Methods in Anopheles Research - MR4

Chapter 2 : Anopheles Laboratory Biology and Culture2.2 Infections in Mosquito CulturesPage 2 of 10Figure 2.2.1. Anophelesstephensi larvae that failedto complete metamorphosisdue to infection.Figure 2.2.2. Anopheles gambiaeshowing deformation and signs ofinfection in the larval state.Figure 2.2.3. InfectedAnopheles stephensi thatdied during ecdysis.Commonly reported infections in mosquito coloniesThere are two forms of infections in a colony: chronic and acute. Chronic infections may persist forseveral generations and never be fully apparent but result in poor quality insects, such as infections withfungi and protozoa. Conversely, acute infections quickly spread through a colony and lead to highmortality rates. Pathogens that have been implicated as agents of acute infections include bacteria,viruses, and some fungi. Although the following is not a complete list, it covers the most reportedpathogens and if possible, includes a description of the microbe or the appearance of the infected insect.VirusesThe two types of viruses routinely found to be pathogenic to mosquitoes are defined as occluded or nonoccluded(Federici 1985). Although not routinely found in insectary populations, there have been viralinfections reported in laboratory colonies of An. stephensi. One of these reports showed high mortalityrates in the colony associated with this infection (Bird et al. 1970). At least two other types of viruses havebeen isolated from mosquitoes with only one being reported as detrimental to development of the larvae(Jenkins 1964).Occluded Viruses (Becnel and White 2007)These viruses form proteinaceous crystal occlusions within the mosquito.BaculoviridaeDeltabaculovirus: This Dipteran-specific NPV is the only member of this family that is commonlyassociated with feral mosquito larvae. These viral particles infect the larval midgut epithelium resulting ina stunted appearance, delayed growth and death. Infected larvae often have white cysts or nodulesthroughout the midgut and gastric cecae. These virions are highly virulent and cause mortality within 72-96 hours after the initial infection. Transmission of the virus is enhanced with a high concentration of Mg 2+cations in the larval habitat (Becnel 2007).ReoviridaeCypovirus: These are also referred to as cytoplasmic polyhedrosis viruses (CPV). Infections with CPVsare typically benign in nature but can cause larval mortality when present in high numbers. Infections areeasily seen in L3 or L4 larvae as opaque sections limited to the gastric caeca and/or posterior stomach.Transmission of these viruses is enhanced in the presence of divalent cations or when larvae arestressed.