João Ricardo Martins

Reassessment of the potential economic impact of cattle parasites in Brazil

The profitability of livestock activities can be diminished significantly by the effects of parasites. Economic losses caused by cattle parasites in Brazil were estimated on an annual basis, considering the total number of animals at risk and the potential detrimental effects of parasitism on cattle productivity. Estimates in U.S. dollars (USD) were based on reported yield losses among untreated animals and reflected some of the effects of parasitic diseases. Relevant parasites that affect cattle productivity in Brazil, and their economic impact in USD billions include: gastrointestinal nematodes -

First report of fluazuron resistance in Rhipicephalus microplus: A field tick population resistant to six classes of acaricides

7.11; cattle tick (Rhipicephalus (Boophilus) microplus) -

Multiple resistance to acaricides in field populations of Rhipicephalus microplus from Rio Grande do Sul state, Southern Brazil

3.24; horn fly (Haematobia irritans) -

Spotted Fever Group Rickettsia in the Pampa Biome, Brazil, 2015–2016

2.56; cattle grub (Dermatobia hominis) -

Does Rhipicephalus microplus tick infestation increase the risk for myiasis caused by Cochliomyia hominivorax in cattle

0.38; New World screwworm fly (Cochliomyia hominivorax) -

Integrated control of an acaricide-resistant strain of the cattle tick Rhipicephalus microplus by applying Metarhizium anisopliae associated with cypermethrin and chlorpyriphos under field conditions.

0.34; and stable fly (Stomoxys calcitrans) -

Characterization of the pyrethroid resistance profile of Rhipicephalus (Boophilus)microplus populations from the states of Rio Grande do Sul and Mato Grosso do Sul, Brazil

0.34. The combined annual economic loss due to internal and external parasites of cattle in Brazil considered here was estimated to be at least USD 13.96 billion. These findings are discussed in the context of methodologies and research that are required in order to improve the accuracy of these economic impact assessments. This information needs to be taken into consideration when developing sustainable policies for mitigating the impact of parasitism on the profitability of Brazilian cattle producers.

Rickettsia parkeri in Amblyomma dubitatum ticks in a spotted fever focus from the Brazilian Pampa

The control of the cattle tick Rhipicephalus microplus is based mainly on the use of chemical acaricides, which has contributed to the emerging problem of selection of resistant tick populations. Currently, there are six main classes of acaricides commercially available in Brazil to control cattle ticks, with fluazuron, a tick growth regulator with acaricidal properties, being the only active ingredient with no previous reports of resistance. Ticks (designated the Jaguar strain) were collected in a beef cattle ranch located at Rio Grande do Sul state, Southern Brazil, after a complaint of fluazuron treatment failure. To characterise the resistance of this strain against acaricides, larval tests were performed and showed that the Jaguar strain was resistant to all of the drugs tested: cypermethrin (resistance ratio, RR=31.242), chlorpyriphos (RR=103.926), fipronil (RR=4.441), amitraz (RR=11.907) and ivermectin (3.081). A field trial was conducted to evaluate the efficacy of fluazuron treatment in heifers that had been experimentally infested with the Jaguar or a susceptible strain. Between 14 and 28 days after treatment, the average efficacy in cattle experimentally infested with the susceptible strain was 96%, while for the Jaguar strain the efficacy was zero. Additionally, the Jaguar strain response to fluazuron was evaluated in vitro using a modified adult immersion test (AIT) and the artificial feeding assay (AFA). With the AIT, 50 ppm of fluazuron inhibited 99% of larvae hatching in the susceptible strain (POA) and less than 50% in the Jaguar strain. Results of the AFA showed a larval hatching rate of 67% at 2.5 ppm of fluazuron with the Jaguar strain; conversely, only 3% of larvae of the susceptible strain hatched at the same fluazuron concentration. The results showed here demonstrated the first case of fluazuron resistance in R. microplus and the first tick population resistant to six classes of acaricides in Brazil.

Cholinesterases as markers of the inflammatory process associated oxidative stress in cattle infected by Babesia bigemina

Acaricide resistance is a major obstacle to the control of Rhipicephalus microplus. Historically, the indiscriminate use of chemical compounds has contributed to the selection of populations resistant to different classes of acaricides. Therefore, multiple acaricide resistance is an important threat to the chemical control of the cattle tick. To investigate the occurrence and extent of multiple resistance to acaricides in Southern Brazil we performed larval tests with cypermethrin, chlorpyriphos, amitraz, fipronil and ivermectin on 104 cattle tick field samples from different ranches in Rio Grande do Sul, between the years 2013 and 2015. Adult immersion tests with a commercial formulation mixture of chlorpyriphos and cypermethrin were performed on 75 samples. Four levels of resistance were established according to the mortality of larvae: Level I: mortality between 82% and 95%; Level II: mortality between 57% and 82%; Level III: mortality between 25% and 57%; and Level IV: mortality lower than 25%. Resistance to cypermethrin was detected in 98.08% of the samples evaluated, mostly at resistance level IV. The frequency of samples resistant to amitraz, chlorpyriphos, ivermectin and fipronil was 76.92%, 60.58%, 60.58% and 53.85% respectively. Multiple resistance to three or more compounds was found in 78.85% of the samples. The results obtained in this study are alarming and reveal a new scenario for the challenge of tick control using chemicals. This is an issue of high importance to cattle production systems where this tick is responsible for a high economic impact.

Borrelia burgdorferi sensu lato in Ixodes longiscutatus ticks from Brazilian Pampa

To the Editor: Several cases of tickborne rickettsiosis have been reported in South America in recent years (1,2). In Brazil, 2 spotted fever group (SFG) Rickettsia species, R. rickettsii and Rickettsia sp. strain Atlantic Rainforest, have been identified as causes of human disease. Rio Grande do Sul is the southernmost state of Brazil and the only part of the country located in the Pampa biome. Despite confirmed cases of human spotted fever in that state since 2005, little information is available regarding Rickettsia species. We report an eco-epidemiologic investigation of R. parkeri in Amblyomma tigrinum ticks on dogs from a household (and neighborhood) where a case of human spotted fever was diagnosed.