New route of infection found for common horse bacterium

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Lesions caused by spontaneous infection of alpacas by Streptococcus equi subspecies zooepidemicus. Figure 1. Fibrinous peritonitis (arrow) in mildly icteric carcass of case 2. Figure 2. Fibrinosuppurative pleuritis in case 2. H&E. Insert: myriad gram-positive cocci in the pleura. Gram stain. Figure 3. Diffuse congestion, alveolar edema, hemorrhage, and colonies of cocci in the lung in case 2. H&E. Insert: colonies of gram-positive cocci in alveolar space and interstitium. Gram stain. Figure 4. Small intestinal transmural pleocellular enteritis, including submucosal and serosal edema, hemorrhages, and mesenteric thrombi with cocci in blood and lymphatic vessels (asterisks) in case 1.

Evidence has emerged that the bacterium Streptococcus equi subspecies zooepidemicus is able to spread through the lymphatic system and not just blood vessels.

S. equi ssp. zooepidemicus is the bacterium most frequently isolated from the respiratory tract of clinically healthy horses, and horses with pneumonia.

It is an opportunistic pathogen, associated with multiple syndromes in several animal species.

In horses, it can give rise to respiratory infections in young horses and uterine infections in elderly mares.

In dogs, it can cause fever, breathlessness, bleeding and fluid build-up in the lungs, and death.

It can infect camels, ruminants, pigs, humans and non-human primates.

In alpacas, it can cause a nasty condition called alpaca fever, which can lead to death.

Juan Corpa, a professor at Cardenal Herrera University in Valencia, Spain, joined with researchers in California to learn more about alpaca fever.

The study team, writing in the Journal of Veterinary Diagnostic Investigation, described for the first time, a new route of infection for the bacterium.

Professor Corpa and researchers from the University of California, Davis, concluded that the spread of this bacterium can take place not only through blood vessels, as was believed until now, but also through lymph vessels. It can invade the digestive system of some infected animals through this route.

“This subspecies of the Streptococcus equi bacteria is typically found in the respiratory system of healthy horses and those with pneumonia, and has also been associated with numerous syndromes in different animal species such as dogs, camelids, ruminants, pigs and primates,” Corpa explains.

“Similarly, infections from this bacterium have also been documented in people that were in close contact with horses, which is why it is said to be zoonotic. In other words, that it can transfer from animals to humans.”

Corpa, who collaborated with researchers from the California Animal Health and Food Safety System in the study, investigated three alpacas who had been naturally infected by the bacterium. In all three cases, the infection proved fatal.

Alpacas with this disease can also infect people who come into contact with these animals.

“When humans become infected with this bacterium, mainly due to the contact with horses, they can sometimes develop severe diseases such as meningitis, endocarditis, aortic aneurisms, thrombosis, spondylodiscitis, etc,” Corpa says.

“In the most extreme cases, these infections can cause death. This is why the disease is considered a budding zoonosis, which can affect people who are in close contact with these animals.”

The study team comprised Corpa, Francisco Carvallo and Francisco Uzal, of the San Bernardino laboratory of the California Animal Health and Food Safety (CAHFS) System, from the School of Veterinary Medicine of the University of Davis, in California (USA).

Corpa JM, Carvallo F, Anderson ML, Nyaoke AC, Moore JD, Uzal FA. Streptococcus equi subspecies zooepidemicus septicemia in alpacas: three cases and review of the literature. J Vet Diagn Invest. 2018;30(4):598-602. doi: 10.1177/1040638718772071.

The study can be read here

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