Climate change is likely to increase the development rate of anthelmintic resistance in equine cyathostomins in New Zealand

Abstract

Climate change is likely to influence livestock production by increasing the prevalence of diseases, including parasites. The traditional practice of controlling nematodes in livestock by the application of anthelmintics is, however, increasingly compromised by the development of resistance to these drugs in parasite populations. This study used a previously developed simulation model of the entire equine cyathostomin lifecycle to investigate the effect a changing climate would have on the development of anthelmintic resistance. Climate data from six General Circulation Models based on four different Representative Concentration Pathways was available for three New Zealand locations. These projections were used to estimate the time resistance will take to develop in the middle (2040–49) and by the end (2090–99) of the century in relation to current (2006–15) conditions under two treatment scenarios of either two or six yearly whole-herd anthelmintic treatments. To facilitate comparison, a scenario without any treatments was included as a baseline. In addition, the size of the infective and parasitic stage nematode population during the third simulation year were estimated. The development of resistance varied between locations, time periods and anthelmintic treatment strategies. In general, the simulations indicated a more rapid development of resistance under future climates coinciding with an increase in the numbers of infective larvae on pasture and encysted parasitic stages. This was especially obvious when climate changes resulted in a longer period suitable for development of free-living parasite stages. A longer period suitable for larval development resulted in an increase in the average size of the parasite population with a larger contribution from eggs passed by resistant worms surviving the anthelmintic treatments. It is projected that climate change will decrease the ability to control livestock parasites by means of anthelmintic treatments and non-drug related strategies will become increasingly important for sustainable parasite control.

Economic impact of gastrointestinal nematodes in Morada Nova sheep in Brazil

“…However, in a scenario of highly resistant parasites (Raschia et al, 2021), refugia preservation, favored by the TST approach, has become essential for maintaining the efficacy of anthelmintics, which must be used carefully (George et al, 2021). As highlighted by Sauermann et al (2020), any parasite in a pasture is only in refugia if it successfully develops to the adult stage and produces viable offspring. Otherwise, it does not contribute to the population genetics and must be disregarded in terms of refugia.…”

“…The rise in global temperature is leading to increased occurrence and alterations in the distribution of many infectious diseases. Recent reports by the Intergovernmental Panel on Climate Change and the Food and Agriculture Organization of the United Nations identified an increase in livestock diseases, including parasite infections, as a result of changing climate, with a negative impact on food security (Sauermann et al, 2020).…”

Parasite dynamics in untreated horses through one calendar year

“…However, as mentioned previously, most of these previous studies were conducted in the UK, and since very few studies have been completed elsewhere, these patterns may differ substantially between regions and climates. Recent work with a cyathostomin computer model has suggested widely different transmission patterns between seasons and climates [ 42 , 43 ], and it is therefore plausible that strongylid egg shedding patterns may differ between climates in a similar fashion. However, it should be acknowledged that the studied population may not be completely representative of managed horses in central Kentucky or elsewhere.…”

The Use of Molecular Profiling to Track Equine Reinfection Rates of Cyathostomin Species Following Anthelmintic Administration

“…Cyathostomin transmission is known to be seasonally regulated [ 55 , 60 ] based on both larvae and adult worm preferences for temperature and moisture. The optimum temperature for the development of strongyle eggs and larvae ranges from 25–33 °C [ 1 , 3 , 55 ] with an upper limit of 38 °C [ 61 ] and the optimal fecal moisture level of the closely related ruminant trichostrongylids is 57–63% with larval development not occurring below 20% [ 62 , 63 ].…”