Mb. Labruna et al., Risk factors to tick infestations and their occurrence on horses in the state of Sao Paulo, Brazil, VET PARASIT, 97(1), 2001, pp. 1-14
From December 1998 to March 1999, 40 stud farms were studied in the state o
f Sao Paulo, Brazil, During visits to farms, horses reared under grazing co
nditions were examined for the presence of ticks. On each farm visit, horse
pastures were closely inspected and a questionnaire was given to the farm
supervisor with the purpose of gaining information about ecological and man
agement variables (independent variables) that could be associated with the
presence and infestation levels of ticks on the farm (dependent variables)
. Three tick species were found during the study. Anocentor nitens, Amblyom
ma cajennense and Boophilus microplus were present on horses from 38 (95%),
20 (50%) and four (10%) farms, respectively. All farms that had A. cajenne
nse or B. microplus infestations also had A, nitens infestations, Only one
of the four farms with B, microplus infestations on the horses also had A.
cajennense infestations. Two farms had all horses free of ticks. There was
a strong association between the presence of infestation by B. microplus on
horses and the simultaneous use of a grazing area by cattle and horses (P
= 0.000). There was no statistical association between any of the independe
nt variables and the presence or infestation level of A. nitens on the hors
es (P > 0.20), The presence of A. cajennense was statistically associated w
ith the presence of at least one mixed overgrowth pasture in the farm (P =
0.001), A mixed overgrowth pasture means the presence of undesired plants s
uch as bushes and shrubs in the pasture, The presence of high levels of A.
cajennense on horses was also associated with the presence of at least one
mixed overgrowth pasture in the farm (P = 0.026), The regular use of acaric
ides was statistically associated with the presence of ticks on the horses
(P < 0.05), making this procedure a result of the inefficacy of controlling
ticks on the farms. The occurrence of human infestation by ticks was stati
stically associated with the presence of A. cajennense on the horses ( P =
0.000). The presence of at least one mixed overgrowth pasture on the farm w
as associated (P = 0.000) to either higher horse densities and to farms tha
t did not mow all the pastures once a year, indicating that mowing all the
pastures at least once a year can be considered a protective factor against
the presence of mixed overgrowth pastures on the farm, and consequently, a
gainst the presence of A. cajennense on the horses. (C) 2001 Elsevier Scien
ce B.V. All rights reserved.