American Invader Hampers the Malaria Fight in Africa

Thankfully, we're not talking about people here. It seems that a nasty weed native to America has reared its ugly head in Africa, and it's not only poisoning livestock but somehow helping starving mosquitoes survive long enough to spread malaria.

Malaria, which is delivered through the bite of a female mosquito, kills up to 755,000 people annually - most of whom are African children. That's a stunning statistic for a disease that is treatable, preventable, and not even contagious.

However, once the parasitic disease is well-established in both mosquitoes and their victims, it's very hard to eliminate. A common strategy to eliminate malaria (and most mosquito borne illnesses) is to simply keep them away from people. This not only prevents malaria exposure, but also helps cull the mosquito population.

That's because female mosquitoes rely on the essential vitamins in their blood meals to develop healthy embryos. Without blood, not only do they slowly starve (denied the few sugars they need), are also rendered barren.

And this is why the African invasion of one herb, Parthenium hysterophorus, is so alarming. According to a study recently published in the journal PLOS One, the American herb ironically called  'famine weed' can help keep starving female mosquitoes alive and healthy for longer than was once possible.

"The success of mosquitoes in transmitting diseases depends on how long they survive," Baldwyn Torto, an ICIPE scientist and lead study author explained in a statement. "Our results show that when female Anopheles mosquitoes feed on Parthenium, they survive much longer, and they also accumulate substantial energy reserves." (Scroll to read on...)

To determined this Torto and his colleagues took day-old mosquitoes and limited their access to one of three plants -- famine weed, the castor oil plant (Ricinus communis), or Bidens pilosa (a Kenyan vegetable). Two other mosquito groups were limited to either plain- or sweetened-water.

Predictably, the mosquitoes raised on sugar water fared best, with more than 60 percent surviving past 14 days without a blood meal. For the castor oil plant group, 45 percent survived.

Interestingly, despite the fact that famine weed is infamous for its toxic properties -  causing dermatitis, hay fever, and asthma in people and poisoning livestock that graze on it - 30 percent of the Parthenium group survived. The great majority of the remaining groups did not last past the first week. (Scroll to read on...)

And while 30 percent survival doesn't sound like much, it's important to note that famine weed can grow in harsh conditions where plants like R. communis cannot. In this way, the invader is simply adding to the emergency food supplies available to Africa's mosquito populations.

What's more, the mosquitoes that fed on famine weed built up larger reserves of lipids than insects fed on either of the other plants. Torto explained that lipids have high caloric value, making them particularly useful.

"For instance, lipids have been implicated in the development of embryos in mosquitoes and therefore their ability to reproduce," he said.

"Our findings point to an urgent need for focused efforts to curb the spread of P. hysterophorus, especially in malaria endemic areas," the researcher added. "The results also indicate the possible existence of disease vector species that are resilient and capable of tolerating certain cell-killing substances in the environment, including highly toxic poisons such as those produced by invasive plants. Further research is required regarding such species so as to design appropriate control strategies for them."

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