Jan A. van Wyk

The mitochondrial genomes of Ancylostoma caninum and Bunostomum phlebotomum - two hookworms of animal health and zoonotic importance.

BackgroundHookworms are blood-feeding nematodes that parasitize the small intestines of many mammals, including humans and cattle. These nematodes are of major socioeconomic importance and cause disease, mainly as a consequence of anaemia (particularly in children or young animals), resulting in impaired development and sometimes deaths. Studying genetic variability within and among hookworm populations is central to addressing epidemiological and ecological questions, thus assisting in the control of hookworm disease. Mitochondrial (mt) genes are known to provide useful population markers for hookworms, but mt genome sequence data are scant.ResultsThe present study characterizes the complete mt genomes of two species of hookworm, Ancylostoma caninum (from dogs) and Bunostomum phlebotomum (from cattle), each sequenced (by 454 technology or primer-walking), following long-PCR amplification from genomic DNA (~20–40 ng) isolated from individual adult worms. These mt genomes were 13717 bp and 13790 bp in size, respectively, and each contained 12 protein coding, 22 transfer RNA and 2 ribosomal RNA genes, typical for other secernentean nematodes. In addition, phylogenetic analysis (by Bayesian inference and maximum likelihood) of concatenated mt protein sequence data sets for 12 nematodes (including Ancylostoma caninum and Bunostomum phlebotomum), representing the Ascaridida, Spirurida and Strongylida, was conducted. The analysis yielded maximum statistical support for the formation of monophyletic clades for each recognized nematode order assessed, except for the Rhabditida.ConclusionThe mt genomes characterized herein represent a rich source of population genetic markers for epidemiological and ecological studies. The strong statistical support for the construction of phylogenetic clades and consistency between the two different tree-building methods employed indicate the value of using whole mt genome data sets for systematic studies of nematodes. The grouping of the Spirurida and Ascaridida to the exclusion of the Strongylida was not supported in the present analysis, a finding which conflicts with the current evolutionary hypothesis for the Nematoda based on nuclear ribosomal gene data.

Can we slow the development of anthelmintic resistance? An electronic debate

Abstract An electronic conference, Managing Worms Sustainably – We Need to Reconsider Present Recommendations, held 4 March – 12 April 2002, was hosted online at: http://www.worms.org.za/news.asp

Sensitivity and specificity of the FAMACHA © system in Suffolk sheep and crossbred Boer goats

Sheep and goats are the species of farm animal with the highest growth rate in Paraná State. The main problems facing Paraná State flocks are gastrointestinal parasites and anthelmintic resistance. One of the newest resources used to slow down the development of anthelmintic resistance is the FAMACHA(©) system, a selective method useful for controlling gastrointestinal verminosis in small ruminants. The purpose of the present research was to evaluate the sensitivity and specificity of the FAMACHA(©) system in sheep and goats and to compare the results for both species. The conjunctivae of 83 Suffolk ewes and 60 adult crossbred Boer does were evaluated by the same trained person using the FAMACHA(©) system. The packed cell value (PCV) served as the gold standard for clinical FAMACHA(©) evaluation. To calculate the sensitivity and specificity of the FAMACHA(©) system, different criteria were adopted in turn: animals classified as FAMACHA(©) (F(©)) 4 and 5, or 3, 4 and 5, were considered to be anemic (positive test), and animals classified as F(©)1, 2 and 3, or 1 and 2 were considered to be non-anemic (negative test). Three standard values of PCV, namely ≤19%, ≤18% or ≤15%, were used to confirm anemia. At all cut-off levels, the sensitivity increased if F(©)3 animals were included as being anemic. However, changes in levels of sensitivity were associated with reciprocal changes in specificity. The sensitivity was higher for sheep than for goats, excepting when the criteria included PCV≤18 and F(©)3, F(©)4 and F(©)5 were considered positive. In contrast, the specificity was always lower in sheep for any criteria adopted. Other than in goats, using the ≤15 cut-off level for sheep, it is possible to opt not to drench the animals that were shown to be F(©)3 because the sensitivity is still high, indicating that few animals that should have been drenched were overlooked. In goats, in contrast, the low sensitivity at all cut-off levels made it too risky to leave F(©)3 animals undrenched. Even though the number of correct treatments for goats was always higher than that for sheep, the opposite was true for the kappa index for all the criteria tested. Therefore, the FAMACHA(©) system is suitable for the identification of anemic animals of both species. It is necessary that all small ruminants classified as FAMACHA(©) level 3 are also treated to increase the sensitivity of the method.

Assessment of a hands-on method for FAMACHA© system training.

The FAMACHA(©) system is a method for selective anthelmintic treatment comprising early detection of haemonchosis in sheep and goats. In order to evaluate the hands-on training methodology and the learning level of the participants, we analyzed data from 30 training events involving 47 training classes conducted in the State of Paraná, Brazil, from July/2009 to May/2011, during which period a total of 1004 participants did 20,080 FAMACHA(©) classifications. In the practical training sessions, each participant individually evaluated 20 animals with known haematocrit values. Every participant per training event was given a unique number, whereupon each of the animals in a given event was FAMACHA(©) classified by all the trainees involved, in the same trainee number sequence. After each consecutive animal had been evaluated by every one of the participants, its haematocrit and corresponding FAMACHA(©) category were announced before the next animal was presented. The number of persons in training, which ranged from 5 to 39 per session, did not significantly affect the average error of the groups of participants involved (p>0.05). The average error in the classification of the first animal on a scale with a perfect score of zero was 2.5, significantly greater than the error of 0.56 of the twentieth one (p<0.05), indicating an inverse relationship between the error and the cumulative number of animals already evaluated by each trainee involved, with the reduction in mean error per animal in a given training event found by linear regression to be 0.0713. When the same animal was assessed twice in the same training event, the average error of the second evaluation (1.05) was significantly lower than the 1.70 of the first (p<0.05). While the total of 686 sheep used in the training events (73%) was considerably larger than the corresponding number of 254 goats (27%), the average statistical errors, respectively, 1.34 and 1.23, were not significantly different (p>0.05). Similarly, the average errors in FAMACHA(©) classification were not significantly influenced by the occupation or gender of the participants, nor whether there were animals in all five FAMACHA(©) categories or only in categories 1, 2, 3 and 4 per training event (p>0.05).

FAMACHA©: A potential tool for targeted selective treatment of chronic fasciolosis in sheep.

The liver fluke Fasciola hepatica causes considerable damage to the health, welfare and productivity of ruminants in temperate areas, and its control is challenged by anthelmintic resistance. Targeted selective treatment (TST) is an increasingly established strategy for preserving anthelmintic efficacy in grazing livestock, yet no practical indicators are available to target individuals for treatment against fluke infection. This paper evaluates the FAMACHA(©) system, a colour chart for the non-invasive detection of anaemia in small ruminants, for this purpose. FAMACHA(©) scores were collected from 288 sheep prior to slaughter during the winter period, when fluke infections were largely mature, and condemned livers were recovered and adult flukes extracted. Average FAMACHA(©) score was significantly higher (=paler conjunctivae) in animals whose livers were condemned (3.6, n=62) than in those whose livers were not condemned (2.1). The number of adult flukes recovered ranged from 2 to 485, and was positively correlated with FAMACHA(©) score (r(2)=0.54, p<0.001). Packed cell volume was correlated negatively with both FAMACHA(©) score (n=240, r=0.23, p<0.001) and fluke number (r=0.24, p<0.001). Nematode faecal egg count (FEC) did not correlate with FAMACHA(©) score, and selective treatment of individual sheep with FAMACHA(©) scores above 2 or 3 would have preserved between 27 and 100% of nematodes in refugia on the basis of FEC, depending on group and the threshold used for treatment. FAMACHA(©) holds promise as a tool for selective treatment of sheep against adult F. hepatica, in support of refugia-based control of fluke and nematode infections, and further field evaluation is warranted.

Mixed methods evaluation of targeted selective anthelmintic treatment by resource-poor smallholder goat farmers in Botswana

Graphical abstract

Prediction and attenuation of seasonal spillover of parasites between wild and domestic ungulates in an arid mixed‐use system

Abstract Transmission of parasites between host species affects host population dynamics, interspecific competition, and ecosystem structure and function. In areas where wild and domestic herbivores share grazing land, management of parasites in livestock may affect or be affected by sympatric wildlife due to cross‐species transmission. We develop a novel method for simulating transmission potential based on both biotic and abiotic factors in a semi‐arid system in Botswana. Optimal timing of antiparasitic treatment in livestock is then compared under a variety of alternative host scenarios, including seasonally migrating wild hosts. In this region, rainfall is the primary driver of seasonality of transmission, but wildlife migration leads to spatial differences in the effectiveness of treatment in domestic animals. Additionally, competent migratory wildlife hosts move parasites across the landscape. Simulated transmission potential matches observed patterns of clinical disease in livestock in the study area. Increased wildlife contact is correlated with a decrease in disease, suggesting that non‐competent wild hosts may attenuate transmission by removing infective parasite larvae from livestock pasture. Optimising the timing of treatment according to within‐year rainfall patterns was considerably more effective than treating at a standard time of year. By targeting treatment in this way, efficient control can be achieved, mitigating parasite spillover from wildlife where it does occur. Synthesis and applications. This model of parasite transmission potential enables evidence‐based management of parasite spillover between wild and domestic species in a spatio‐temporally dynamic system. It can be applied in other mixed‐use systems to mitigate parasite transmission under altered climate scenarios or changes in host ranges.

An elaborated SIR model for haemonchosis in sheep in South Africa under a targeted selective anthelmintic treatment regime

Infection with the abomasal nematode Haemonchus contortus is responsible for considerable production loss in small ruminants globally, and especially in warm, summer-rainfall regions. Previous attempts to predict infection levels have followed the traditional framework for macroparasite models, i.e. tracking parasite population sizes as a function of host and climatic factors. Targeted treatment strategies, in which patho-physiological indices are used to identify the individuals most affected by parasites, could provide a foundation for alternative, incidence-based epidemiological models. In this paper, an elaboration of the classic susceptible-infected-recovered (SIR) model framework for microparasites was adapted to haemonchosis and used to predict disease in Merino sheep on a commercial farm in South Africa. Incidence was monitored over a single grazing season using the FAMACHA scoring system for conjunctival mucosal coloration, which indicates high burdens of H. contortus, and used to fit the model by estimating transmission parameters. The model predicted force of infection (FOI) between sequential FAMACHA monitoring events in groups of dry, pregnant and lactating ewes, and related FOI to factors including climate (temperature, rainfall and rainfall entropy), using a random effects model with reproductive status group as the cluster variable. Temperature and rainfall in the seven days prior to monitoring significantly predicted the interval FOI (p≤0.002), while rainfall entropy did not (p=0.289). Differences across the three groups accounted for approximately 90% of the variability in the interval FOI over the period of investigation. Maintained FOI during targeted treatment of cases of haemonchosis suggests strong underlying transmission from sub-clinically infected animals, and/or limited impact on pre-existing pasture contamination by removal of clinical worm burdens later in the grazing season. The model has the potential to contribute to the sustainable management of H. contortus by predicting periods of heightened risk, and hence to focus and optimise limited resources for monitoring and treatment. SIR-type model frameworks are an alternative to classic abundance-based compartmental models of macroparasite epidemiology, and could be useful where incidence data are available. Significant challenges remain, however, in the ability to calibrate such models to field data at spatial and temporal scales that are useful for decision support at farm level.

Corrigendum to “Sensitivity and specificity of the FAMACHA© system in Suffolk sheep and crossbred Boer goats” [Vet. Parasitol. 190 (2012) 114–119]

The authors reported an error in Table 2; the titles of the true-negative and true-positive columns are switched, and a corrected versionof Table 2 follows below.