Since 1970, the occurrence of malaria has come roaring back in prevalence. Why?

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To analyze why malaria has surged since 1970, we must evaluate each statement in light of malaria transmission dynamics and historical control efforts.
Option 1: 'More vaccines exist.' This is misleading. There is no widely effective vaccine against malaria that would, by itself, cause a resurgence; in fact, vaccines have historically been limited and not sufficient to explain a widespread rebound. Thus this option misattributes the cause.
Option 2: 'Swamplands and marshes have been drained.' Draining marshes and improving drainage were common public health measures intended to reduce mosquito breeding and lower transmission, not to increase it. Therefore this would be associated with decreasing malaria risk, not explaining a rise.
Option 3: 'The use of insecticides in most countries has declined.' A reduction in insecticide use could contribute to higher transmission if it allowed mosquito populations to rebound, but this claim is too broad and lacks the direct mechanistic link shown by documented insecticide resistance. It also does not account for other influential factors like resistance dynamics and changes in malaria interventions.
Option 4: 'Malaria-carrying species of mosquitos have become resistant to insecticides.' This option aligns with well-supported evidence: widespread resistance to commonly used insecticides (e.g., pyrethroids) in Anopheles mosquitoes reduces the effectiveness of vector control programs such as indoor residual spraying and treated nets, enabling transmission to rebound and persist in many regions. This provides a concrete, plausible mechanism for the resurgence.
Option 5: 'Fewer vaccines exist.' As noted earlier, there has not been a sustained increase in malaria vaccines available; and even if vaccines were limited, the question concerns the resurgence of malaria, for which vector control and parasite resistance are more directly implicated than vaccine availability. Hence this option does not accurately explain the backslide.
Overall, the strongest and most evidence-backed explanation among the choices is that malaria-carrying species of mosquitos have developed resistance to insecticides, undermining key control measures and facilitating resurgence. The other options either describe countervailing trends (draining wetlands reducing risk), rely on inaccurate generalizations about vaccines, or fail to capture the primary mechanisms driving the increase. The incorrect choices reflect common misconceptions about vaccines, drainage projects, or blanket declines in insecticide use, rather than the established role of resistance in malaria rebound.

11:375:101:01 INTRO ENV SCIENCE Lecture #22 Quiz

Since 1970, the occurrence of malaria has come roaring back in prevalence. Why?

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