Repeat infection with malaria parasites might make mosquitoes more dangerous

July 16, 2015
If they have the opportunity mosquitoes will blood feed every 2-5 days and therefore can be exposed to multiple infections. Credit: Sarah Reece & Sinclair Stammers, CC-BY

In malaria-endemic regions, humans are often infected repeatedly with the Plasmodium parasite, and the consequences of such multiple infections are under intense study. In contrast, little is known about possible co-infection and its consequences in the Anopheles mosquitoes that transmit the disease. A study published on July 16th in PLOS Pathogens reports that not only can individual mosquitoes accumulate infections from multiple blood feeds, but also that an existing malaria infection makes mosquitoes more susceptible to a second infection, and that infections reach higher densities when another strain is already present.

Interested in interactions between malaria parasites and their insect hosts, Laura Pollitt, from the University of Edinburgh, UK, and colleagues in the US, asked whether and how mosquitoes can be infected with different Plasmodium strains, how such heterogeneous parasites interact in the insects, and whether such interactions affect transmission of malaria to vertebrate hosts.

The researchers set up cages of female Anopheles mosquitoes and allowed them at defined times to feed on mice infected with two different Plasmodium strains. This study design allowed them to examine how the presence of a co-infecting strain affects parasites that enter the vector first and second, and to test whether co- impacts mosquito survival.

They found that mosquitoes can accumulate mixed strain malaria infections after feeding on multiple hosts, and found that parasites have a greater chance of establishing a secondary infection if another Plasmodium strain is already present in a mosquito. Moreover, the presence of the primary infection facilitated replication of the secondary infection while the first infection developed as normal. This resulted in doubly infected mosquitoes having substantially higher parasite loads.

The large parasite numbers do not appear to kill the insects, and as it is expected that mosquitoes carrying more parasites are more likely to transmit malaria to vertebrates, mosquitoes taking multiple infective bites might disproportionally contribute to malaria transmission. This in turn would increase rates of mixed infections in vertebrate (including human) hosts, with implications for the evolution of parasite virulence and the spread of drug-resistant strains.

"If the facilitation we have demonstrated here", the authors say, "occurs in natural transmission settings to humans, there could be significant epidemiological consequences. Control measures reducing prevalence in the vertebrate host, and therefore reducing the likelihood of mosquitoes taking multiple infective feeds, could disproportionally reduce transmission of individual strains. By increasing the proportion of infectious with mixed strain infections, it is also likely that the facilitation reported here will increase the rates of mixed infections in vertebrate hosts which could have implications for infection virulence and the spread of drug resistant strains."

Explore further: Wolbachia bacteria reduce parasite levels and kill the mosquito that spreads malaria

More information: Pollitt LC, Bram JT, Blanford S, Jones MJ, Read AF (2015) Existing Infection Facilitates Establishment and Density of Malaria Parasites in Their Mosquito Vector. PLoS Pathog 11(7):e1005003. DOI: 10.1371/journal.ppat.1005003

Related Stories

Wolbachia bacteria reduce parasite levels and kill the mosquito that spreads malaria

May 19, 2011
Wolbachia are bacteria that infect many insects, including mosquitoes. However, Wolbachia do not naturally infect Anopheles mosquitoes, which are the type that spreads malaria to humans. Researchers at the Johns Hopkins Bloomberg ...

Bacterial infection in mosquitoes renders them immune to malaria parasites

May 9, 2013
Scientists funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, have established an inheritable bacterial infection in malaria-transmitting Anopheles mosquitoes ...

A gut bacterium that attacks dengue and malaria pathogens and their mosquito vectors

October 23, 2014
Just like those of humans, insect guts are full of microbes, and the microbiota can influence the insect's ability to transmit diseases. A study published on October 23rd in PLOS Pathogens reports that a bacterium isolated ...

Control strategy for Dengue, malaria increases risk of West Nile virus

July 10, 2014
Mosquitoes infected with the bacteria Wolbachia are more likely to become infected with West Nile virus and more likely to transmit the virus to humans, according to a team of researchers.

Recommended for you

Pneumonia vaccine under development provides 'most comprehensive coverage' to date, alleviates antimicrobial concerns

October 20, 2017
In 2004, pneumonia killed more than 2 million children worldwide, according to the World Health Organization. By 2015, the number was less than 1 million.

Newly discovered viral marker could help predict flu severity in infected patients

October 20, 2017
Flu viruses contain defective genetic material that may activate the immune system in infected patients, and new research published in PLOS Pathogens suggests that lower levels of these molecules could increase flu severity.

H7N9 influenza is both lethal and transmissible in animal model for flu

October 19, 2017
In 2013, an influenza virus that had never before been detected began circulating among poultry in China. It caused several waves of human infection and in late 2016, the number of people to become sick from the H7N9 virus ...

Flu simulations suggest pandemics more likely in spring, early summer

October 19, 2017
New statistical simulations suggest that Northern Hemisphere flu pandemics are most likely to emerge in late spring or early summer at the tail end of the normal flu season, according to a new study published in PLOS Computational ...

New insights into herpes virus could inform vaccine development

October 18, 2017
A team of scientists has discovered new insights into the mechanisms of Epstein-Barr virus (EBV) infection, as well as two antibodies that block the virus' entry into cells. The findings, published in Proceedings of the National ...

Pair of discoveries illuminate new paths to flu and anthrax treatments

October 17, 2017
Two recent studies led by biologists at the University of California San Diego have set the research groundwork for new avenues to treat influenza and anthrax poisoning.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.