On the etiology of an outbreak of winter dysentery in dairy cows in Brazil

摘要

Winter dysentery (WD) is a seasonal infectious disease described worldwide that causes a marked decrease in milk production in dairy cows. In the Northern hemisphere, where the disease is classically recognized, bovine coronavirus (BCoV) has been assigned as a major etiologic agent of the disease. Nonetheless, in the Southern hemisphere, an in-deep etiological survey on WD cases had not been carried out. This study aimed to survey for BCoV by nested-RT-PCR, rotavirus by polyacrylamide gel electrophoresis (PAGE) and ELISA, bacteria by classical bacteriological methods and PCR for virulence factors and parasites by sugar flotation test on fecal samples of 21 cows from a farm during an outbreak of WD in São Paulo state, Southeastern Brazil. BCoV was detected in all 21 samples, while rotavirus was detected in two symptomatic cows. Escherichia coli, Yersinia intermedia, Providencia rustigianii Proteus penneri, Klebsiella terrigena and Enterobacter aglomerans were detected in samples from both asymptomatic and healthy cows in different associations. The study of E. coli virulence factors revealed that the strains isolated were all apathogenic. Cysts of Eimeria sp. and eggs of Strongyloidea were detected at low numbers in four of the symptomatic cows, with one co-infestation. These results suggest BCoV as the main etiologic agent of the cases of WD in Brazil, a conclusion that, with the clinical and epidemiological patterns of the disease studied herein, match those already described elsewhere. These findings give basis to the development of preventive measures and contribute to the understanding of the etiology of WD. Index terms: Bovine coronavirus, etiology, winter dysentery. RESUMO Em vacas leiteiras, a disenteria de inverno (DI) é uma doença infecciosa sazonal mundialmente relatada que ocasiona uma marcada queda na produção de leite; no hemisfério Norte, onde a doença é classicamente reconhecida, o coronavirus bovino (BCoV) tem um importante papel como agente etiológico. Entretanto, no hemisfério Sul, pesquisas etiológicas aprofundadas em casos de DI nunca forma realizadas. Este estudo objetivou a pesquisa de BCoV utilizando nested-RT-PCR, rotavírus utilizando eletroforese em gel de poliacrilamida (PAGE) e ELISA, bactérias com métodos bacteriológicos clássicos e PCR para fatores de virulência e parasitas pela técnica de flutuação em açúcar em 21 amostras fecais de vacas de uma fazenda durante um surto de DI no estado de São Paulo, Sudeste do Brasil. BCoV foi encontrado em todas as 21 amostras, enquanto que rotavírus foi encontrado em duas vacas sintomáticas. Escherichia coli, Yersinia intermedia, Providencia rustigiani, Proteus penneri, Klebsiella terrigena e Enterobacter aglomerans foram encontradas tanto em amostras de vacas sintomáticas quanto assintomáticas. O estudo de fatores de virulência para E. coli revelou que as amostras isoladas eram todas apatogênicas. Cistos de Eimeria sp. e ovos de Strongyloidea foram encontrados em baixos números em quatro animais sintomáticos, com uma co-infestação. Tais resultados sugerem o BCoV como o principal agente etiológico em casos de DI no Brasil, uma conclusão que, somada aos padrões clínicos e epidemiológicos da doença aqui estudada, concordam com aqueles descritos em outras regiões. Estes achados fornecem base o desenvolvimento de medidas preventivas e também contribuem para o entendimento sobre a etiologia da DI. Termos de indexação: Coronavírus bovino, disenteria de inverno, etiologia.     INTRODUCTION Winter dysentery (WD) is an acute epizootic infectious disease with a seasonal occurence and worldwide distribution that affects adult cattle, with a higher prevalence amongst dairy cows. The disease has already been associated with bovine coronavirus (BCoV), torovirus, rotavirus, bovine viral diarrhea virus, Salmonella sp., Crysptosporidium parvum and Eimeria bovis (Campbell & Cookingham 1978, Koopmans et al. 1991). The disease was formally first described by Horner et al. (1975) and has already been reported in countries such as France, Sweden, Korea, Japan, Canada, USA and Brazil (Jactel et al. 1990, Alenius et al. 1991, Milane et al. 1995, Fukutomi et al. 1999, Cho et al. 2000, Brandão et al. 2002, Jeong et al. 2005). The yearly outbreaks may last up to 10 days, the symptoms starting during the winter months, initially in a small number of cows. In a few days, up to 100% of the herd may be affected with acute and severe dysentery, which might be bloody, with the excretion of large amounts of enteric tissue, depressed body condition, dehydratation and marked decrease in milk production (Tråven et al. 2001). Though often reported in da