Controlling tick-borne diseases through domestic animal management: a theoretical approach

Abstract

Vector-borne diseases are of global importance to human and animal health. Empirical trials of effective methods to control vectors and their pathogens can be difficult for practical, financial and ethical reasons. Here, therefore, we use a mathematical model to predict the effectiveness of a vector-borne disease control method. As a case study we use the tick-louping ill virus system, where sheep are treated with acaricide in an attempt to control ticks and disease in red grouse , an economically important game bird. We ran the model under different scenarios of sheep flock sizes, alternative host (deer) densities, acaricide efficacies and tick burdens. The model predicted that, with very low deer densities, using sheep as tick mops can reduce the tick population and virus prevalence. However, treatment is ineffective above a certain threshold deer density, dependent on the comparative tick burden on sheep and deer. The model also predicted that high efficacy levels of acaricide must be maintained for effective tick control. This study suggests that benignly managing one host species to protect another host species from a vector and pathogen can be effective under certain conditions. It also highlights the importance of understanding the ecological complexity of a system, in order to target control methods only under certain circumstances for maximum effectiveness.

The effects of acaricide treatment of sheep on red grouseLagopus lagopus scoticatick burdens and productivity in a multi‐host system

“…These results are similar to those found in northern England, where increasing the number of sheep treatments from two to four per annum reduced the tick burdens on grouse chicks by 90% (Newborn & Baines, ). Models that manipulated acaricide efficacy also highlighted that once efficacy reaches 70% (rather than 90% or 100%), the number of ticks may increase and grouse numbers decline (Porter et al ., ). In addition, reductions in the efficacy of these compounds can occur in sheep under extensive management systems as a result of the diluting effect of rainfall.…”

“…This is likely to be because the sites with lower deer densities were also those with higher red grouse densities (Table ). Modelling predicted that only at deer densities of fewer than six deer/km 2 , and low tick burdens on sheep treated with an effective acaricide, would tick levels would decline (Porter et al ., ). However, the present study did not detect a difference in the relationship between acaricide treatment interval and grouse tick burden according to whether deer density reflected fewer than six deer/km 2 or six or more deer/km 2 .…”

Investigating the loss of recruitment potential in red grouse (Lagopus lagopus scoticus): the relative importance of hen mortality, food supply, tick infestation and louping-ill

“…Similarly, the effectiveness of sheep tick-mop flocks is only likely to be effective when alternative hosts such as red deer are reduced to very low levels (Porter et al 2011). While vaccinating sheep against LIV can be effective in reducing LIV in grouse (GWCT 2011); this has also only been successful where alternative tick hosts are at low densities 2 .…”

Benefit to end users: appraisal of extending technology at farm fields from regions of Himachal Pradesh, India

“…Farmers did not perceive benefit of technology and unable to seek site specific requirements (Latynskiy & Berger, 2016). Ecological complexity of tick in farmers field need to be visualized while strategizing treatment (Porter et al, 2010). The movement of technology from lab to field has been a challenge and innovative ways have to be identified.…”