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Miss Joanna Rumsey 


Supervisors: Dr Joanne Lello & Dr Joanne Cable (Cardiff University)
Blattella germanica

Figure 1 Blattella germanica

I am interested in the epidemiology of disease and especially how multiple infections can influence the way that diseases transmit through a population and how multiple infections can alter both host and pathogen life-history strategies. This is particularly relevant as most emerging and re-emerging infectious diseases originate from developing regions, where people commonly have other endemic infections. However, the study of microparasitic infections has largely neglected the presence of these common endemic parasites, and this may limit the usefulness of models used to track and control infectious diseases.

Gregarina blattarum

Figure 2 Gregarina blattarum

The laboratory model I am using during my PhD, comprises one host species, the German cockroach, Blattella germanica (Fig. 1), a well-studied organism that is susceptible to many different types of infection. A common parasite of this host is Gregarina blattarum (Fig. 2), a gastrointestinal protozoan that resides in the cockroach mid-gut and which we have used as a model for macroparasitic infection due to high low pathogenicity and production of infective stages that are transmitted via the production of spores outside of the host.

The second parasite is the entomopathogenic nematode Steinernema carpocapsae (Fig. 3). This species is in use as a biological control agent due to its high virulence, and hence we have used it in the system to represent a microparasite as it completes its entire life cycle within the host, and infective stages are transmitted only via contact with an infected host cadaver or patch of ground immediately surrounding it.

Steinernema carpocapsae

Figure 3 Steinernema carpocapsae

I have so far monitored the dynamics of singly infected cockroach populations, using a mark-recapture technique that was developed in my first year. I have also determined the life history of hosts infected with G. blattarum and found variations between fecundity and survivorship during infection. During initial coinfection studies I have found that hosts that are infected with G. blattarum, correspond to reduced nematode reproduction during coinfection, but aim to determine the overall dynamics of this system of host populations during infection with both pathogens. This work will also be extended to determine the outcomes of coinfection on host mortality and parasite transmission.

In summary, hosts commonly have multiple infections that are likely to affect disease virulence and host population dynamics differently compared to single infections. Given that most work to date has focused on single infections, this novel multi-parasite-host system will provide important epidemiological evidence for an improved insight into parasite ecology. 

Collaborators

Dr Sheena Cotter, Oxford University: Invertebrate immunity

Dr Mark Jervis, Cardiff University: Host life history and energy reserves

Dr Mike Bonsall, Oxford University: Time series analysis