Rodents as Hosts of Pathogens and Related Zoonotic Disease Risk

Rodents are known to be reservoir hosts for at least 60 zoonotic diseases and are known to play an important role in their transmission and spread in different ways. We sampled different rodent communities within and around human settlements in Northern Senegal, an area subjected to major environmental transformations associated with global changes. Herein, we conducted an epidemiological study on their bacterial communities. One hundred and seventy-one (171) invasive and native rodents were captured, 50 from outdoor trapping sites and 121 rodents from indoor habitats, consisting of five species. The DNA of thirteen pathogens was successfully screened on the rodents’ spleens. We found: 2.3% of spleens positive to Piroplasmida and amplified one which gave a potentially new species Candidatus “Theileria senegalensis”; 9.35% of Bartonella spp. and amplified 10, giving three genotypes; 3.5% of filariasis species; 18.12% of Anaplasmataceae species and amplified only 5, giving a new potential species Candidatus “Ehrlichia senegalensis”; 2.33% of Hepatozoon spp.; 3.5% of Kinetoplastidae spp.; and 15.2% of Borrelia spp. and amplified 8 belonging all to Borrelia crocidurae. Some of the species of pathogens carried by the rodents of our studied area may be unknown because most of those we have identified are new species. In one bacterial taxon, Anaplasma, a positive correlation between host body mass and infection was found. Overall, male and invasive rodents appeared less infected than female and native ones, respectively.

Rodents as Hosts of Pathogens and Related Zoonotic Disease Risk

Rodents are known to be reservoir hosts for at least 60 zoonotic diseases and are known to play an important role in their transmission and spreading in different ways. We sampled different rodent communities within and around human settlements in Northern Senegal, an area subjected to major environmental transformations associated with global changes. Herein, we conducted an epidemiological study on their bacterial communities.One hundred and seventy-one (171) invasive and native rodents were captured, 50 from outdoors trapping sites and 121 rodents from indoors habitats, consisting on 5 species. DNA of thirteen pathogens have been successfully screened on the rodent’s spleens. We found: 2.3% of positive spleens to Piroplasmida and amplified one which gives a potentially new species Candidatus “Theileria senegalensis”; 9.35% of Bartonella spp. and amplified 10, giving three genotypes. 3.5% of filariasis species; 18.12% of Anaplasmataceae species and amplified only 5, giving a new potential species Candidatus “Ehrlichia senegalensis”; 2.33 % of Hepatozoon spp.; 3.5% of Kinetoplastidae spp; and 15.2% of Borrelia spp. and amplified 8 belonging all to Borrelia crocidurae.Some of the species of pathogens carried by the rodents of our studied area may be unknown because most of those we have identified are new species. In one bacterial taxon, Anaplasma, a positive correlation between host body mass and infection was found. Overall, male and invasive rodents appeared less infected than female and native ones, respectively.

The human gut bacteria Christensenellaceae are widespread, heritable, and associated with health

The Christensenellaceae, a recently described family in the phylum Firmicutes, is emerging as an important player in human health. The relative abundance of Christensenellaceae in the human gut is inversely related to host body mass index (BMI) in different populations and multiple studies, making its relationship with BMI the most robust and reproducible link between the microbial ecology of the human gut and metabolic disease reported to date. The family is also related to a healthy status in a number of other different disease contexts, including obesity and inflammatory bowel disease. In addition, Christensenellaceae is highly heritable across multiple populations, although specific human genes underlying its heritability have so far been elusive. Further research into the microbial ecology and metabolism of these bacteria should reveal mechanistic underpinnings of their host-health associations and enable their development as therapeutics.

Host body size and the abundance of chewing lice (Phthiraptera: Amblycera, Ischnocera) infesting eight owl species (Aves: Strigiformes) in Manitoba, Canada

Specimens (n = 508) of eight species of owl (Aves: Strigiformes) collected from 1994 to 2017 in Manitoba, Canada, were weighed and examined for chewing lice (Phthiraptera: Amblycera, Ischnocera). The relationship between host body mass and infestation by 12 species of lice was examined. Host body mass explained 52% (P = 0.03) of the variation in mean intensity of louse infestation among hosts, due primarily to a high abundance of lice on the heaviest owl species. The relationship was due to the mean intensity of lice, and neither species richness nor the prevalence of lice was related to host body mass. For individual louse species, the relationship was due primarily to Kurodaia acadicae Price and Beer, Kurodaia magna Emerson, and an undetermined species of Kurodaia Uchida (Phthiraptera: Menoponidae) (R2 = 0.997), but not the nine Strigiphilus Mjöberg (Phthiraptera: Philopteridae) species (R2 = 0.27). Louse intensity did not increase with body size for individual birds of any of the owl species. Mean intensity is expected to increase in proportion with the size, specifically the surface area, of the host. Why that relationship holds only for one louse genus, and not for the most abundant genus of lice on owls, and weakly compared with other families of birds, has yet to be determined.

Abundance of chewing lice (Phthiraptera: Amblycera and Ischnocera) increases with the body size of their host woodpeckers and sapsuckers (Aves: Piciformes: Picidae)

Specimens of five species of woodpeckers (Piciformes: Picidae) from Manitoba, Canada, were weighed and examined for chewing lice, 1998–2015: downy woodpecker (Picoides pubescens (Linnaeus), n=49), hairy woodpecker (Picoides villosus (Linnaeus), n=23), pileated woodpecker (Dryocopus pileatus (Linnaeus), n=10), northern flicker (Colaptes auratus (Linnaeus), n=170), and yellow-bellied sapsucker (Sphyrapicus varius (Linnaeus), n=239). The relationship between body mass of each host species and infestation by seven species of lice was analysed: Menacanthus pici (Denny) from all host species, Brueelia straminea (Denny) from Picoides Lacépède species, Penenirmus jungens (Kellogg) from northern flicker, Penenirmus auritus (Scopoli) from the other four hosts, Picicola porisma Dalgleish from northern flicker, Picicola snodgrassi (Kellogg) from Picoides species, and Picicola marginatulus (Harrison) from pileated woodpeckers. Mean abundance of lice increased with the mean mass of their host. Neither the species richness of lice nor the prevalence of lice were related to host body mass. Host body mass explained 98% of the variation in mean intensity of louse infestation among hosts. The positive association of mean intensity and body size was also detected for three genera of lice. Louse intensity also increased with body size for individual birds, more so for some species of lice and hosts than others. Body size matters, but the adaptations that allow higher mean intensity on larger host species remain to be determined.

Ectoparasites of small-mammals: determinants of community structure in South American savannah

SUMMARYThis study aimed to assess the contribution of hosts characteristics (rodents and marsupials) in the organization of ectoparasite communities present in woodland patches in western central Brazil. We verified the effect of host species, sex, body mass and vertical strata in addition to the role of seasonality on the ectoparasite composition, richness and abundance. The total sampling effort was 22 032 trap-nights equally distributed in 54 woodland patches. Variance partition and principal coordinate analysis were used to verify the existence of significant relationships between response variables and predictors. As expected, host species was the most important variable in ectoparasite community assembly. The composition, richness and abundance of mites and lice were highly influenced by host species, although higher for mites than for lice. Host body mass had a determining role on the richness and abundance of tick species. Vertical stratification and seasonality had weak influence, while the sex of the host had no influence on the organization of these communities. The results are closely related to the evolutionary characteristics of the species involved, as well as with local environmental characteristics of the study area.

Fecundity compensation and fecundity reduction among populations of the three-spined stickleback infected by Schistocephalus solidus in Alaska

SUMMARYWe surveyed nine populations of the three-spined stickleback infected by the diphyllobothriidean cestode Schistocephalus solidus from south-central Alaska for two apparent forms of tolerance to infection in females capable of producing egg clutches notwithstanding large parasite burdens. Seven populations exhibited fecundity reduction, whereas two populations showed fecundity compensation. Our data suggest that fecundity reduction, a side effect resulting from nutrient theft, occurs in two phases of host response influenced by the parasite : host body mass (BM) ratio. The first is significantly reduced ovum mass without significant reduction in clutch size, and the second one involves significant reductions in both ovum mass and clutch size. Thus, ovum mass of host females who are functionally being starved through nutrient theft seems to be more readily influenced by parasitism and, therefore, decreased before clutch size is reduced. This inference is consistent with expectations based on the biology of and effect of feeding ration on reproduction in stickleback females. Fecundity compensation appears to be uncommon among populations of three-spined stickleback in Alaska and rare among populations throughout the northern hemisphere. Fecundity reduction seems to be common, at least among stickleback populations in Alaska.

Competition, virulence, host body mass and the diversification of macro-parasites

Adaptive speciation has been much debated in recent years, with a strong emphasis on how competition can lead to the diversification of ecological and sexual traits. Surprisingly, little attention has been paid to this evolutionary process to explain intrahost diversification of parasites. We expanded the theory of competitive speciation to look at the effect of key features of the parasite lifestyle, namely fragmentation, aggregation and virulence, on the conditions and rate of sympatric speciation under the standard ‘pleiotropic scenario’. The conditions for competitive speciation were found similar to those for non-parasite species, but not the rate of diversification. Adaptive evolution proceeds faster in highly fragmented parasite populations and for weakly aggregated and virulent parasites. Combining these theoretical results with standard empirical allometric relationships, we showed that parasite diversification can be faster in host species of intermediate body mass. The increase in parasite load with body mass, indeed, fuels evolution by increasing mutants production, but because of the deleterious effect of virulence, it simultaneously weakens selection for resource specialization. Those two antagonistic effects lead to optimal parasite burden and host body mass for diversification. Data on the diversity of fishes' gills parasites were found consistent with the existence of such optimum.

Positive co-occurrence of flea infestation at a low biological cost in two rodent hosts in the Canary archipelago

SUMMARYNon-random assemblages have been described as a common pattern of flea co-occurrence across mainland host species. However, to date, patterns of flea co-occurrence on islands are unknown. The present work investigates, on one hand, whether the decrease in the number of species on islands affects the pattern of flea co-occurrence, and on the other hand, how the cost of higher flea burdens affects host body mass. The study was carried out in the Canary Islands (Spain) using null models to analyse flea co-occurrence on Rattus rattus and Mus musculus. Results supported aggregation of flea species in Mus but not in Rattus, probably due to the relationship between abundance and both prevalence and intensity of infection of the main flea species parasitizing Mus. In addition, heavy individuals of both rodent species showed the highest flea burdens as well as higher species richness, probably due to the continued accumulation of fleas throughout life and/or immunological resistance mechanisms. Whatever the mechanisms involved, it is clear that co-occurrence and high parasite intensities do not imply a detrimental biological cost for the rodents of the Canary Islands.