Resistance to cypermethrin, deltamethrin and chlorpyriphos in populations of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) from small farms of the State of Sao Paulo, Brazil

A field survey of resistance was conducted based on the larval packet test technique with synthetic pyrethroids (cypermethrin and deltamethrin) and organophosphates (chlorpyriphos) in Rhipicephalus (Boophilus) microplus field populations from six different regions of the State of Sao Paulo (Brazil). 82.6% of the populations showed resistance to cypermethrin, 86.36% to deltamethrin and 65.25% to chlorpyriphos, with 50% presenting resistance to both SP and OP acaricide. According to the questionnaires completed by the producers, OP + SP mixtures followed by SP-only formulations were the products most commonly used for controlling the cattle tick in the surveyed areas. The present study showed high occurrence of resistance to SP and OP in the State of Sao Paulo, Brazil and revealed the type of strategy adopted by small dairy farms in this state. This information is fundamental in order to establish the monitoring of resistance on each farm individually, contributing to the rational use of acaricides for the control of R. (B.) microplus. (C) 2011 Elsevier B.V. All rights reserved.

Age-Dependent Acquisition of Protective Immunity to Malaria in Riverine Populations of the Amazon Basin of Brazil

Five community-based cross-sectional surveys of malaria morbidity and associated risk factors in remote riverine populations in northwestern Brazil showed average parasite rates of 4.2% (thick-smear microscopy) and 14.4% (polymerase chain reaction [PCR]) in the overall population, with a spleen rate of 13.9% among children 2-9 years of age. Plasmodium vivax was 2.8 times more prevalent than P. falciparum, with rare instances of P. malariae and mixed-species infections confirmed by PCR; 9.6% of asymptomatic subjects had parasitemias detected by PCR. Low-grade parasitemia detected by PCR only was a risk factor for anemia, after controlling for age and other covariates. Although clinical and subclinical infections occurred in all age groups, the risk of infection and disease decreased significantly with increasing age, after adjustment for several covariates in multilevel logistic regression models. These findings suggest that the continuous exposure to hypo- or mesoendemic malaria may induce significant anti-parasite and anti-disease immunity in native Amazonians.