Endemic infection reduces transmission potential of an epidemic parasite during co-infection

Endemic, low-virulence parasitic infections are common in nature. Such infections may deplete host resources, which in turn could affect the reproduction of other parasites during co-infection. We aimed to determine whether the reproduction, and therefore transmission potential, of an epidemic parasite was limited by energy costs imposed on the host by an endemic infection. Total lipids, triacylglycerols (TAG) and polar lipids were measured in cockroaches (Blattella germanica) that were fed ad libitum, starved or infected with an endemic parasite, Gregarina blattarum. Reproductive output of an epidemic parasite, Steinernema carpocapsae, was then assessed by counting the number of infective stages emerging from these three host groups. We found both starvation and gregarine infection reduced cockroach lipids, mainly through depletion of TAG. Further, both starvation and G. blattarum infection resulted in reduced emergence of nematode transmission stages. This is, to our knowledge, the first study to demonstrate directly that host resource depletion caused by endemic infection could affect epidemic disease transmission. In view of the ubiquity of endemic infections in nature, future studies of epidemic transmission should take greater account of endemic co-infections.

Co-infections of malaria and soil-transmitted helminths in localities with different levels of urbanisation in the Mount Cameroon region

Malaria co-exists with intestinal helminths and they have different effects on infected individuals. A total of 235 and 208 children from Ekona and Great Soppo respectively of both sexes aged 4–14 years were enrolled into a cross-sectional study.Capillary blood was collected for detection and determination of malaria parasitaemia as well as PCV. Stool samples were collected for quantitative determination of helminth ova by Kato-Katz technique.The prevalence of malaria and helminths was higher in Ekona than Great Soppo. In Great Soppo, Trichuris was the most prevalent helminth than Great Soppo and an association was found between these co-infections. More children were co-infected in Ekona and co-infecting species were Ascaris and Plasmodium falciparum.The prevalence of malaria and intestinal helminths as well as co-infection was lower in Great Soppo than in Ekona, probably due to increased urbanization in Great Soppo than Ekona.

Functional group/guild modelling of inter-specific pathogen interactions: a potential tool for predicting the consequences of co-infection

Although co-infection is the norm in most human and animal populations, clinicians currently have no practical tool to assist them in choosing the best treatment strategy for such patients. Given the vast range of potential pathogens which may co-infect the host, obtaining such a practical tool may seem an intractable problem. In ecology the joint concepts of functional groups and guilds have been used to conceptually simplify complex ecosystems, in order to understand how their component parts interact and may be manipulated. Here we propose a mechanism by which to apply these concepts to pathogen co-infection systems. Further, we describe how these groups could be incorporated into a mathematical modelling framework which, after validation, could be used as a clinical tool to predict the outcome of any particular combination of pathogens co-infecting a host.

Pathogen responses to host immunity: the impact of time delays and memory on the evolution of virulence

Current analytical models of the mammalian immune system typically assume a specialist predator-prey relationship between invading pathogens and the active components of the immune response. However, in reality, the specific immune system is not immediately effective following invasion by a novel pathogen. First, there may be an explicit time delay between infection and immune initiation and, second, there may be a gradual build-up in immune efficacy (for instance, during the period of B-cell affinity maturation) during which the immune response develops, before reaching maximal specificity to the pathogen. Here, we use a novel theoretical approach to show that these processes, together with the presence of long-lived immune memory, decouple the immune response from current pathogen levels, greatly changing the dynamics of the pathogen-immune system interaction and the ability of the immune response to eliminate the pathogen. Furthermore, we use this model to show how distributed primary immune responses combine with immune memory to greatly affect the optimal virulence of the pathogen, potentially resulting in the evolution of highly virulent pathogens.

The effect of single and concomitant pathogen infections on condition and fecundity of the wild rabbit (Oryctolagus cuniculus)

We assessed the effect of two pathogens (myxoma virus and Eimeria stiedae) and five macroparasites (gastrointestinal helminth species) of the wild rabbit (Oryctolagus cuniculus) upon total host body mass and abdominal fat level. Additionally, we assessed the effects of these organisms on the number of foetuses in adult females during the peak breeding period. Both mass of abdominal fat and total body mass of the rabbit were negatively associated with myxoma virus infection and increasing helminth species richness. Total body mass was also negatively associated with the protozoan parasite E. steidae. No relationship was found between any of the parasites/pathogens and the number of foetuses in adult females, although only relatively small sample sizes were available for this section of the analysis. Increasing host body mass was positively associated with number of foetuses and we propose that mass reduction caused by the pathogen and parasite species could also have the consequence of reducing foetal number.

New world origins for haemoparasites infecting United Kingdom grey squirrels (Sciurus carolinensis), as revealed by phylogenetic analysis of bartonella infecting squirrel populations in England and the United States

Phylogenetic analyses of bartonella have suggested divergence between bartonellae that infect mammals native to the Old and New Worlds. We characterized bartonella isolated from Eastern grey squirrels (Sciurius carolinensis) in the United States and from grey and red squirrels (Sciurus vulgaris) in the United Kingdom by nucleotide sequence comparison (gltA and groEL). Isolates from grey squirrels in the United States and the United Kingdom were identical, and most similar to Bartonella vinsonii, a species associated with New World rodents. A single and novel bartonella genotype was obtained from all 12 red squirrel isolates. Although grey squirrels were first introduced into the United Kingdom over 125 years ago, they continue to be infected solely by the bartonella associated with grey squirrels native to the United States. These results illustrate that exotic species may be accompanied by the introduction and maintenance, over many generations, of their microparasites.

Patterns of parasite aggregation in the wild European rabbit (Oryctolagus cuniculus)

Understanding the factors controlling the distribution of parasites within their host population is fundamental to the wider understanding of parasite epidemiology and ecology. To explore changes in parasite aggregation, Taylor's power law was used to examine the distributions of five gut helminths of the wild rabbit. Aggregation was found to be a dynamic process that varied with year, season, host sex, age class, and myxomatosis. Yearly and seasonal changes are thought, in the main, to be the result of variations in weather conditions acting upon infectious stages (or intermediate hosts). Evidence in support of this was the comparatively low degree of fluctuation in the aggregation of the pinworm, Passalurus ambiguus, as the infectious stage of this parasite is likely to be less susceptible to environmental variation. Host age had a marked effect on the level of aggregation of all parasites, but this effect varied between parasite species. P. ambiguus, Trichostrongylus retortaeformis and Cittotaenia denticulata aggregation were lower in adult than juvenile rabbits whilst Graphidium strigosum and Mosgovoyia pectinata aggregation tended to increase with age. Host immunity is thought to be responsible for these differences. Differences in aggregation for different parasites were also seen when the rabbit population was split into males and females. Myxomatosis had a marked effect on helminth distribution with substantially less aggregation in rabbits showing clinical signs of the disease.

The impact of acne: a study of adolescents' attitudes, perception and knowledge

AIM

To assess adolescent students' attitudes to, perceptions and knowledge of acne and to assess the effect of acne on daily living.

METHOD

Students from Auckland sixth and seventh form classes were selected from ten Auckland secondary schools using a randomisation process which ensured proportional representation by socioeconomic group and gender. Eight hundred and forty-seven students completed a written questionnaire on the subject of acne vulgaris and had their acne examined. Their acne was graded using a modification of the Leeds system which determines severity on the basis of number, extent and nature of the skin lesions.

RESULTS

Acne was present in 91% of males and 79% of females. Students' perceptions of the severity of their acne were significantly related to objective clinical assessment (p=0.00001). Severity of acne determined the extent of embarrassment (p<0.00001) and the lack of enjoyment of and participation in social activities (p<0.00002). These analyses were significant for both males and females. Students had misconceptions regarding the causes of acne. Parental occupation and ethnic group were related to knowledge of treatment for acne.

CONCLUSION

Acne causes personal and social difficulties for a large number of adolescent students. There is a need for all students to have access to appropriate information and health services so that the social and psychological consequences of acne are minimised.

Prevalence of acne vulgaris in Auckland senior high school students

AIM

To assess the prevalence and severity of acne vulgaris in adolescent students.

METHOD

867 students in Auckland sixth and seventh form classes were interviewed on the subject of acne vulgaris. Of these 847 students were examined and graded for severity of their acne using a modification of the Leeds technique which ranks severity according to number, extent and nature of the acne lesion.

RESULTS

Ninety-one percent of males and 79% of females had some acne. Severe acne was present in 6.9% males and 1.1% females. Severe and moderately severe acne was significantly more common in males (OR = 2.6 95% Cl 1.73 < OR < 3.9). In the univariate analysis there was no association of moderately severe and severe acne with parental occupational group nor ethnicity.

CONCLUSION

Moderate and severe acne is a common finding in Auckland senior high school classes with males being more affected than females.