Humans, mosquitoes and bacteria: competition and survival through bednet holes, ATP-binding cassette (ABC) transporters and interferon-Y
The host-parasite relationship is formally defined as an evolutionary race (Vanaerschot et al. 2014). If the Van Valen Red Queen Hypothesis (CM Lively, available from indiana.edu/~curtweb/Research/Red_Queen%20hyp.html) is not rejected in this particular case, the enrolled species is participating in an endless game between incremental improvements in their capacity to escape host defences and the need to rid themselves of the parasitic infection. This scenario leads to the concept of a zero sum game, with the exception that from a human individual perspective, devastating consequences may arise from this game between humans and parasites (e.g., disease and epidemics). Perhaps this is the basis to describe in anthropocentric terms an almost accidental meeting that was not controlled by typical human consensus, such as the Geneva Conventions. Thus, the words strategy, ferocious, violent, attack, defence, weapons, arsenal, fight, trench, warfare, survival and struggle are among the most common words used to describe the host-parasite association in textbooks and scientific papers. Whether the result of this competition is either beneficial or harmful (from a human perspective), for every action that is designed to control a parasitic infection, a reaction from the parasite is likely (in simple terms). This reaction does not occur at an individual level, but results from the movement of millions of individuals. In the end, it is the collective action and it is the population level response that sets the scale for any evolutionary change.
In the November 2014 issue [109(7)] of Memórias do Instituto Oswaldo Cruz three papers report on the “facts and consequences of competition for survival”. In the first paper, Irish (2014) reviews the published data on the behaviour of malaria vectors in response to nets treated with insecticides. In his summary of the experimental evidence on the behaviour of Anopheles in holed bednets, the author concluded that the presence of holes did not have a significant effect on the mortality of mosquitoes in comparison with the rates in nets without holes. The key point is the time that the mosquito remains in contact with the pyrethroid-treated bednets. The data suggest that behavioural features in addition to the skill to avoid both natural and artificial barriers influenced the actual mortality rate. The author calls for more behavioural studies of Anopheles mosquitoes to improve the efficacy of this measure to control malaria transmission. In the second paper, Lima et al. (2014) reports on the involvement of ATP-binding cassette transporter (ABC transporter) proteins in the resistance of Aedes aegypti to the insecticide temephos. The authors used an ABC transporter inhibitor (verapamil) to demonstrate that in a resistant Ae. aegypti population, the toxicity of temephos increased by a factor of two. In the third paper, Lione et al. (2014) reports that interferon-γ (IFN-γ) inhibits group B Streptococcus survival within human endothelial cells. The authors show that IFN-γ contributed positively to phagosome maturation in endothelial cells, which resulted in better control of the intracellular survival of the group B Streptococcus.
Underlying these findings on mortality, resistance and survival is the evolutionary consequence of the explanation the Red Queen offered to Alice for the strange things she was experiencing in the Looking-Glass Land, which also inspired Van Valen (1973) to elaborate his Red Queen Hypothesis: "Now, here, you see it takes all the running you can do to keep in the same place”.
It is a curious fact that the biologist Leigh Van Valen (1925–2010), in the acknowledgements of his now classic paper (Van Valen 1973), makes a statement that anecdotally might be viewed as a personal account of the fitness - extinction reasoning that was detailed in that paper: “I thank the National Science Foundation for regularly rejecting my (honest) grant applications for work on real organisms (cf. Szent-Györgyi, 1972), thus forcing me into theoretical work.”.
Adeilton Alves Brandão | Publisher Editor
Irish SR 2014. The behaviour of mosquitoes in relation to humans under holed bednets: the evidence from experimental huts. Mem Inst Oswaldo Cruz 109: 905-911.
Lima EP, Goulart MOF, Rolim Neto ML 2014. Evaluation of the role of ATP-binding cassette transporters as a defence mechanism against temephos in populations of Aedes aegypti. Mem Inst Oswaldo Cruz 109: 961-963.
Lione VOF, dos Santos MHB, de Oliveira JSS, Mattos-Guaraldi AL, Nagao PE 2014. Interferon-γ inhibits group B Streptococcus survival within human endothelial cells. Mem Inst Oswaldo Cruz 109: 940-943.
Van Valen L 1973. A new evolutionary law. Evolutionary Theory 1: 1-30.
Vanaerschot M, Huijben S, Van den Broeck F, Dujardin JC 2014. Drug resistance in vectorborne parasites: multiple actors and scenarios for an evolutionary arms race. FEMS Microbiol Rev 38: 41-55.