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Could malaria learn to infect common nuisance mosquitoes?

By Sungano Mharakurwa Moderator | 17 Jun, 2015

Hi All,
Please see abstract below and attached paper.
The malaria parasite develops virtually half-way through in culicine common "nuisance" mosquitoes. The parasite is only destroyed after it has made oocysts, the stage just before sporozites. Imagine if this adaptive parasite manages to infect the culicine mosquitoes. Nuisance mosquitoes also transmitting malaria? These tend to be more abundant and develop resistance to insecticides more readily.
Should we hasten to eliminate the malaria scourge before this happens?

Human malaria is known to be transmitted strictly by anopheline mosquitoes. Culicine mosquitoes such as Aedes spp. and Culex spp. are important vectors of other human pathogens including viruses and filarial
worms, but have never been observed to transmit mammalian malarias. Culicines do transmit avian malarias and, interestingly, allow partial development of mammalian-infectious Plasmodium parasites, implying that physiological barriers in the mosquitoes prevent parasite transmission. Although the mechanism(s) are not known, the mosquito immune system is probably involved in eliminating Plasmodium. However, Plasmodium has shown substantial capacity to adapt to new
vectors, and current ecological changes caused by humans could promote adaptation of human-infectious Plasmodium parasites to culicines. Such an event could have widespread epidemiological implications and
therefore merits attention.



Manuel Lluberas Replied at 6:37 AM, 17 Jun 2015

Adding complexity to the scenario presented, the current "vector control" interventions will also fail to have an impact on these other species. The scenario provides another reason to implement integrated vector control that attacks all developmental stages of the mosquito.

Sungano Mharakurwa Moderator Replied at 2:41 AM, 18 Jun 2015

Thanks Manuel. While it may sound like some remote possibility today, with only one stage away anything can really happen with the "thinking" malaria parasite. Now we know development of resistance to any drug is invariably a matter of when, not if. On the other hand, Plasmodium vivax is now infecting Duffy-negative communities. Meanwhile, there is now P. knowlesi on the scene. Scary thought indeed that the parasite gets so close to sporozite stage in culicines! Integrated vector control and the drive for elimination seem really imperative!

Manuel Lluberas Replied at 8:59 AM, 18 Jun 2015

This is a strong reason to start preparing for a full frontal assault on the mosquito -all mosquitoes of medical importance. Waiting until it happens will only put more lives at risk, not to mention the cost of implementing something on a "fast track" basis.

Ron Masendu Replied at 11:05 AM, 18 Jun 2015

Though not impossible, it's unlikely that nuisance culicine mosquitoes will transmit human malaria parasites in the foreseeable future. Our biggest problem now is effectively dealing with the known malaria vectors of the anopheline kind. There are major vectors in any given locality with secondary or minor vectors emerging as the vectorial system is analyzed in detail. In my view, the greatest threat lies in the other non-vector anophelines overcoming their refractory status to human malaria parasites. Our comfort is that they are largely zoophilic. Host preference is relative, especially if the species has opportunistic feeding habits. As for the culicines, if they can support parasite development then this would a disaster for humanity since they readily feed on people.

Sungano Mharakurwa Moderator Replied at 4:33 PM, 18 Jun 2015

Thanks Ron. Quite sobering possibilities indeed. One surely hopes the culicines never succumb. Does this all underscore importance of elimination then, since countries that eliminated have remained free of malaria, though the vectors are still present?

Pierre Bush, PhD Moderator Replied at 2:07 AM, 19 Jun 2015

When I read the research by Knockel, Molina et al., I was assured that avian plasmodium were not able to cause malaria in humans. Most of the chemical agents that kill anopheles can also kill culex mosquitoes. Avian Plasmodium adaptation/mutation might happen but it is not our main worry for now. But it is a good idea to have this option in mind.

Sungano Mharakurwa Moderator Replied at 3:25 PM, 19 Jun 2015

Thanks Dr. Pierre. Although Plasmodium falciparum was actually believed to be originally avian and then the theory recently challenged(http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3044689/), avian malaria parasites are indeed much less concern.

However, what seems more unsettling is evidence from the second attached Molina-Cruz et al paper (titled "An impossible journey? Development of malaria parasite NF54 in Culex quinquefasciatus". This is where it is shown that the human malaria parasite Plasmodium falciparum NF54 almost reaches sporozoite stage in the culicine. Rather unsettling, knowing the adaptive potential of P. falciparum. Hopefully we eliminate P. falciparum before this ever happens. Culex quinquefasciatus has shown resistance to a whole bunch of insecticides that may make anophelines seem a better enemy (http://www.parasitesandvectors.com/content/8/1/17; http://www.parasitesandvectors.com/content/5/1/78).

One hopes this all remains hypothetical and never becomes reality. Thanks again all for a good discussion.

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