Jan Van Wyk - Academia.edu (original) (raw)
Papers by Jan Van Wyk
Journal of animal science/Journal of animal science ... and ASAS reference compendium, Mar 1, 2024
Journal of Animal Science, Nov 5, 2023
Veterinary Parasitology, 1997
We became increasingly concerned about indications of possible substandard efficacy of some gener... more We became increasingly concerned about indications of possible substandard efficacy of some generic anthelmintics, particularly after P.C. van Schalkwyk (personal communication, 1990) had found some batches of imported generic products obtained from international brokers to be poorly active, despite apparently normal physical characteristics. Therefore, considering the serious consequences this would have for sheep farming, it was decided to test the efficacy of some of the generic rafoxanide products available on the South African market. One of the three commercial formulations (of highly reputable companies) tested against a known susceptible strain of Haemonchus contortus in sheep was markedly substandard, with an arithmetic mean efficacy of 66.2% (Class B, Reinecke, 1973), compared to Class A efficacy of the other two, which also differed significantly from one another (Mann-Whitney; P = 0.01). Larger differences were found between the three products against a natural infection with a partially resistant strain of H. contortus than against the susceptible strain, with corresponding arithmetic mean efficacies of 28.7% (Class X, or ineffective), 71.3% (Class B) and 87.7% (also Class B). It is concluded that the most likely reason for the observed differences is that international brokers do not disclose the sources of supply of different batches of active ingredient (with the result that the companies buying anthelmintics from them have no way of telling when a source of supply is changed); that the efficacy of such batches differs; and that efficacy testing of individual batches in some cases is inadequate. It is suggested that registering authorities should consider simplified efficacy testing of each new batch of active ingredient before it may be marketed.
Veterinary Parasitology, 2006
Seriously escalating global anthelmintic resistance in gastrointestinal nematodes of small rumina... more Seriously escalating global anthelmintic resistance in gastrointestinal nematodes of small ruminants has spawned a variety of alternatives to anthelmintics for worm management, based on the need for sustainable Integrated Parasite Management (sIPM). Pivotal to the sIPM approach is the concept of refugia, the proportion of a given parasite population that escapes exposure to control measures. By balancing drug applications with the maintenance of refugia, the accumulation of anthelmintic resistance alleles in worm populations can be considerably delayed, while still providing good levels of control. The over-dispersed nature of parasitic infections provides an opportunity to achieve this balance, by targeting treatments to the members of a flock or herd that are least tolerant to nematode infection. However, implementation of this strategy has only recently become feasible, with the development of the FAMACHA # system for clinical evaluation of anaemia due to haemonchosis. Subsequently, the use of milk yields has proven an effective indicator in dairy goats infected predominantly with nematodes other than Haemonchus contortus. In addition, short-term weight changes and perhaps also body condition scoring may provide indices of parasitism, permitting the rapid identification of animals likely to benefit from treatment. However, sIPM and refugia-based approaches are more complex than whole-flock treatments in conventional programs, and adoption by farmers is most likely where the theoretical basis is understood. As close communication with informed advisors is generally limited, there is a danger that sIPM will remain a theoretical concept without alternative modes of communication. The development of computer-based decision support programs, which use epidemiological, seasonal and clinical information to provide recommendations for specific situations, should be accorded high priority in the future development of worm management systems.
Small Ruminant Research, 2005
... life ( [Neitz, 1968] and [27] ). These ticks occur in frost-free, relatively dry bushveld tha... more ... life ( [Neitz, 1968] and [27] ). These ticks occur in frost-free, relatively dry bushveld that is particularly suited to goats, and heartwater may be a major factor affecting profitable goat farming. Sheep and goats are more susceptible ...
Journal of animal science/Journal of animal science ... and ASAS reference compendium, Mar 1, 2024
An inability to control worms in the event of severe anthelmintic resistance can have extremely s... more An inability to control worms in the event of severe anthelmintic resistance can have extremely serious consequences - making farming with small ruminants unprofitable. Farmers spend more money on combating these diseases and experience more economic losses than for any other grouping of diseases.
Parasites & Vectors
Background Veterinary diagnostics aid intervention strategies, track zoonoses, and direct selecti... more Background Veterinary diagnostics aid intervention strategies, track zoonoses, and direct selective breeding programs in livestock. In ruminants, gastrointestinal nematode (GIN) parasites are a major cause of production losses, but morphologically similar species limit our understanding of how specific GIN co-infections impact health in resource-limited settings. To estimate the presence and relative abundance of GINs and other helminths at the species level, we sought to develop a low-cost and low-resource molecular toolkit applied to goats from rural Malawi smallholdings. Methods Goats were subjected to health scoring and faecal sampling on smallholdings in Lilongwe district, Malawi. Infection intensities were estimated by faecal nematode egg counts with a faecal subsample desiccated for DNA analysis. Two DNA extraction methods were tested (low-resource magbead kit vs high-resource spin-column kit), with resulting DNA screened by endpoint polymerase chain reaction (PCR), semi-quan...
Code for these data available at https://github.com/jogwalker/parasite\_transmission\_Q
Code for these data available at https://github.com/jogwalker/parasite\_transmission\_Q
Code for these data available at https://github.com/jogwalker/parasite\_transmission\_Q
Data used for logistic regression evaluating associations with high FAMACHA score (indicating ane... more Data used for logistic regression evaluating associations with high FAMACHA score (indicating anemia) before and after the rainy season. Reported in paper section "Spatial and seasonal variability in parasite burden in goats"
1.Transmission of parasites between host species affects host population dynamics, interspecific ... more 1.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. 2.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. 3.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. 4.Simulated transmission potential matches observed patterns of clinical disease in the study area. Increased wildlife contact is correlated with a decrease in disease, suggesting that noncompetent wild hosts may attenuate transmission by removing infective parasite larvae from livestock pasture. 5.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. 6.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
Agriculture
Lack of attention to rural healthcare for livestock in the southeastern United States has led to ... more Lack of attention to rural healthcare for livestock in the southeastern United States has led to a focus on small ruminant farming, mainly using sericea lespedeza [SL; Lespedeza cuneata (Dum-Cours) G. Don], a drought-resistant forage species with nutraceutical benefits. Climate change has increased land availability for SL cultivation, further expanding the potential of this bioactive (anti-parasitic) legume. This study aims to create a geospatial engineering and technology-assisted model for identifying suitable SL production areas for supporting profitable small ruminant farming. The cultivation of SL depends on specific weather conditions and soil properties, with minimum requirements for temperature and rainfall, non-clay soil with reduced bulk density, and open land cover. The main objective was to develop an automated geospatial model using ArcGIS Pro ModelBuilder to assess SL production suitability. This model also aimed to identify appropriate locations for small ruminant pr...
2023 IST-Africa Conference (IST-Africa)
Smallholder goat production plays a major role in rural livelihoods and food security in Malawi. ... more Smallholder goat production plays a major role in rural livelihoods and food security in Malawi. While goat production is closely linked to small scale local markets for slaughter and butchering the perspectives of butchers and their potential as a source of information on animal health is largely untapped. Understanding butchers’ perceptions of factors impacting goat smallholdings is important to identify hardships for both butchers and smallholders. Butchers can provide insights into goat health issues that go unseen before slaughter, including the presence of indigestible foreign bodies (IFBs), which can impact negatively on goat health but are difficult to diagnose before death. The current study includes a survey of 50 butchers in central Malawi to investigate visible animal health issues before and after slaughter, attitudes to procurement, income, and impacts of covid-19 on business. Results revealed butchers find IFBs to be a problem, with 100% of butchers witnessing plastic...
Agriculture, Ecosystems & Environment, 2018
Microclimate has a greater influence than macroclimate on the availability of infective Haemonchu... more Microclimate has a greater influence than macroclimate on the availability of infective Haemonchus contortus larvae on herbage in a warmed temperate environment
Preventive veterinary medicine, 2016
Infection with the abomasal nematode Haemonchus contortus is responsible for considerable product... more 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 ...
Journal of animal science/Journal of animal science ... and ASAS reference compendium, Mar 1, 2024
Journal of Animal Science, Nov 5, 2023
Veterinary Parasitology, 1997
We became increasingly concerned about indications of possible substandard efficacy of some gener... more We became increasingly concerned about indications of possible substandard efficacy of some generic anthelmintics, particularly after P.C. van Schalkwyk (personal communication, 1990) had found some batches of imported generic products obtained from international brokers to be poorly active, despite apparently normal physical characteristics. Therefore, considering the serious consequences this would have for sheep farming, it was decided to test the efficacy of some of the generic rafoxanide products available on the South African market. One of the three commercial formulations (of highly reputable companies) tested against a known susceptible strain of Haemonchus contortus in sheep was markedly substandard, with an arithmetic mean efficacy of 66.2% (Class B, Reinecke, 1973), compared to Class A efficacy of the other two, which also differed significantly from one another (Mann-Whitney; P = 0.01). Larger differences were found between the three products against a natural infection with a partially resistant strain of H. contortus than against the susceptible strain, with corresponding arithmetic mean efficacies of 28.7% (Class X, or ineffective), 71.3% (Class B) and 87.7% (also Class B). It is concluded that the most likely reason for the observed differences is that international brokers do not disclose the sources of supply of different batches of active ingredient (with the result that the companies buying anthelmintics from them have no way of telling when a source of supply is changed); that the efficacy of such batches differs; and that efficacy testing of individual batches in some cases is inadequate. It is suggested that registering authorities should consider simplified efficacy testing of each new batch of active ingredient before it may be marketed.
Veterinary Parasitology, 2006
Seriously escalating global anthelmintic resistance in gastrointestinal nematodes of small rumina... more Seriously escalating global anthelmintic resistance in gastrointestinal nematodes of small ruminants has spawned a variety of alternatives to anthelmintics for worm management, based on the need for sustainable Integrated Parasite Management (sIPM). Pivotal to the sIPM approach is the concept of refugia, the proportion of a given parasite population that escapes exposure to control measures. By balancing drug applications with the maintenance of refugia, the accumulation of anthelmintic resistance alleles in worm populations can be considerably delayed, while still providing good levels of control. The over-dispersed nature of parasitic infections provides an opportunity to achieve this balance, by targeting treatments to the members of a flock or herd that are least tolerant to nematode infection. However, implementation of this strategy has only recently become feasible, with the development of the FAMACHA # system for clinical evaluation of anaemia due to haemonchosis. Subsequently, the use of milk yields has proven an effective indicator in dairy goats infected predominantly with nematodes other than Haemonchus contortus. In addition, short-term weight changes and perhaps also body condition scoring may provide indices of parasitism, permitting the rapid identification of animals likely to benefit from treatment. However, sIPM and refugia-based approaches are more complex than whole-flock treatments in conventional programs, and adoption by farmers is most likely where the theoretical basis is understood. As close communication with informed advisors is generally limited, there is a danger that sIPM will remain a theoretical concept without alternative modes of communication. The development of computer-based decision support programs, which use epidemiological, seasonal and clinical information to provide recommendations for specific situations, should be accorded high priority in the future development of worm management systems.
Small Ruminant Research, 2005
... life ( [Neitz, 1968] and [27] ). These ticks occur in frost-free, relatively dry bushveld tha... more ... life ( [Neitz, 1968] and [27] ). These ticks occur in frost-free, relatively dry bushveld that is particularly suited to goats, and heartwater may be a major factor affecting profitable goat farming. Sheep and goats are more susceptible ...
Journal of animal science/Journal of animal science ... and ASAS reference compendium, Mar 1, 2024
An inability to control worms in the event of severe anthelmintic resistance can have extremely s... more An inability to control worms in the event of severe anthelmintic resistance can have extremely serious consequences - making farming with small ruminants unprofitable. Farmers spend more money on combating these diseases and experience more economic losses than for any other grouping of diseases.
Parasites & Vectors
Background Veterinary diagnostics aid intervention strategies, track zoonoses, and direct selecti... more Background Veterinary diagnostics aid intervention strategies, track zoonoses, and direct selective breeding programs in livestock. In ruminants, gastrointestinal nematode (GIN) parasites are a major cause of production losses, but morphologically similar species limit our understanding of how specific GIN co-infections impact health in resource-limited settings. To estimate the presence and relative abundance of GINs and other helminths at the species level, we sought to develop a low-cost and low-resource molecular toolkit applied to goats from rural Malawi smallholdings. Methods Goats were subjected to health scoring and faecal sampling on smallholdings in Lilongwe district, Malawi. Infection intensities were estimated by faecal nematode egg counts with a faecal subsample desiccated for DNA analysis. Two DNA extraction methods were tested (low-resource magbead kit vs high-resource spin-column kit), with resulting DNA screened by endpoint polymerase chain reaction (PCR), semi-quan...
Code for these data available at https://github.com/jogwalker/parasite\_transmission\_Q
Code for these data available at https://github.com/jogwalker/parasite\_transmission\_Q
Code for these data available at https://github.com/jogwalker/parasite\_transmission\_Q
Data used for logistic regression evaluating associations with high FAMACHA score (indicating ane... more Data used for logistic regression evaluating associations with high FAMACHA score (indicating anemia) before and after the rainy season. Reported in paper section "Spatial and seasonal variability in parasite burden in goats"
1.Transmission of parasites between host species affects host population dynamics, interspecific ... more 1.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. 2.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. 3.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. 4.Simulated transmission potential matches observed patterns of clinical disease in the study area. Increased wildlife contact is correlated with a decrease in disease, suggesting that noncompetent wild hosts may attenuate transmission by removing infective parasite larvae from livestock pasture. 5.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. 6.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
Agriculture
Lack of attention to rural healthcare for livestock in the southeastern United States has led to ... more Lack of attention to rural healthcare for livestock in the southeastern United States has led to a focus on small ruminant farming, mainly using sericea lespedeza [SL; Lespedeza cuneata (Dum-Cours) G. Don], a drought-resistant forage species with nutraceutical benefits. Climate change has increased land availability for SL cultivation, further expanding the potential of this bioactive (anti-parasitic) legume. This study aims to create a geospatial engineering and technology-assisted model for identifying suitable SL production areas for supporting profitable small ruminant farming. The cultivation of SL depends on specific weather conditions and soil properties, with minimum requirements for temperature and rainfall, non-clay soil with reduced bulk density, and open land cover. The main objective was to develop an automated geospatial model using ArcGIS Pro ModelBuilder to assess SL production suitability. This model also aimed to identify appropriate locations for small ruminant pr...
2023 IST-Africa Conference (IST-Africa)
Smallholder goat production plays a major role in rural livelihoods and food security in Malawi. ... more Smallholder goat production plays a major role in rural livelihoods and food security in Malawi. While goat production is closely linked to small scale local markets for slaughter and butchering the perspectives of butchers and their potential as a source of information on animal health is largely untapped. Understanding butchers’ perceptions of factors impacting goat smallholdings is important to identify hardships for both butchers and smallholders. Butchers can provide insights into goat health issues that go unseen before slaughter, including the presence of indigestible foreign bodies (IFBs), which can impact negatively on goat health but are difficult to diagnose before death. The current study includes a survey of 50 butchers in central Malawi to investigate visible animal health issues before and after slaughter, attitudes to procurement, income, and impacts of covid-19 on business. Results revealed butchers find IFBs to be a problem, with 100% of butchers witnessing plastic...
Agriculture, Ecosystems & Environment, 2018
Microclimate has a greater influence than macroclimate on the availability of infective Haemonchu... more Microclimate has a greater influence than macroclimate on the availability of infective Haemonchus contortus larvae on herbage in a warmed temperate environment
Preventive veterinary medicine, 2016
Infection with the abomasal nematode Haemonchus contortus is responsible for considerable product... more 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 ...