Partial characterization of the voltage-gated sodium channel gene and molecular detection of permethrin resistance in Rhipicephalus annulatus (Say, 1821)

The cattle tick, Rhipicephalus annulatus (Say) is a vector of bovine babesiosis and responsible for direct and indirect losses to cattle producing areas located in temperate and subtropical dry regions. Resistance against pyrethroids has been reported for this species in Asia and Africa, but never before in North America. An outbreak strain, Rio Lado, collected close to the border between Mexico and the United States, in Maverick County, Texas, showed low level of resistance to permethrin, a pyrethroid pesticide. We used genomic material from different strains of cattle ticks collected within the Permanent Quarantine Zone (Rio Lado, Vega and Klein Grass strains) to partially characterize the coding gene of the voltage-gated sodium channel (Na-channel), target-site of pyrethroid pesticides, and search for putative mutations associated with resistance using quantitative PCR high resolution melt (HRM) analysis. The two amplified fragments, corresponding to domains II and III of the Na-channel, were 100 % identical to its ortholog in Rhipicephalus microplus (Canestrini). No nucleotide polymorphisms in the Na-channel gene were observed in the pyrethroid-resistant Rio Lado strain, when compared to the susceptible strains Klein Grass and Vega. This study reports the first case of pyrethroid resistance in R. annulatus collected in the United States. Also, we provide new genomic data for this species of tick that allows for the development of a new method to screen for mutations associated with pyrethroid resistance.

The contribution of a bacterially isolated environment to the prevention of infection in seriously burned patients

A new system of patient protection from bacterial crossinfection called the Bacteria Controlled Nursing Unit (BCNU) is described, based on strict environmental control of a 6 x 10 foot area surrounding the patient's bed rather than the entire patient room or isolation ward, plus the ability to deliver all medical care without entering the protective environment and maintaining all monitoring, life support, and i.v. equipment outside the controlled environment. The clinical effectiveness of this system in the treatment of burn patients has been studied and compared with the effectiveness of single room isolation on a burn isolation ward and conventional isolation techniques on an open burn ward. The studies show that the BCNU is significantly more effective in preventing bacterial cross-contamination than conventional precautions (3.8% vs. 13.1%, P < 0.001; and 8% vs. 22.8%, P < 0.001) over a two and four week period. The studies also indicate that there was a significant increase in the probability of infection occurring following cross-contamination than occurring after auto-contamination (65% vs. 39%, P < 0.005), emphasizing the importance of preventing cross-contamination in reducing the overall infection rate in seriously burned patients. Clinical evaluation of the unit proved it to be compatible with intensive nursing and medical care without increasing the nurse to patient ratio. The unit provided sufficient control of bacterial cross-infection to allow reduction in mortality and improvement in the effectiveness of burn care through routine prompt excision of burn eschar and immediate wound closure to be carried out in severe and massively burned patients without a limiting threat of bacterial burn wound sepsis.