Emerging pathogen in humans linked to pneumonia in a horse

Researchers believe it is the first time Klebsiella variicola has been identified as the cause of respiratory disease in a horse.
Researchers believe it is the first time Klebsiella variicola has been identified as the cause of respiratory disease in a horse.

A bacterium considered an emerging pathogen in humans has been linked to a serious lung infection in a horse in Italy.

The details of the horse’s illness are described in a case report just published in the journal BMC Veterinary Research.

The 17-year-old saddle horse was found to be infected with Klebsiella variicola. The researchers believe it is the first time K. variicola has been identified as the cause of respiratory disease in a horse.

The bacterium was first isolated in Mexico in 2004, initially being identified as an endophyte in soil and plants such as bananas, rice, sugar cane and maize.

However, recent studies have identified the micro-organisim as an emerging pathogen in humans.

“It has been isolated from many clinical samples, including blood, tracheal aspirates, several types of secretions as well as the respiratory and urinary tract,” Elisabetta Mondo and her colleagues at the University of Bologna noted.

In animals, species of Klebsiella are associated with infections of the urinary tract, respiratory tract and sepsis, while Klebsiella variicola has to date been described only in bovine mastitis.

The horse at the center of the case study was admitted to the university’s Veterinary Teaching Hospital, part of the Department of Veterinary Medical Sciences. It was laboring under respiratory distress and had a fever.

At home, the horse had undergone antibiotic therapy without improvement.

Vital signs on admission revealed an increased respiratory rate, a racing heart, a fever, and weight loss.

Testing revealed a bilateral seropurulent pleural effusion — pus and fluid on both lungs — with associated areas of collapsed lung.

A sample of the fluid — a cloudy yellow colour — was collected, with testing identifying the presence of K. variicola.

The isolate was found to be sensitive to several antimicrobials — amikacin, cefazolin, enrofloxacin, marbofloxacin, tetracycline, and trimethoprim-sulfamethoxazole.

The horse was treated with oxytetracycline and amikacin, and a tube was inserted in the chest so the fluid could be drained daily.

Despite general health improvement in the horse, and its discharge home, it still retained some fluid on the lung 10 weeks later.

The authors noted the similarities between K. pneumoniae and K. variicola, leading to potential misidentification. Indeed, several researchers have estimated that around 10% of K. pneumoniae isolated in human infections are actually misidentifications of K. variicola.

There is also evidence that K. variicola is more virulent than K. pneumoniae, which is among a range of pathogens capable of causing viral pneumonia in horses.

“Correct identification of K. variicola is of the utmost importance because this new bacterium may be a pathogenic agent in the animals like it is classified as an important human pathogen,” the study team wrote.

Correct identification will also aid in the use of appropriate antimicrobial therapies, which is fundamental for the animal’s healing and the prudent use of antibiotics.

“In line with our findings, K. variicola isolates are broadly antimicrobial susceptible and have lower antibiotic resistance rates than other Klebsiella species. Nevertheless, lower antibiotic resistance rates do not necessarily correlate with better treatment outcomes in K. variicola infections.

“Further efforts should be performed to differentiate K. variicola from K. pneumoniae complex since adequate identification of K. variicola is not routinely performed in clinical specimens and its real incidence is unknown.

“The use of new methods for bacterial identification will probably lead to the isolation of a greater number of strains that will widen knowledge on the pathogenic power and diffusion, as well as on the clinical importance and relevance of K. variicola in human and animal infection.”

The authors suggest that misidentification between K. pneumoniae and K. variicola has probably reduced awareness about the latter and its possible role in diseases in animals.

“Probably due to the poor isolation rate, its role is not clear in animals, while it has been demonstrated to be an emerging human pathogen.

“Further studies will be needed to understand the spread and the virulence pattern of K. variicola in veterinary medicine.”

The University of Bologna study team comprised Mondo, Riccardo Rinnovati, Alessandro Spadari, Federica Giacometti, Andrea Serraino, Federica Savini and Silvia Piva.

Mondo, E., Rinnovati, R., Spadari, A. et al. First isolation of Klebsiella variicola from a horse pleural effusion. BMC Vet Res 17, 75 (2021). https://doi.org/10.1186/s12917-021-02776-2

The case report, published under a Creative Commons License, can be read here.

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