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Shining Light on Co-infection

13 January 2013

The infectious eggs inside the parasitic worm Heligmosomoides polygyrus

The infectious eggs inside the parasitic worm Heligmosomoides polygyrus

Infection with more than one parasite is common; termed co-infection. Co-infecting parasites are thought to interact with one another within individuals and can potentially alter the severity of the host symptoms, but investigating this has proved elusive due to difficulties in measuring infection loads. A study combining in vivo (whole animal) imaging with more traditional parasitological techniques has ‘shone light’ on coinfection and examined how coinfections interact within individuals.

Dr. Sarah Perkins, a new lecturer in Cardiff School of Biosciences whose work focuses on infectious disease dynamics, is using bioluminescent (glowing) bacteria to understand how pathogens grow during infection. Bioimaging, examining the growth of these glowing bacteria in a host, has opened up new opportunities to visualise infection within a host on a very fine time scale, which will ultimately allow researchers to fine-tune disease treatment programs.

Bioluminescent bacteria growing in culture

Bioluminescent bacteria growing in culture

In a recent study published in the Journal of the Royal Society Interface, Dr Perkins has shown that hosts that are co-infected with two different pathogens in distinct locations, (a bacteria in the lungs and a helminth (worm) in the gut), reach significantly higher bacterial loads early on in the infection process. The use of bioluminescent (glowing) bacteria and bioimaging allowed the research team to quantify the bacterial load every day and so capture dynamics that would otherwise have been missed in ‘traditional studies’. This new technique is considered an important step forward within the field. Furthermore, the co-infected individuals also produced significantly more infectious stages of the parasitic worm than singularly infected individuals.  In other words co-infected individuals become ‘super-infectious’. The discrete location of the two parasites within the host rules out any direct interaction between the co-infecting parasites and implies the interactions occurs through modification of the host immune system. More work is still required to understand exactly how this occurs but the observations made in this study have clear implications for disease control.

Dr. Sarah Perkins who led the research, said: “One of the major challenges in disease ecology is to predict which individuals are most infectious as these are the ones that may be driving epidemics. By using in vivo imaging we have shown that coinfection is a clear mechanism driving host infectiousness and seems to suggest that we should target disease control at co-infected individuals; a research focus of ours for the future.”

This work coincides with and compliments another recent study from the School of Biosciences, which examined co-infection within populations. Dr J. Lello and colleagues have shown at a population level, infection risk is substantially altered by co-infection, suggesting that 'smart control' which takes into account the potential interactions between parasite species and consideration of potential risk relationships, is essential. As such, targeting control at co-infected individuals will likely reduce the infectious output to the population. Both studies strongly suggest that co-infection must be considered when designing control programmes.

Dr Perkins’s research was funded by NSF grant no. EF-0520468 as part of the joint NSF-NIH-Ecology of Infectious Disease Programme and is published as open access in the Journal of the Royal Society Interface.

http://rsif.royalsocietypublishing.org/content/10/80/20120588