Anopheles gambiae

The ''Anopheles gambiae'' complex consists of at least seven morphologically indistinguishable species of mosquitoes in the genus ''Anopheles''. The complex was recognised in the 1960s and includes the most important vectors of malaria in sub-Saharan Africa, particularly of the most dangerous malaria parasite, ''Plasmodium falciparum''. It is one of the most efficient malaria vectors known. The ''An. gambiae'' mosquito additionally transmits ''Wuchereria bancrofti'' which causes lymphatic filariasis, a symptom of which is elephantiasis.

Discovery and elements

The ''Anopheles gambiae'' complex or ''Anopheles gambiae'' sensu lato was recognized as a species complex only in the 1960s. The ''A. gambiae'' complex consists of:
* '' Anopheles arabiensis''
* ''Anopheles bwambae''
* ''Anopheles melas''
* ''Anopheles merus''
* ''Anopheles quadriannulatus''
* ''Anopheles gambiae'' sensu stricto (s.s.)
* '
* ''Anopheles amharicus''

The individual species of the complex are morphologically difficult to distinguish from each other, although it is possible for larvae and adult females. The species exhibit different behavioural traits. For example, ''Anopheles quadriannulatus'' is both a saltwater and mineralwater species. ''A. melas'' and ''A. merus'' are saltwater species, while the remainder are freshwater species.
''Anopheles quadriannulatus'' generally takes its blood meal from animals (zoophilic), whereas ''Anopheles gambiae'' sensu stricto generally feeds on humans, i.e. is considered anthropophilic.
Identification to the individual species level using the molecular methods of Scott ''et al.'' (1993) can have important implications in subsequent control measures.

''Anopheles gambiae'' in the strict sense

''An. gambiae sensu stricto'' (s.s.) has been discovered to be currently in a state of diverging into two different species—the Mopti (M) and Savannah (S) strains—though as of 2007, the two strains are still considered to be a single species.

The mechanism of species recognition appears to be sounds emitted by the wings and identified by Johnston's organ.

Genome

''An. gambiae'' s.s. genomes have been sequenced three times, once for the M strain, once for the S strain, and once for a hybrid strain. Currently, ~90 miRNA have been predicted in the literature (38 miRNA officially listed in miRBase) for ''An. gambiae'' s.s. based upon conserved sequences to miRNA found in ''Drosophila''. Holt ''et al.'', 2002 and Neafsey ''et al.'', 2016 find transposable elements to be ~13% of the genome, similar to ''Drosophila melanogaster'' (also in Diptera). However they find the proportion of TE types to be very different from ''D. melanogaster'' with approximately the same composition of long terminal repeat retrotransposons, non-long terminal repeat retrotransposons and DNA transposons. These proportions are believed to be representative of the genus.

The genetics and genomics of sex chromosomes have been discovered and studied by Windbichler ''et al.'', 2007 and Galizi ''et al.'', 2014 (a ''Physarum polycephalum'' homing endonuclease which destroys X chromosomes), Windbichler ''et al.'', 2008 and Hammond ''et al.'', 2016 (methods to reduce the female population), Windbichler ''et al.'', 2011 (trans from yeast), Bernardini ''et al.'', 2014 (a method to increase the male population), Kyrou ''et al.'', 2018 (a female necessary exon and a homing endonuclease to drive it), Taxiarchi ''et al.'', 2019 (sex chromosome dynamics in general) and Simoni ''et al.'', 2020 (an X chromosome destroying site specific nuclease). See below for their applications.

''An. gambiae'' has a high degree of polymorphism. This is especially true in the cytochrome P450s, Wilding ''et al.'', 2009 finding 1 single nucleotide polymorphism (SNP)/26 base pairs. This species has the highest amount of polymorphism in the CYPs of any insect known, much tending to be found in "scaffolds" that are found only in particular subpopulations. These are termed "dual haplotype regions" by Holt ''et al.'', 2002 who sequenced the strain.

In common with many chromosomes, ''An. gambiae'' codes for spindle and kinetochore-associated proteins. Hanisch ''et al.'', 2006 locate '' AgSka1'', the spindle and kinetochore-associated protein 1 gene, at EAL39257.

The entire Culicidae family may or may not conserve epigenetic mechanisms this remains unresolved. Toward answering this question, Marhold ''et al.'', 2004 compare their own previous work in ''Drosophila melanogaster'' against new sequences of '' D. pseudoobscura'' and ''An. gambiae''. They find all three do share the DNA methylation enzyme DNMT2 ('' DmDNMT2'', '' DpDNMT2'', and '). This suggests all Diptera may conserve an epigenetic system employing Dnmt2.

Hosts

Hosts include '' Bos taurus'', ''Capra hircus'', ''Ovis aries'' and '' Sus scrofa''.

Parasites

Parasites include ''Plasmodium berghei'' (for which it also serves as a vector), and the bioinsecticides/entomopathogenic fungi ''Metarhizium robertsii'' and '' Beauveria bassiana''. All three of these parasites combine with insecticides to reduce fitness see below. CRISPR/Cas9 and U6-gRNA are increasingly () being used together for knockout experiments in mosquitoes. Dong ''et al.'', 2018 develops and presents a new U6-gRNA+Cas9 technique in ''An. gambiae'', and utilizes it to knock out fibrinogen related protein 1 (FREP1), thereby severely reducing infection of the mosquito by ''P. berghei'' and '' P. falciparum''. However this also demonstrates the centrality of FREP1 to the insect's success, impairing all measured activities across all life stages. Yang ''et al.'', 2020 uses the Dong method to do the same with '' mosGILT'', also severely reducing ''Plasmodium'' infection of the mosquito but ''also'' finding a vital life process is impaired, in ''mosGILT''s case ovary development.

Control

Insecticides

Parasites/bioinsecticides and chemical insecticides synergistically reduce fitness. Saddler ''et al.'', 2015 finds even ''An. gambiae'' with knockdown resistance (''kdr'') are more susceptible to DDT if they are first infected with ''Plasmodium berghei'' and Farenhorst ''et al.'', 2009 the same for ''Metarhizium robertsii'' or '' Beauveria bassiana''. This is probably due to an effect found by Félix ''et al.'', 2010 and Stevenson ''et al.'', 2011: ''An. gambiae'' alters various activities especially CYP6M2 in response to ''P. berghei'' invasion. CYP6M2 is known to somehow produce pyrethroid resistance, and pyrethroids and DDT share a mechanism of action.

Gene drive

Research relevant to the development of gene drive controls of ''An. gambiae'' have been performed by Windbichler ''et al.'', 2007, Windbichler ''et al.'', 2008, Windbichler ''et al.'', 2011, Bernardini ''et al.'', 2014, Galizi ''et al.'', 2014, Hammond ''et al.'', 2016, Kyrou ''et al.'', 2018, Taxiarchi ''et al.'', 2019 and Simoni ''et al.'', 2020. For specific genes involved see above. These can all be used in pest control because they induce infertility.

Fecundity

Fecundity of ''An. gambiae'' depends on the detoxification of reactive oxygen species (ROS) by catalase. Reduction in catalase activity significantly reduces reproductive output of female mosquitoes, indicating that catalase plays a central role in protecting oocytes and early embryos from ROS damage.

Historical note

''An. gambiae'' invaded northeastern Brazil in 1930, which led to a malaria epidemic in 1938/1939. The Brazilian government assisted by the Rockefeller Foundation in a programme spearheaded by Fred Soper eradicated these mosquitoes from this area. This effort was modeled on the earlier success in eradication of ''Aedes aegypti'' as part of the yellow fever control program. The exact species involved in this epidemic has been identified as '' An. arabiensis''.

Peptide hormones

Kaufmann and Brown 2008 find the ''An. gambiae'' adipokinetic hormone (AKH) mobilizes carbohydrates but not lipids. Meanwhile AKH/Corazonin Peptide (ACP) does not mobilize (or inhibit mobilization) of either. Mugumbate ''et al.'', 2013 provides in solution and membrane bound structures from a nuclear magnetic resonance investigation.

References

External links

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DiArk
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gambiae
Insect vectors of human pathogens
Animal models
Insects described in 1902