Reducing sampling error in faecal egg counts from black rhinoceros (Diceros bicornis)

A Review of Non-Invasive Sampling in Wildlife Disease and Health Research: What's New?

In the last decades, wildlife diseases and the health status of animal populations have gained increasing attention from the scientific community as part of a One Health framework. Furthermore, the need for non-invasive sampling methods with a minimal impact on wildlife has become paramount in complying with modern ethical standards and regulations, and to collect high-quality and unbiased data. We analysed the publication trends on non-invasive sampling in wildlife health and disease research and offer a comprehensive review on the different samples that can be collected non-invasively. We retrieved 272 articles spanning from 1998 to 2021, with a rapid increase in number from 2010. Thirty-nine percent of the papers were focussed on diseases, 58% on other health-related topics, and 3% on both. Stress and other physiological parameters were the most addressed research topics, followed by viruses, helminths, and bacterial infections. Terrestrial mammals accounted for 75% of all publications, and faeces were the most widely used sample. Our review of the sampling materials and collection methods highlights that, although the use of some types of samples for specific applications is now consolidated, others are perhaps still underutilised and new technologies may offer future opportunities for an even wider use of non-invasively collected samples.

Quantifying the load of Echinococcus granulosus eggs in experimental dog infection using probe-based copro-qPCR analysis

Designing and implementing Cystic Echinococcosis control programs require quantitative information about the worm load and the intensity of infection in dog populations in endemic areas. So far no "probe-based" molecular quantification tool has been available for E. granulosus. This study was conducted in order to develop and evaluate a qPCR technique for measuring worm load of E. granulosus in the final host. A species-specific TaqMan probe was designed based on the available sequences in GenBank. The study was conducted in two stages. First, stool samples from an experimentally infected dog were collected in days 7, 14, 21, 28, 35 and 49, and were analyzed by real-time qPCR assay. In the second stage, 600 mg negative stool specimens were manually spiked with 1, 5, 10, 20 and 40 eggs and the specimens were analyzed using real-time qPCR. According to the standard curve analysis, 93% efficiency and coefficients of correlation (Rsq) > 0.991 were documented. Quantitative PCR assays showed an increasing signal of infection during the 7-week course of infection. As revealed by the qPCR results from week 5 onward, signals indicative of egg excretion began and reached maximum on week 7. No qPCR signal from the samples containing 1, 10 and 20 eggs was recorded, however the samples containing 5 and 40 eggs produced signals proportional to the primary DNA. The study presents a molecular tool to quantify the burden of E. granulosus infection in dogs. This tool could be applied for measuring the burden of infection in the definitive hosts in surveillance and control programs.

A SURVEY OF GASTROINTESTINAL PARASITES OF WILD AND ORPHAN GREATER ONE-HORNED RHINO ( RHINOCEROS UNICORNIS) IN KAZIRANGA NATIONAL PARK, ASSAM, INDIA

Wild greater one-horned rhinos ( Rhinoceros unicornis), orphaned juveniles in human care, and orphaned calves from Kaziranga National Park, Assam, India were surveyed coprologically for gastrointestinal parasites. Parasite infections were present in 100% of wild rhino samples, 96% of orphaned juvenile samples, and 27% of orphaned calf samples. In wild rhino, observed parasite ova were primarily of trematodes Paramphistomum sp. (100%), followed by those of strongyle nematodes (94%) and the cestode Anoplocephala sp. (56%). Orphaned juvenile and calf samples were positive only for strongyles. Total fecal parasite egg counts were recorded in wild rhino (mean 64 eggs per gram [epg], range 0-270), orphan juveniles (mean 43 epg, range 0-145), and orphan calves (mean 2 epg, range 0-10). Results suggest that parasite infection in rhinos in this setting is common, though more extensive sampling would provide further information on epidemiology and potential impacts on individual health and population viability.

Evaluating the Effects of Ivermectin Treatment on Communities of Gastrointestinal Parasites in Translocated Woylies (Bettongia penicillata)

Wildlife species are often treated with anti-parasitic drugs prior to translocation, despite the effects of this treatment being relatively unknown. Disruption of normal host-parasite relationships is inevitable during translocation, and targeted anti-parasitic drug treatment may exacerbate this phenomenon with inadvertent impacts on both target and non-target parasite species. Here, we investigate the effects of ivermectin treatment on communities of gastrointestinal parasites in translocated woylies (Bettongia penicillata). Faecal samples were collected at three time points (at the time of translocation, and 1 and 3 months post-translocation) and examined for nematode eggs and coccidian oocysts. Parasite prevalence and (for nematodes) abundance were estimated in both treated and untreated hosts. In our study, a single subcutaneous injection of ivermectin significantly reduced Strongyloides-like egg counts 1 month post-translocation. Strongyle egg counts and coccidia prevalence were not reduced by ivermectin treatment, but were strongly influenced by site. Likewise, month of sampling rather than ivermectin treatment positively influenced body condition in woylies post-translocation. Our results demonstrate the efficacy of ivermectin in temporarily reducing Strongyloides-like nematode abundance in woylies. We also highlight the possibility that translocation-induced changes to host density may influence coinfecting parasite abundance and host body condition post-translocation.

A standardised faecal collection protocol for intestinal helminth egg counts in Asian elephants, Elephas maximus

The quantitative assessment of parasite infection is necessary to measure, manage and reduce infection risk in both wild and captive animal populations. Traditional faecal flotation methods which aim to quantify parasite burden, such as the McMaster egg counting technique, are widely used in veterinary medicine, agricultural management and wildlife parasitology. Although many modifications to the McMaster method exist, few account for systematic variation in parasite egg output which may lead to inaccurate estimations of infection intensity through faecal egg counts (FEC). To adapt the McMaster method for use in sampling Asian elephants (Elephas maximus), we tested a number of possible sources of error regarding faecal sampling, focussing on helminth eggs and using a population of over 120 semi-captive elephants distributed across northern Myanmar. These included time of day of defecation, effects of storage in 10% formalin and 10% formol saline and variation in egg distribution between and within faecal boluses. We found no significant difference in the distribution of helminth eggs within faecal matter or for different defecation times, however, storage in formol saline and formalin significantly decreased egg recovery. This is the first study to analyse several collection and storage aspects of a widely-used traditional parasitology method for helminth parasites of E. maximus using known host individuals. We suggest that for the modified McMaster technique, a minimum of one fresh sample per elephant collected from any freshly produced bolus in the total faecal matter and at any point within a 7.5 h time period (7.30am-2.55 pm) will consistently represent parasite load. This study defines a protocol which may be used to test pre-analytic factors and effectively determine infection load in species which produce large quantities of vegetative faeces, such as non-ruminant megaherbivores.

Host density drives macroparasite abundance across populations of a critically endangered megaherbivore

What determines the abundance of parasites is a central question within epidemiology. Epidemiological models predict that density-dependent transmission has a principal influence on parasite abundance. However, this mechanism is seldom tested in macroparasites, perhaps because multiple, comparable populations of the same host-parasite relationship are rare. We test the influence of a range of factors on parasite abundance across 18 populations of black rhinoceros (Diceros bicornis) in South Africa. Here we show that host density strongly predicts parasite abundance at the population level for both directly and indirectly transmitted parasites. All other models were not supported. The surprising influence of a single key factor, host density, within a complex ecological system demonstrates the validity of simple epidemiological models. Establishing this previously assumed relationship between host density and parasite abundance has major implications for disease control and parasite ecology. For instance, it is central to the idea of population density thresholds for parasitism, below which a parasite would become extinct. Density-dependent transmission is also essential for calculations of the basic reproductive number, and the hypothesis that parasites may regulate host population size.