2.6.6. Bloodmeal identification
The proportion of bloodmeals that a vector takes on man is highly relevant to malaria transmission.
If a vector takes five bloodmeals during its lifetime and only one is on man, this vector will obviously not play any role in transmission. In contrast, if one-fifth of the mosquito population takes all its bloodmeals on man this would achieve a highly effective transmission.
Source of bloodmeals
Various methods have been devised to determine the source of bloodmeals, including direct observation, capture on human bait or characterization of the nature of the bloodmeal by serology. The latter is by far the most common procedure.
Nature of the blood
Various serological test formats have been described to identify the nature of the bloodmeal, including precipitin test, ELISA, latex agglutination and dipstick. In general, the tests are based on the identification of the nature of immunoglobulins present: this is the most readily identified blood antigen and the use of anti-immunoglobulin reagents has the advantage of being commercially available. It is easy to determine whether a mosquito has taken its blood meal on humans, on cattle or goat, but sometime more difficult to identify the animal species involved (if, for example, the source of blood is a bird or a reptile).
Picture of the whole kit used for serological identification of mosquito blood meals
The abdomen of the engorged female (or the whole mosquito) is dried on piece of filter paper and brought to the laboratory
The first stage in the identification of a blood meal is to collect abdomen of fed mosquitoes, but squashing them on a filter paper
In the laboratory, the filter paper is cut out and blood is eluted in standardized conditions. The eluate can then be used in various methods for blood meal identification
The precipitin test (i.e. double diffusion Ouchterlony test) is one of the more commonly used methods
Human blood index (HBI)
Cet index est difficile à déterminer avec précision. La procédure habituelle est de récolter autant de femelles gorgées que possible, ce qui implique la capture de moustique au repos dans les maisons, dans la zone péri-domiciliaire et, plus généralement, la "zone d'influence" du village, où l'on peut s'attendre de trouver tout moustique susceptible d'avoir pris un repas sanguin chez l'humain. Le repas sanguin est identifié plus tard en utilisant l'une des techniques standards. L'index d'anthropophilie est le pourcentage de moustiques gorgés sur humains.