An outbreak of acute bovine mastitis caused by Klebsiella pneumoniae in a dairy herd

Descrição de um surto de mamite aguda produzida por Klebsiella pneumoniae em bovinos leiteiros

An outbreak of acute bovine mastitis caused by Klebsiella pneumoniae in a dairy herd

[Descrição de um surto de mamite aguda produzida por Klebsiella pneumoniae em bovinos leiteiros]

N. Silva, G.M. Costa

Escola de veterinária

Caixa Postal 567

30.123-970 - Belo Horizonte, Brasil

Recebido para publicação, após modificações, em 25 de maio de 2001

E-mail: [e-mail]

ABSTRACT

An outbreak of coliform mastitis is described in a dairy herd from the State of Rio de Janeiro, Brazil. During a four-month period 14 fatal cases of Klebsiella pneumoniae-related mastitis were observed in a herd of 104 lactating cows. The symptoms included peracute enterotoxemia in which the cows died 6 to 12 h after the detection of mastitis by CMT. Staphylococcus aureus and Streptococcus agalactiae Streptococcus agalactiae were also isolated although could not be associated with cases of acute fatal mastitis. Milking practices were also evaluated. The milking machine was being used correctly and adequate precautions for hygiene and pre-milking and post-milking teat dipping were used. The organism was sensitive to gentamicin. Therapy for acute toxic mastitis required early action for the treatment of infections, involving corticosteroids and fluid therapy. The use of a Klebsiella vaccine produced from the microorganisms isolated from the herd, associated with hygiene measures, resulted in the control of the outbreak.

Keywords: Dairy cow, acute bovine mastitis, outbreak, Klebsiella pneumoniae, vaccination, treatment

RESUMO

Neste trabalho está descrito um surto de mamite fatal aguda produzida por Klebsiella pneumoniae em um rebanho leiteiro, localizado no Estado do Rio de Janeiro. Durante quatro meses foram observadas 14 mortes de vacas em lactação. Os sinais clínicos observados foram de enterotoxemia aguda e as mortes ocorriam entre 6 e 12 horas após o diagnóstico de mamite por meio do California mastitis test (CMT). Outros microrganismos como Staphylococcus aureus e Streptococcus agalactiae também foram isolados, entretanto eles não foram associados aos casos agudos e fatais de mamite. O controle incluiu medidas de higiene, tratamento de casos clínicos e terapia no período seco, além da vacinação preventiva utilizando-se uma vacina produzida com amostras de K. pneumoniae isoladas do rebanho.

Palavras-Chave: Bovino, mamite aguda, surto, Klebsiella pneumoniae, vacinação, tratamento

INTRODUCTION

Environmental mastitis caused by coliforms is an economically important disease of dairy cattle. The route of entry of coliform bacteria into the mammary glands is through the streak canal and the clinical signs are associated with endotoxins released by the pathogens. The occurrence of bacteremia has been described (Cebra et al., 1996). Sometimes this disease is especially severe and can result in peracute fatalities during the immediate post-partum period (Frost & Brooker, 1986; Dejong, 1987). The success of a mastitis-control program depends on knowledge of the epidemiological aspects of the disease in the herd and especially on the identification and elimination of the primary sources of contamination (Smith et al., 1985). Some procedures were developed for coliform mastitis control and included antibiotic and fluid therapy (Christopher, 1994; Cebra et al., 1996), hygienic measures (Eberhart & Buckalew, 1977; Jones, 1990) and vaccination (Rainard & Caffin, 1983; Jones, 1990; Tyler et al., 1991). In this report it is described an outbreak of coliform mastitis in a dairy herd that resulted in the death of 14 cows and the measures used for the control.

OUTBREAK DESCRIPTION

The study involved a herd of 104 Holstein dairy cows from the State of Rio de Janeiro, Brazil, with an average milk production of 5,000kg per lactation. The control of mastitis was based on the periodic disinfection of the milking machines, pre- and post-milking teat dipping using 1% iodine-glycerine solution, and therapy of clinical cases. California mastitis test (CMT) was performed monthly and the prevalence of subclinical mastitis was about 10%. Prior to the outbreak, mastitis in the herd involved a frequency of clinical cases of 2 to 3% per month, with the isolation of Staphylococcus aureus and Streptococcus agalactiae as the agents, according to data on the farm’s recording book.

The first case of acute mastitis was observed in early October, which was followed by 24 additional cases, with 10 deaths within 30 days. In all cases, the owner had observed a mild mastitis with little, if any, systemic manifestations 12 to 24h prior to the severe acute attack. The infected quarters were treated routinely (a penicillin-streptomycin teat-infusion preparation) but without success. After that, the owner asked for technical assistance of the mastitis diagnostic laboratory at Veterinary School of Federal University of Minas Gerais. Twelve new cases occurred from November to January and four cows showing signs of peracute mastitis were investigated. Two were moribund when examined and were slaughtered immediately; the other two were examined within two hours after death. The udders of these four cows were removed, and samples were collected for bacteriological and histopathological examination.

Foremilk samples were taken from individual lactating cows for somatic cells count (SCC) (Silva et al., 1983), culture and drug sensitivity testing (Baron et al., 1990). Water samples were taken from drinking water and from udder-wash water and milking machine-wash water for bacteriological analysis (Brasil, 1981). Teat contamination by environmental pathogens was measured prior to milking, both before and after teat disinfection, using cotton wool-swabs and teat apex swabs which were immediately immersed in brain heart infusion broth (DIFCO) and refrigerated. Bacterial counts were performed in the laboratory on MacConkey agar plates (DIFCO) after incubation at 37°C for 18h.

Clinical mastitis was treated with teat infusion (250 mg/quarter) and intramuscular (2g) gentamicin every 12h during five days. Intravenous administration of a large volume of electrolytic solution (100ml/kg body weight per 24h) and corticosteroids (dexamethasone at 0.44mg/kg) were also used. Drying-off therapy was carried out with a teat infusion of gentamicin.

Mastitis control included vaccination using a bacterin in adjuvant consisting of aluminum hydroxide gel (Alu gel S, Serva) at a concentration of 4 x 10⁸ CFU/ml (colony forming units). The bacterin was manufactured with strains of K. pneumoniae isolated from the herd, according Rainard & Caffin (1983). The vaccination program started on December, and the schedule involved two doses of bacterin in all lactating cows with an interval of 30 days, and dry cows and pregnant heifers at 60 and 30 days pre-partum. Booster vaccinations were administered in all animals six months later.

RESULTS AND DISCUSSION

Previous history of mastitis in the herd was not related to the incidence of severe acute mastitis, according to farm’s recording book. Prevalence of infection as measured by an initial survey of the herd is shown in Table 1. From October to January, a higher infection level (74%) was observed in the post-partum period (1 to 100 d). Of 37 clinical cases, 14 cows died. All quarters were affected, but the rear quarters were the most frequently affected (68.8%). Foremilk samples showed somatic cells count ranging from 200,000 to 2500,000/ml. The clinical characteristics of the outbreak reported here is in agreement with descriptions for herds with experimental or natural coliform mastitis (Eberhart & Buckalew, 1977; Smith et al., 1985; Frost & Brooker, 1986; Dejong, 1987; Jones, 1990).

The anatomopathological findings on four dead cows were suggestive of endotoxin hemorrhagic lesions in the abomasal mucosa, kidneys and uterus. The mammary glands presented edema and areas of hemorrhage and infarct. Gangrenous necrosis and a blue zone were observed in two of the udders. Suprammamary lymph nodes were swollen and edematous. Degeneration of epithelial cells, hemorrhage of the subepithelium, edema, and interstitial infiltration of leukocytes were observed for the galactophorus ducts and secretory alveolus. K. pneumoniae was isolated from all of the udder samples.

Bacterial isolations from clinical mastitis and the prevalence of clinical mastitis showed that two-thirds (67.6%) of the clinical cases were caused by Gram-negative organisms. K. pneumoniae was associated with 59.5% of the cases of clinical mastitis, while co-infection with S. aureus and S. agalactiae was detected in 32.4% of cases (Table 2).

Coliform bacteria were present in water cultures at a concentration of 10⁶ CFU/ml, and K. pneumoniae was isolated from the drinking water as well as from the udder and milking machine wash water and teat apex swabs (10 to 10³ CFU/ml) suggesting that the contaminated stream water was probably the primary source of Klebsiella infection to the cows. In addition, the peak of this severe acute mastitis outbreak was in the rainy season (from October to February in Brazil). According to Thomas et al. (1982) and Hogan et al. (1989) there is a strong association between rainfall, higher incidence of K. pneumoniae in bedding material and outbreaks of Klebsiella mastitis.

Two other coliforms were also isolated from the environment and from the mammary glands (E. coli and E. aerogenes), and although not involved in peracute cases of mastitis, it is believed that they might have enhanced the pathological conditions caused by K. pneumoniae. On the other hand, S. aureus and S. agalactiae were also detected, but they were not associated with severe acute outbreaks considering that these bacteria were already prevalent in the farm, according to data on the farm’s recording book. The prevalence of subclinical mastitis produced by Gram-positive organisms increased during a three-year period (11% to 20%) as compared with the previous levels in the herd (10%). Eberhart & Buckalew (1977) described similar situation where infections produced by Gram-positive organisms were increased in herds infected by coliform organisms.

Antimicrobial sensitivity testing showed that gentamicin was the recommended antibiotic for clinical mastitis therapy in this dairy herd and treatment produced good results in this acute mastitis outbreak caused by K. pneumoniae. Twelve additional cows presenting the same clinical mastitis signs were treated with gentamicin, corticosteroids and fluid therapy and eight cows (75%) were considered recovered as clinical and bacteriological culture presented negative results. The antibiotic therapy was given by two routes (teat infusion and parenteral) considering that the distribution of drugs in a swollen udder quarter is limited. Despite the use of antibiotics for treatment of coliform mastitis has been questioned for several reasons (Pyörälä et al., 1993), the severe cases were treated prior to the appearance of severe clinical toxemia and have proven useful considering the recovery rates.

The vaccination against K. pneumoniae was used as an approach to prevent new coliform mastitis cases (Table 3). Although the capsular types of K. pneumoniae were not determined, different strains could be present due the different antibiotic sensitivity patterns presented by all isolated strains. The vaccination of cows was recommended during the dry period and at calving to reduce the incidence of naturally occurring clinical coliform mastitis. A reduction in the occurrence of clinical coliform mastitis cases (only 10 news cases of Klebsiella mastitis with little if any systemic manifestations) was noted following this approach in comparison to the previous approaches and no deaths occurred after the vaccination program started. Vaccination apparently enhanced host defenses and bacteria were probably eliminated from the mammary gland without signs being detected. In this outbreak the vaccination was used as an important tool for control, although may not be recommended for the control of coliform mastitis cases as a single measure.

Mastitis research generally concentrates on the various aspects of the non-fatal forms of the disease. The severity of the outbreak reported here, however, which included fatalities after only a very short period of clinical symptoms, demonstrates the importance of mastitis caused by K. pneumoniae.

REFERENCES

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Publication Dates

• Publication in this collection
  20 June 2002
• Date of issue
  Aug 2001

History

• Received
  25 May 2001