Characterization of Cattle Anal Odour Blend Responsible for Repellency against Rhipicephalus Appendiculatus, the Vector of East Coast Fever
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Date
2014-03-06
Authors
Kariuki, Margaret Wangechi
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Abstract
East Coast fever (ECF) is one of the most devastating livestock diseases in east,
central and southern Africa, and remains the major health hindrance to the
development and improvement of the livestock industry. Although synthetic chemical
acaricides have made a tremendous impact over the years in the control and
management of the vectors on livestock, ticks have developed resistance to most of
them In addition, these chemicals are toxic to non-target organisms. Previous on-host
behavior studies of adult R. appendiculatus showed preference to feed mainly inside
and around the ear of their hosts. Combination of a repellent blend from the anal
region and attractive blend at the ear has been sho-wn to play natural "push" and
"pull" roles, respectively, to guide these ticks to the cattle ears. The present study
aimed at characterizing and evaluating the constituents and blend in cattle anal odour
responsible for repelling adults of brown ear tick. The anal odours, and for
comparison, odours emanating from fresh dung were analyzed by gas
chromatography-linked mass spectrometry (GC-MS). The individual constituents
were identified by comparing their mass spectra with those in the National Institute of
Standards and Technology (NIST) libraries. The major constituents of the anal odour
were diisobutylphthalate (41.27%), o-xylene (9.2%), 4-hydroxy-4-methyl-2-
pentanone (4.6%), 4-methyl-2-methoxyphenol (4.3%), ethyl benzene (2.7%), 2,6,6-
trimethyl-[IS(la,~,5a)]bicycloheptanes (0.6%), 5-ethoxydihydro-2(3H)-furanone
(0.5%), 3-methylene-2-pentanone, (0.5%), 5-methyl-2-phenyl-1H-indole (0.4%), and
3-pentanone (0.2%). Three compounds namely 4-hydroxy-4-methyl-2-pentanone, N-
(3-methyl-l-oxobutyl)-alanine methyl ester and 2,4-dimethyl-benzo[h ]quinoline)
were common in both anal and dung odours. The repellency of odours, selected
constituents, blends and DEET was evaluated using two choice climbing assay. The
anal and fresh dung odour had comparable repellence (RD50 2.7 and 2.9,
respectively). Of the individual compounds tested, 4-methyl-2-methoxyphenol was
found to be most repellent (RD75 =0.56) while 3-pentanone was least active (RD75 =
622.7). The two blends evaluated were more repellent than the anal and dung odours.
One of the blends (made up of 4-methyl-2-methoxyphenol, 3-pentanone, 3-methyl-2-
pentanone, and 4-hydroxy-4-methyl-2-pentanone) tested gave RD75 of 0.032. The
other blend (without 3-pentanone) was more repellent (RD75= 0.019; P ::S 0.05, SNK).
In addition, of the analogues tested, 2,4-dimethylphenol was most repellent (RD75=
0.0089) while 3,4-methylenedioxytoluene was inactive. The study lays down the
groundwork for characterizing compounds and/or blends with potent repellence
against the Brown Ear Tick on cattle.
Description
Department of Physics, 2013. SF 810 .T5K3