Methods in Anopheles Research - MR4

Chapter 2 : Anopheles Laboratory Biology and Culture2.2 Infections in Mosquito CulturesPage 1 of 102.2 Infections in Mosquito CulturesJames J. Becnel and Paul HowellIntroductionFortunately, there are few naturally occurring pathogens that become established in mosquito colonies.There are, however, numerous microbes living within an insectary which, under normal conditions, arenot considered pathogenic (capable of causing disease) but may have deleterious effects when aninsect colony is stressed. Environmental stressors include larval overcrowding, unstable heat or humidity,poor quality diet and overfeeding.Infections in the insectary are spread through one of the following routes: diet, injury, infestation of theegg, or environment. Dietary routes include feeding insects a contaminated diet or the cannibalism ofexpired, infected larvae. Larval injury creates an opening for many water-borne pathogens. Insect eggscan be either internally (viruses) or externally (fungi or microsporidia) infected.Environmental routes are non-specific but can include the following:Introduction of pathogens by wild strains- Wild or newly acquired insects can carry pathogens which donot affect them in the wild, but when introduced in a newly stressed atmosphere, these pathogens canbecome opportunistic. Also, a newly acquired laboratory colony can introduce a chronic infection to aninsectary.Airborne entry- Several fungi, bacteria, and protists can be introduced on airborne particles.People- Some of the more common bacterial contaminants in insect colonies are considered normalhuman fauna like Escherichia coli. These can be passed to the water by touching the water or food whilefeeding.Surfaces- Contaminated or poorly cleaned surfaces and equipment can harbor large numbers ofopportunistic microbes.Knowing what a healthy colony looks and smells like can be the easiest way to detect an infection. Waterthat is malodorous, cloudy, has persistent bubbles or contains excessive foreign matter may bedetrimental to an insect colony (see Chapter 2.4.5 for more on water quality). In the insects, signs andsymptoms can include changes in normal size or color, deformity, lengthened duration of rearing, reducedlongevity of adults, decreased fecundity, and decreased fertility rates. Excess mortality, short life-spans,low reproductive rates, or the presence of fungi on the cuticle are some of the early signs of a possibleinfection in a colony.Infected larvae typically display one of the following: deformation (Figure 2.2.1 and 2.2.2), ordiscoloration of the larvae as well as abnormal larval behavior. In pupae, typical signs of infectionsinclude elongation of early pupae, failure to emerge (Figure 2.2.3), or selective emergence of one sex.