Science in Global Health Delivery at University of Global Health Equity Rwanda. We are in our first week orientation at Partners In Health headquarters-Rwanda.

We have a lot to share to contribute to health delivery as well as equity!

Pierre Bush, PhD Moderator Replied at 2:59 PM, 17 Sep 2015

Hello Benjamin,
Welcome in our community! You will definitely enjoy it, and learn quite a lot in here. This is one of the wells of knowledge in malariology (prevention, treatment and cutting edge research).

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