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opencc-zeroMar 2024View details →

The impact of within-host coinfection interactions on between-host parasite transmission dynamics varies with spatial scale

Within-host interactions among coinfecting parasites can have major consequences for individual infection risk and disease severity. However, the impact of these within-host interactions on between-host parasite transmission, and the spatial scales over which they occur, remain unknown. We developed and applied a novel spatially explicit analysis to parasite infection data from a wild wood mouse (Apodemus sylvaticus) population. We previously demonstrated a strong within-host negative interaction between two wood mouse gastrointestinal parasites, the nematode Heligmosomoides polygyrus, and the coccidian Eimeria hungaryensis, using drug-treatment experiments. Here, we show this negative within-host interaction can significantly alter the between-host transmission dynamics of E. hungaryensis, but only within spatially-restricted neighbourhoods around each host. However, for the closely related species E. apionodes, which experiments show does not interact strongly with H. polygyrus, we did not find any effect on transmission over any spatial scale. Our results demonstrate that the effects of within-host coinfection interactions can ripple out beyond each host to alter the transmission dynamics of the parasites, but only over local scales that likely reflect the spatial dimension of transmission. Hence there may be knock-on consequences of drug treatments impacting the transmission of non-target parasites, altering infection risks even for non-treated individuals in the wider neighbourhood.

Fig. 1 in Equal contributions of feline immunodeficiency virus and coinfections to morbidity in African lions

Fig. 1. FIV infection is common in lions of Kruger National Park. Within the sample population, 72.8% (142/195) of lions were infected with FIV. Prevalence of FIV infection was similar between males and females (75.6% versus 70.2%; n = 74 and 121, respectively), but increased with host age (a). For ease of visualization, age has been broken up by life stage into cubs (0–2yrs), subadults (2.1–4yrs), young adults (4.1–6yrs), prime adults (6.1–8yrs), and seniors (>8yrs) based on previous age classifications (Schaller, 1976). Regional prevalence of FIV was highest in the central region and lowest in the north (b). The map to the right shows locations where lion prides were sampled.

Fig. 4 in Equal contributions of feline immunodeficiency virus and coinfections to morbidity in African lions

Fig. 4. FIV has strong direct and indirect effects on overall health. The final path model (a) shows only statistically significant relationships between manifest variables (rectangles) and latent variables (circles) for FIV infection, immune response (IMM), coinfections with hemoparasites (Hemoparasites), co-infections with gastrointestinal parasites (Helminths), and morbidity (Morbidity). Note that the parameter βx,z between each variable of interest represents the path coefficient obtained from least squares regression examining the relationship between one latent variable and the next (for example, FIV to IMM). Blue arrows represent positive relationships, whereas red arrows denote negative relationships. Final sample size was 106 lions.

Fig. 3 in Equal contributions of feline immunodeficiency virus and coinfections to morbidity in African lions

Fig. 3. FIV significantly increases the prevalence of select gastrointestinal and hemoparasitic coinfections, as well as overall parasite richness for both groups. Graph (a) shows the prevalence of coinfecting parasites isolated in lions from this study. Sample size for the parasite groups included is as follows: n = 114 for gastrointestinal parasites; n = 190 for hemoparasites; and n = 195 for viral parasites. Coinfections are broken down by FIV status (positive versus negative). The two additional graphs illustrate the relationship between FIV status and gastrointestinal parasite richness (b) and hemoparasite richness (c).

Fig. 2 in Equal contributions of feline immunodeficiency virus and coinfections to morbidity in African lions

Fig. 2. FIV has broad effects on lion health and is associated with progressive immune impairment. Box (2a) above provides a complete list of the health metrics measured for the purposes of this study. Arrows to the right of each variable summarize the directionality of statistically significant changes with FIV infection. Descriptive statistics and reference values can be found in Table 2. Complete model output can be found in supplementary tables S1–S4. For ease of visualization, each parameter has been broken into categories of clinical relevance. To the right, age-related changes in lymphocyte profiles are shown for total lymphocyte counts in FIV-positive versus FIV-negative lions (b); as well as specific lymphocyte subsets in FIV-positive lions (c). Due to small sample size for lymphocyte subsets, subadults, and cubs have been included together under the 'juvenile' category.

opencc-zeroMay 2023View details →

Multispecies coinfections and presence of antibiotics shape resistance and fitness costs in a pathogenic bacterium

Increasing antimicrobial resistance (AMR) poses a challenge for treatment of bacterial diseases. In real life, bacterial infections are typically embedded within complex multispecies communities and influenced by the environment, which can shape costs and benefits of AMR. However, knowledge of such interactions and their implications for AMR in vivo is limited. To address this knowledge gap, we investigated fitness-related traits of a pathogenic bacterium (Flavobacterium columnare) in its fish host, capturing the effects of bacterial antibiotic resistance, multispecies coinfections (metazoan fluke Diplostomum pseudospathaceum), and antibiotic exposure. We quantified real-time replication and virulence of sensitive and resistant bacteria and demonstrate that both bacteria can benefit from coinfection in terms of persistence and replication, depending on the coinfecting partner and antibiotic presence. We also show that antibiotics can benefit resistant bacteria by increasing bacterial replication under coinfection with flukes. These results emphasize the importance of diverse, inter-kingdom coinfection interactions and antibiotic exposure in shaping costs and benefits of AMR, supporting their role as significant contributors to the spread and long-term persistence of resistance.

opencc-zeroJun 2023View details →

Data for: Age structure eliminates the impact of coinfection on epidemic dynamics in a freshwater zooplankton system

Parasites often coinfect host populations, and, by interacting within hosts, might change the trajectory of multi-parasite epidemics. However, host-parasite interactions often change with host age, raising the possibility that within-host interactions between parasites might also change, influencing the spread of disease. We measured how heterospecific parasites interacted within zooplankton hosts and how host age changed these interactions. We then parameterized an epidemiological model to explore how age-effects altered the impact of coinfection on epidemic dynamics. In our model, we found that in populations where epidemiologically relevant parameters did not change with age, the presence of a second parasite altered epidemic dynamics. In contrast, when parameters varied with host age (based on our empirical measures), there was no longer a difference in epidemic dynamics between singly and coinfected populations, indicating that variable age structure within a population eliminates the impact of coinfection on epidemic dynamics. Moreover, infection prevalence of both parasites was lower in populations where epidemiologically relevant parameters changed with age. Given that host-population age structure changes over time and space, these results indicate that age-effects are important for understanding epidemiological processes in coinfected systems and that studies focused on a single age group could yield inaccurate insights.