Longitudinal study of risk factors for anaplasmosis and transplacental transmission in herd cattle

Abstract

Anaplasma marginale, bacteria that occurs in tropical and subtropical areas throughout the world, is responsible for causing a disease that is one of the most constraint to cattle production in many countries. The present work aimed to investigate potential risk factors for anaplasmosis and the occurrence of transplacental transmission by molecular and serological assays in cattle. A total of 22 calves were randomly sampled and monitored during four years; the presence of infection/exposure to A. marginale was assessed by a semi-nested PCR assay targeting msp-5 gene of A. marginale, indirect ELISA for detection of IgG antibodies to A. marginale and blood smears. The A. marginale infection prevalence data were analyzed in relation to risk factors, using chi-squared, odds ratio and multiple logistic regressions. DNA amplification results revealed a frequency of infection with A. marginale of 41% (9/22) in the newborn calves before colostrum suckling. However, only 14% (3/22) of newborn calves were seropositive for A. marginale. All calves were positive to A. marginale by PCR and microscopic examination of blood smears before the two and fourth month of age, respectively. The main risk factors associated with seroprevalence were breed (OR=36.2), tick infestation (OR=3.44) and stocking density (OR=3.28). The results indicated that exposure of cattle to A. marginale was common in dairy herds and endemic instability situation probably is due to inadequate antibody production in cows or genetic variability of pathogen. This study still demonstrated that in addition to transmission of A. marginale by ticks and flies, the transplacental transmission is very important and should be the target of disease control programs in Brazil. Key words: Anaplasma marginale, blood smear, ELISA, PCR ResumoAnaplasma marginale, bactéria que ocorre em regiões tropicais e subtropicais do mundo, é responsável por causar uma das doenças que mais restringem a criação de bovinos em diversos países. O presente trabalho teve como objetivo investigar potenciais fatores de risco para a anaplasmose e a ocorrência de transmissão transplacentária por ensaios moleculares e sorológicos em bovinos. (OR = 3,28). Os resultados indicaram que a exposição de gado para A. marginale era comum nos rebanhos leiteiros e a situação de instabilidade endêmica provavelmente se faz devido à produção inadequada de anticorpos em vacas ou a variabilidade genética do patógeno. Este estudo demonstra ainda que, além da transmissão de A. marginale por carrapatos e moscas, a transmissão transplacentária é muito importante e deve ser alvo de programas de controle da doença no Brasil.

Revisão sistemática sobre diagnóstico molecular da tristeza parasitária bovina no Brasil: ocorrência e oportunidades futuras

“…Molecular biology techniques, which offer higher sensitivity and specificity, help overcome limitations associated with other diagnostic tools, such as false positives due to staining artifacts in blood smears (Silaghi et al, 2017). By using quantitative and semiquantitative PCR, it is possible to identify not only the parasite involved but also the intensity of the infection (Silva et al, 2014). Nevertheless, due to the more complex procedures and higher costs associated with molecular techniques, several studies in Brazil have explored infections by Babesia spp.…”

“…The ability of the pathogens to evade the immune system of the host means that treatment does not always completely eliminate the parasites, and animals can become persistently infected (reservoirs). These parasites remain latent in bovine cells (Kieser et al, 1990;Yokoyama et al, 2006), with potential for parasitemia resurgence during stressful situations, such as transport, high population density, and peripartum, leading to acute disease outbreaks (Silva et al, 2014).…”