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Host species richness and parasite species richness are often positively correlated, but the strength of this relationship varies from study to study. What accounts for this variability? Here, we explore the role of spatial scale in mediating the commonly reported positive relationship between host and parasite diversity. Building from ecological theory, we lay out a series of hypotheses for how spatial grain size might influence both the strength and slope of this relationship. Most significantly, we consider how variability in spatial grain size may result in differences in sampling effort that affect estimates of host and parasite richness differently, and we explore the potential for spatial grain to have divergent effects on strength versus slope of the relationship between host and parasite richness. Finally, we examine what empirical data exist to test the outlined hypotheses and conduct a meta-regression of published studies. Our analyses—which detected no significant associations—highlight several factors that compromise our ability to robustly compare the host–parasite richness relationship across contexts, including mismatches between absolute spatial scale and spatial scale of ecological processes as well as variability across and within studies with respect to spatial grain size, taxonomic resolution, definitions of “hosts” and “parasites,” and sampling effort. This work suggests that questions regarding the spatial dependence of the host diversity–parasite diversity relationship may be most-effectively addressed within a single multi-host–multi-parasite system.
The lancet fluke, Dicrocoelium dendriticum, is perhaps the best-known example of parasite manipulation of host behavior, which is manifested by a radically changed behavior that leaves infected ants attached to vegetation at times when transmission to an herbivore host is optimal. Despite the publicity surrounding this parasite, curiously little is known about factors inducing and maintaining behavioral changes in its ant intermediate host. This study examined the importance of 3 environmental factors on the clinging behavior of red wood ants, Formica polyctena, infected with D. dendriticum. This behavior, hypothesized to involve cramping of the mandibular muscles in a state of tetany, was observed in naturally infected F. polyctena under controlled temperature, light, and humidity conditions. We found that low temperature significantly stimulated and maintained tetany in infected ants while light, humidity, ant size, and infection intensity had no influence on this behavior. Under none of the experimental conditions did uninfected ants attach to vegetation, demonstrating that tetany was induced by D. dendriticum. Temperature likely has a direct impact on the initiation of clinging behavior, but it may also serve as a simple but reliable indicator of the encounter rate between infected ants and ruminant definitive hosts. In addition, temperature-sensitive behavior manipulation may protect infected ants from exposure to temperatures in the upper thermal range of the host.
Pakistan faces critical challenges pertaining to cutaneous leishmaniasis (CL), where it's distribution is more or less patchy. The goal of this study was to assess the incidence of CL as well as to identify potential risk factors in Peshawar region, Khyber Pakhtunkhwa, Pakistan. The study was conducted in the dermatology outpatient unit at Kuwait Teaching Hospital, Peshawar, Khyber Pakhtunkhwa, Pakistan. Longitudinal out-patient department visit data for 9,631 CL patients spanning a 42-mo (April 2011–October 2014) period was analyzed using autoregressive integrated moving average (ARIMA) time series models ARIMA(1,0,0)(0,1,0)12 and ARIMA(0,0,0)(0,1,0)12. The ARIMA concluded that the number of patients was increasing over time. Over the duration, frequency of male patients (58.2%) was higher. The mean age of CL patients was 16.4 (confidence interval = 16.14–16.70) yr and the majority of the patients were aged 5–20 yr (52.6%). Inflow of CL patients peaked close to February and March, followed by a decline until its lowest point in the months of August and September (P < 0.001). Two hundred individuals, including 88 cases and 112 controls, were matched by gender and age categories (<5, 5–20, >20 yr) to derive 63 matched pairs. Using univariate conditional logistic regression analyses of the matched pairs, we found that living in congested rooms (>6 persons), having family members with lesions (active/scars), keeping cattle inside dwellings at night, and having in-door vegetation were established as factors that significantly increased the risk of CL. On the other hand, living in houses constructed with bricked walls or wooden roofs (thatched/beam), ownership of treated bed nets, and having meshed windows were proven to be protective against CL. It was evident that the disease incidence has been on a gradual rise over the past few years. It was concluded that household clustering, house construction, and conventional behavioral practices (living with cattle) greatly impact the epidemiology of CL in the region. Conclusions from this study have significant implications for prospective control programs.
Spatial distribution and seasonal variation in mean intensity and prevalence of monogeneans on the gills of grass carp (Ctenopharyngodon idellus) were investigated from September 2012 to December 2014 in a fish pond in Wuhan, China. During this period, 2 species of Dactylogyrus were found, i.e., Dactylogyrus lamellatus and Dactylogyrus ctenopharyngodonis. Dactylogyrus lamellatus was present during the entire duration of the investigation, whereas D. ctenopharyngodonis was only detected after January 2014, when another batch of grass carp fingerlings was added to the pond. Prevalence of the 2 Dactylogyrus spp. was relatively high throughout the year, but significant seasonal changes were detected in the mean intensity of the 2 species (P < 0.05). Mean intensity of D. lamellatus peaked in late winter and spring, and then dropped to the lowest point in summer. Dactylogyrus ctenopharyngodonis exhibited a high mean intensity in summer and autumn, but low in winter and spring. Spatial distribution of the 2 species was similar: the highest mean intensity was found on medial and distal parts of the second gill arch. Moreover, no evident change was detected in niche preference of D. lamellatus after the infection of D. ctenopharyngodonis occurred. There was no significant positive correlation in abundance between the 2 species (P > 0.05). In addition, there were no significant differences in the percentage of mean intensity of the 2 species on each gill arch among low-, medium-, and high-intensity groups (P > 0.05). These results suggest unsaturated gill niches and the absence of interspecific competition between the 2 Dactylogyrus species.
A new species of flea of the genus Cleopsylla Rothschild, 1914 (Siphonaptera: Stephanocircidae) is described from sigmodontine rodents from northwestern Argentina. In Argentina, the genus was cited for the first time in 2008, but the species was erroneously identified. An identification key to species of Cleopsylla is presented.
The edible land snail Cornu aspersum (Pulmonata: Stylommatophora) acts as second intermediate host in the cycle of Brachylaima sp. trematode, harboring free metacercariae in its kidney. The ingestion of undercooked infected snails by humans allows metacercariae to develop to adult stage in the intestine, causing brachylaimiasis. Praziquantel (PZQ) is the drug of choice to treat trematodiasis and it is effective against Brachylaima sp. metacercariae. The objective of this work was to assess, by transmission electron microscopy (TEM), the ultrastructural changes produced on the tegument and gastrodermis of the Brachylaima metacercariae recovered from C. aspersum treated with PZQ in comparison with untreated ones. Snails naturally infected by Brachylaima sp. metacercariae were treated by PZQ both individually and in groups. Metacercariae recovered from treated and control snails were processed for TEM. The tegument of untreated metacercariae was covered by a regular and thick glycocalyx. The syncytial epithelium contained abundant T2 secretory bodies appearing as membrane-bound biconcave disk-vesicles with high electron-dense and uniform content. The T2 secretory bodies located along the external area of the syncytium were mainly arranged at right angles to the apical plasma membrane. In treated metacercariae, the content of the T2 secretory bodies appeared altered, degenerating from high to low electron density, losing its uniform appearance and forming high electron-dense accumulations scattered around the periphery of the vesicle and separated by low electron-dense spaces. The presence of clusters was detectable in the central area. The characteristic arrangement of the T2 secretory bodies observed in untreated metacercariae was lost in treated ones. Vesicles near the apical area of the tegument no longer maintained their arrangement perpendicular to the apical plasma membrane. The characteristic arrangement of T2 secretory bodies and mitochondria was lost. The T2 secretory bodies were also found altered in the tegumental cell bodies, suggesting that the alterations started at the production stage. Mitochondria were severely degenerated and located in the apical area of the tegument. The digestive system displayed a strong contraction, which included the disappearance of the intracecal lumen.
This study was undertaken to assess the damage caused by Pomphorhynchus bulbocolli to Catostomus commersoni (white sucker). Three specimens of C. commersoni were collected during early September 2014 via gill net from Canadarago Lake (Otsego County, New York), then dissected and examined for intestinal parasites. One C. commersoni, collected from a tributary of Otsego Lake (Otsego County, New York), was used as a control in this study because it was not infected with intestinal helminths. Upon dissection, damage to the fish intestine was macroscopically visible, with the intestine perforated when infected with P. bulbocolli. Intestines observed to be infected with P. bulbocolli were opened with a longitudinal incision and fixed in neutral buffered formalin with the acanthocephalans remaining attached. Histological sections of intestine with P. bulbocolli attached were compared with histological sections of intestine in which no worms were present. Examination of sections revealed full penetration of the intestinal wall and tissue destruction to the mucosa, submucosa, stratum compactum, and circular and longitudinal muscle layers, as well as an extensive host immune response in the form of proliferation of cells at the sites of wounds. While these results were consistent with previous histopathological studies on this host and parasite species, the occurrence of pockets of hyaline degeneration in the muscularis reported here is a new finding for this host–parasite system, and it appears to be quite rare in the parasitological literature. It is hypothesized that the presence of hyaline degeneration may be related to secretion of trypsinlike proteins from the presoma of the acanthocephalan, a phenomenon suggested previously for the congener Pomphorhynchus laevis. The host–parasite interaction involving physical damage, secretion of enzymes, and an extensive host immune response may be the cause of the damage, but further research is needed to investigate the nature of these interactions.
Wild rodents such as Peromyscus spp. are intermediate hosts for the zoonotic ascarid Baylisascaris procyonis (raccoon roundworm), and previous studies indicate Peromyscus leucopus (white-footed mouse) likely serves an important role in parasite ecology. Natural infections have been sporadically identified in a few Peromyscus spp., but no data are available on differences in susceptibility among the many other species. We compared survival and infection dynamics of B. procyonis in 4 species (P. leucopus, Peromyscus maniculatus [deer mouse], Peromyscus californicus [California mouse], Peromyscus polionotus [Oldfield mouse]) from regions of varying habitat types as well as B. procyonis prevalence in raccoons. Six captive-bred mice of each species were inoculated per os with 1 of 3 biologically-relevant doses of embryonated B. procyonis eggs (∼10, ∼50, or ∼500). Animals were monitored twice daily for clinical signs and behavioral abnormalities and were euthanized at the onset of neurological signs or extensive (≥20%) weight loss, or at 45 days post-infection if no disease developed. Larvae were counted in the brain via microscopic examination and in skeletal muscle and visceral organs via artificial digestion. In the high-dose group, all but 1 mouse developed severe neurologic disease and were euthanized. In the medium-dose group, survival was variable and ranged from 33–85% across species. Little to no disease was observed in the low-dose group, although 1 P. maniculatus developed disease and was euthanized. Survival analysis reveals P. leucopus had a longer time until clinical disease onset versus the other species, which did not differ significantly from each other. Interestingly, larval recovery relative to dose was nearly identical across species and doses; however, larvae were differentially distributed in skeletal muscle, visceral organs, and brain among species. These data indicate that P. leucopus may be more resilient toward severe baylisascariasis compared to the other species and that even closely-related rodents may experience differential mortality. This variation in tolerance may have ecological implications for the different species as B. procyonis intermediate hosts, although more work is needed to put these experimental findings into context.
Cattle are intermediate hosts for 2 zoonotic species of Sarcocystis, Sarcocystis hominis and Sarcocystis heydorni. Here we report S. heydorni from cattle for the first time in China. Sarcocysts of S. heydorni were found in muscle from 173 of 1,630 (10.6%) cattle in abattoirs (9.7% in skeletal muscles, 3.4% esophagus, 2.5% diaphragm, and 0.1% tongue; heart muscle was negative). By means of light microscopy, S. heydorni sarcocysts were thin-walled (<1 μm). Using transmission electron microscopy, the sarcocyst wall had short (0.3–0.5 × 0.5–0.9 μm) stubby protrusions, the tips of which contained electron-dense, disk-shaped plaques, similar to the sarcocyst wall type 29b. In preliminary transmission attempts, a human volunteer did not excrete sporocysts in feces after ingesting 579 sarcocysts S. heydorni isolated from cattle. Phylogenetic analysis using the 2 molecular markers (18S rRNA gene and mitochondrial cox1 gene) indicated S. heydorni shared the closest affinity with species of Sarcocystis, which employ ruminants as intermediate hosts and canids as definitive hosts.
Haemogregarines are a group of apicomplexan parasites composed of 3 families that infect a wide range of hosts. Many species within these families have been subjected to reclassifications and reassignments, especially because the use of molecular tools to estimate their phylogenetic relationships became more widespread. The 18S rRNA gene has been the only widely used gene for studying the diversity of haemogregarines and recent phylogenetic analyses of this gene have indicated incongruences with the current taxonomy, such that a new genus Bartazoon has recently been proposed. To investigate the current taxonomic situation further, we conducted an overview of all published 18S rRNA sequence data for haemogregarines. We highlight that our understanding of the real diversity and phylogenetic relationships of haemogregarines is still limited, which undermines the proposed systematic revision. Notably all the molecular evidence comes from a single gene, and many studies have shown that single-gene trees often do not reflect species trees. Combined with doubts over the relationships of Hemolivia, the recent identification of a new lineage that could also warrant creation of a new genus, and issues with the type species for Hepatozoon, we suggest that any taxonomic changes now would be premature. In our opinion, type species need to be assessed, sampling across hosts improved, and multiple genes employed prior to taxonomic alterations. Otherwise taxonomic instability will be likely.
Invertebrate-derived ingested DNA (iDNA) is quickly proving to be a valuable, non-invasive tool for monitoring vertebrate species of conservation concern. Using the DNA barcoding locus, we successfully identified both the blood-feeding leech Haementeria acuecueyetzin and its blood meal—the latter is shown to be derived from the Caribbean manatee, Trichechus manatus. DNA amplification was successful despite the fact that the specimen was fixed in Mezcal (a beverage distilled from agave). We report the first confirmed case of a leech feeding on a manatee, the first record of H. acuecueyetzin for the State of Chiapas and, to our knowledge, the first case of successful DNA amplification of a biological sample fixed in Mezcal other than the caterpillar “worms” more commonly found in that beverage.
This study presents the structure of the capsule around the acanthocephalan Sphaerirostris picae (Rudolphi, 1819) Golvan, 1956, in its natural paratenic host, Lacerta agilis Linnaeus, 1758. The capsule was composed of 2 layers: a thin, dense inner layer and a loose, thick outer layer. The inner layer was formed by macrophages and multinucleated cells. The outer layer consisted mainly of flattened fibroblasts, which included a small number of macrophages, granulocytes, plasma cells, and pigment cells; the extensive intercellular spaces between these cells were filled with collagen fibers. The acanthocephalans are thought to have particular defense mechanisms that diminish phagocytic activity of immune system cells in the host.
We tested whether the probability of detecting avian haemosporidia (Plasmodium and Haemoproteus) using molecular techniques differs among blood, liver, heart, and pectoral muscle tissues. We used a paired design, sampling the 4 tissue types in 55 individuals of a wild South American suboscine antbird, the white-shouldered fire-eye (Pyriglena leucoptera). We also identified parasites to cytochrome b lineage. Detection probability was significantly lower in blood compared to the other 3 tissue types combined. Eight of 22 infections were not detected in blood samples; 4–7 infections were not detected in the other individual tissues. The same parasite lineage was recovered from different tissues.