Treatment of cattle with ivermectin and its effect on dung degradation and larval abundance in a tropical savanna setting
Miriam Ruhinda,
Kang Xia,
Cassidy Rist,
Gerald Shija,
Issa N. Lyimo,
Felician Meza,
Carlyle Brewster,
Carlos Chaccour,
N. Regina Rabinovich,
Roger Schürch
Affiliations
Miriam Ruhinda
Department of Entomology, Virgina Polytechnic Institute & State University, Blacksburg, VA 24061, USA; Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Tanzania; Corresponding author at: Department of Entomology, Kansas State University, Manhattan, KS 66506, USA.
Kang Xia
School of Plant and Environmental Sciences, Virgina Polytechnic Institute & State University, Blacksburg, VA 24061, USA
Cassidy Rist
Department of Population Health Sciences, Virgina Polytechnic Institute & State University, Blacksburg, VA 24061, USA
Gerald Shija
School of Plant and Environmental Sciences, Virgina Polytechnic Institute & State University, Blacksburg, VA 24061, USA; Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Tanzania; Chemistry Department, College of Natural and Mathematical Sciences, The University of Dodoma, Dodoma, Tanzania
Issa N. Lyimo
Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Tanzania; School of Life Sciences and Bioengineering, Nelson Mandela African Institution of Science and Technology, Tengeru, Arusha, Tanzania
Felician Meza
Environmental Health and Ecological Sciences Department, Ifakara Health Institute, Tanzania
Carlyle Brewster
Plant and Environmental Sciences Department, Clemson University, SC 29634, USA
Carlos Chaccour
ISGlobal, Barcelona Institute for Global Health, Barcelona, Spain; Universidda de Navarra, Pamplona, Spain; Centro de Investigación Biomédica en Red de Enfermedades Infecciosas, Madrid, Spain
N. Regina Rabinovich
ISGlobal, Barcelona Institute for Global Health, Barcelona, Spain; TH Chan Harvard School of Public Health, Boston, USA
Roger Schürch
Department of Entomology, Virgina Polytechnic Institute & State University, Blacksburg, VA 24061, USA
When ingested as part of a blood meal, the antiparasitic drug ivermectin kills mosquitoes, making it a candidate for mass drug administration (MDA) in humans and livestock to reduce malaria transmission. When administered to livestock, most ivermectin is excreted unmetabolized in the dung within 5 days post administration. Presence of ivermectin, has been shown to adversely affect dung colonizers and dung degradation in temperate settings; however, those findings may not apply to, tropical environment, where ivermectin MDA against malaria would occur. Here we report results of a randomized field experiment conducted with dung from ivermectin-treated and control cattle to determine the effect of ivermectin on dung degradation in tropical Tanzania. For intact pats, we measured termite colonization, larval numbers and pat wet and dry weights. Pat organic matter was interpolated from a subsample of the pat (10 g wet weight). Additionally, we counted larvae growing in the treated and untreated pats in a semi-field setting. We found that termites colonized ivermectin pats more readily than controls. Despite this, wet weight decreased significantly slower in the ivermectin-treated pats in the first two weeks. As water was lost, sub-sample dry weight increased, and organic matter decreased similarly over time for the treatment and control. Interpolated for whole pats, total organic matter was higher, and larval counts were lower in the ivermectin-treated pats after the first month. Our results demonstrate an effect of ivermectin and its metabolites on dung degradation and fauna in a tropical savanna setting. Because slow dung degradation and low insect abundance negatively impact pastureland, these non-target, environmental effects must be further investigated within the context of real-world implementation of ivermectin MDA in cattle and weighed against the potential benefits for malaria control.
