Prevalence of Streptococcus equi subsp. equi in horses and associated risk factors in the State of Rio Grande do Sul, Brazil

doi:10.1016/j.rvsc.2015.11.009

Research in Veterinary Science

Volume 104, February 2016, Pages 53-57

https://doi.org/10.1016/j.rvsc.2015.11.009 Get rights and content

Highlights

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S. equi in healthy horses is distributed across the whole state of Rio Grande do Sul.
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Associated factors for strangles are related with farm management practices.
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Associated factors identified in this study were: group events, sharing of food containers, and positive diagnosis of strangles on the farm.
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The results provide epidemiological contribution to strangles control.

Abstract

The aim of this study was to estimate the prevalence of equine strangles and to identify associated risk factors for this disease through a cross-sectional study of nasal swabs. Nasal swabs (n = 1010) from healthy equines (absence of nasal discharge, lymphadenopathy and cough) from 341 farms were plated on 5% blood agar; of these horses, 24 were identified as positive for Streptococcus equi through isolation, PCR and DNA sequencing. The estimated prevalence for individual animals was 2.3%, and for herds, it was 5.86%. Statistical analysis identified the following as associated risk factors: the number of group events that were attended by the equines (PR: 1.06); the sharing of food containers (PR: 3.74); and at least one previous positive diagnosis of strangles on the farm (PR: 3.20). These results constitute an epidemiological contribution to the horse industry and may support measures for the future control of the disease.

Introduction

Streptococcus equi subsp. equi (S. equi) is a Gram-positive, encapsulated coccus that is included in the β-hemolytic group C of Lancefield (Quinn et al., 2011). This pathogen is the etiologic agent of equine strangles, which is an acute, highly contagious infectious disease that affects equids worldwide. Strangles is characterized by purulent inflammation of the upper respiratory tract of horses (Schild, 2001). This disorder presents with increased volumes of the retropharyngeal and submandibular lymph nodes, which obstruct the pharynx and cause significant harm to the animal's performance. Strangles also causes empyema of the guttural pouches (Anzai et al., 1999).

S. equi infection occurs through inhalation and/or ingestion of the microorganism, followed by its fixation in the nasopharyngeal epithelium and migration to the regional lymph nodes (Timoney, 2004). The main clinical signs of strangles are fever, runny nose and abscessation of the lymph nodes (Sellon, 2013).

Outbreaks of strangles result from predisposing factors such as the stress of weaning, abrupt climate change, concomitant disease, overcrowding, nutritional deficiency, parasites, animal handling (high concentration of animals in one place) and the breeding season, a period when animals of different origins are grouped (Moraes et al., 2009, Oikawa et al., 1995). Yearling horses are the most prone to develop strangles, followed by weaned foals and adults (Yelle, 1987).

Studies of the prevalence and incidence rates of S. equi as well as of risk factors for the development of equine strangles are very rare in the literature. To date, Clark et al. (2008) reported positivity by isolation (18.4%) in samples collected from guttural pouches, and AL-Ghamdi (2012) reported 28% of horses as seropositive. Thus, the aim of this study was to determine the prevalence of S. equi at the animal and herd levels as well as to identify risk factors related to equine strangles through a cross-sectional study based on nasal swab samples.

Section snippets

Study area and target population

The State of Rio Grande do Sul (RS), located in Brazil's southern region, has an area of 268,782 km² (3.16% of the country) and is bordered by two countries, namely Argentina and Uruguay (Fig. 1). The state is divided into seven regions; these regions serve to group various counties according to proximity and common agroecological characteristics (Fig. 1).

According to the official data from the Secretary of Agriculture, Livestock and Agribusiness of the State of Rio Grande do Sul (SEAPA-RS), ~

S. equi prevalence

Of all of the samples collected from the 341 farms, 1010 nasal swabs were examined for the presence of S. equi. Of these 341 farms, 91.47% had 1 to 10 animals. A total of 24 equines were positive. Therefore, at the animal level, the estimated prevalence of S. equi was 2.37% (CI_95%: 1.43%-3.31%). At the herd level, twenty farms were considered positive (5.86%; CI_95%: 3.37%-8.35%) (Table 1). There were no differences in the proportions of positive farms and animals between the regions (Table 1).

Risk factor analysis

Discussion

To the best of our knowledge, the prevalence of S. equi based on a probabilistic sample as well as the identification of associated risk factors for equine strangles have not yet been reported. Although positivity rates have been reported for equine establishments in Japan (Anzai et al., 1997), Canada (Clark et al., 2008), Saudi Arabia (Al-Ghamdi, 2012), and Brazil (Libardoni et al., 2013), these studies did not utilize a sampling design that allowed inferences to be drawn regarding

Conclusions

This investigation revealed isolates of S. equi on farms that lacked current strangles. At the farm level, the presence of the infection was related to the number of events to which the horse owner had taken the animals, the sharing of food containers and a previous incidence of strangles. This study provides information that will enable better discussions of the prevalence of S. equi because it was performed based on a probabilistic sample, which is noticeably lacking in the current disease

Acknowledgments

We thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq/Brazil), Fundo Estadual de Sanidade Animal do Rio Grande do Sul (FUNDESA-RS), and all of the official veterinarians of the Departamento de Defesa Agropecuária of Secretaria de Agricultura Pecuária e Agronegócio (veterinarians and their assistants) who carried out the sampling and administered questionnaires in the field, in addition to the Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS).

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Strangles, caused by Streptococcus equi subspecies equi, is a highly infectious respiratory disease affecting horses and other equines. The disease is economically important and compromises the productivity of equine farm significantly. The disease is characterized by pyrexia, mucopurulent nasal discharge, and abscess formation in the lymph nodes of the head and neck of horses. The disease transmission occurs either directly by coming in contact with infectious exudates or indirectly via fomite transmission. Besides this, carrier animals are the primary and most problematic source of disease infection. The organism not only initiates outbreaks but also makes the control and prevention of the disease difficult. The diagnosis of strangles is best done by isolating and characterizing the bacteria from nasal discharge, pus from abscesses, and lymphoid tissues or by using PCR. ELISA can also be used to detect serum protein M (SeM) antibodies for diagnosis. The most popular treatment for strangles is with penicillin; however, the treatment is affected by the stage, feature and severity of the disease. Prevention and control of strangles can be achieved through vaccination and good hygiene practices. Basically, this review describes the global prevalence of S. equi, as well as general aspects of the disease, like pathogenesis, diagnosis, treatment, prevention, control and management of the disease.
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Besides, 11 (1.09%) profiles had negative growth, while 88 (8.71%) showed mixed or contaminated cultures. Twenty-four of the 157 Streptococcus spp. found in this evaluation were further identified as Streptococcus equi equi [13], and 10 of the 41 Actinomycetales were further identified as Rhodococcus equi [7]. In India, R. equi was isolated from 2.57% of apparently healthy horses used in tourism, while S. equi equi was not registered [14].
Microbiological diagnosis of equine respiratory infections is essential for disease management. However, reliable diagnosis can be a challenge due to colonization of the upper respiratory tract (URT) by a diverse microbial population, and because there is a lack of studies with samples from healthy animals. Aiming to guide adequate URT culture, this work reports culturable microbial population from the URT of 1,010 apparently healthy horses from 341 farms in Southern Brazil and identifies the putative presence of pathogenic microorganisms. Nasal swabs were cultured in 5% blood agar, and the isolates were phenotypically identified to genus level. A diverse respiratory microbial population was found, mostly composed of Gram-positive bacteria, including Staphylococcus spp., Bacillus spp., Streptococcus spp. and Corynebacterium spp. The microbiological profile from the nasal cavity of 911 horses was described, with the five most common profiles being: (1) Staphylococcus sp. + Gram-negative bacilli (12.67%), (2) Staphylococcus sp. in pure culture (12.47%), (3) Staphylococcus sp. + Bacillus sp. (10.10%), (4) Gram-negative bacilli in pure culture (6.93%), and (5) Staphylococcus sp. + Bacillus sp. + Gram-negative bacilli (6.73%). Streptococcus equi equi and Rhodococcus equi were detected in 34 horses (3.37%), demonstrating the presence of pathogenic bacteria along with commensal microorganisms in apparently healthy animals. The disclosed data may guide and facilitate microbiological diagnosis of URT infection in horses. The significant presence of Gram-negative bacilli was evidenced, as well as the occurrence of relevant pathogens, such as S. equi equi and R. equi, thus helping to improve diagnosis and antimicrobial therapy.
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An observational cross-sectional study was conducted from December 2017 to December 2018. The sample size was calculated according to the population of horses in the municipality (3,000), an error rate of 5%, a 10% expected prevalence [8,9] and with a confidence level of 95%. Based on these calculations using Epi Info, a required sample size of 137 Paso Fino horses was determined.
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Prevalence of Streptococcus equi subsp. equi in horses and associated risk factors in the State of Rio Grande do Sul, Brazil

Highlights

Abstract

Introduction

Section snippets

Study area and target population

S. equi prevalence

Risk factor analysis

Discussion

Conclusions

Acknowledgments

Vet. Immunol. Immunopathol.

Vet. Microbiol.

J. Comp. Pathol.

Vet. J.

Serology study of Streptococcus equi in Saudi Arabia

Vet. Res.

Equine infectious anemia: prevalence in working equids of livestock herds, in Minas Gerais, Brazil

Arq. Bras. Med. Vet. Zootec.

Isolation of Streptococcus equi subsp. equi from thoroughbred horses in a racehorse-breeding area of Japan

J. Vet. Med. Sci.

Bacterial isolates from equine infections in western Canada (1998–2003)

Can. Vet. J.

The use of confidence or fiducial limits illustrated in the case of the binomial

Biometrika