4 minute read
Hyper-Immune Plasma Could Decrease R. equi Fecal Shedding
By Marie Rosenthal, MS
The administration ofRhodococcus equi specific pneumonia until about 3 months old or so, but they hyper-immune plasma (Re-HIP) to neonatal foals debecome infected with the bacteria early in life, likely creases fecal shedding, lowering environmental conwithin the first few weeks of life, according to Dr. Sanz, DVM, PhD, DACVIM, assistant professor of equine medicine of Washington State University in Pullman.
“I think it's a beneficial effect of this plasma that nobody has looked at before,” she said at the American Association of Equine Practitioners 65th Annual Convention.
R. equi grows slowly, so many foals do not develop pneumonia until about 3 months old or so, but they become infected with the bacteria early in life, likely within the first few weeks of life, according to Dr. Sanz, and easily shed the bacteria in their feces, contaminating the environment and infecting other foals.
Highly Infectious
“We are very well aware that foals are getting infected with these bacteria pretty much as they hit the ground,” she said. “So that first week or 2 is extremely important.”
Dr. Sanz and her colleagues’ previous work, while at the Gluck Research Institute, showed that foals given Re-HIP within 24 hours of experimental infection were less likely to develop severe pneumonia if challenged with R. equi that had the vapA gene, because that is the strain that causes pathogenesis.
Virulent Bacteria
“VapA is what makes Rhodococcus pathogenic,” Dr. Sanz explained. “In the environment there are multiple strains of Rhodococcus, but the one that will cause disease is the one that carries the vapA gene.”
They thought about that result and wanted to know if they could take it one step farther, if the foals were given Re-HIP prophylactically and this lowered the clinical pneumonis, would it lower the fecal shedding of these experimentally infected foals?
“I looked back at this study and tried to put 2 and 2 together. I started thinking: if the plasma decreases the severity of pneumonia and these pneumonic foals are the foals that contaminate the environment would the administration of plasma lower that [shedding],” she said. “We thought decreased pneumonia would result in a reduced shedding of pathogenic R. equi.”
They separated research foals into two groups: 12 received Re-HIP and 9 foals did not. Then they challenged them with R. equi that they knew contained the vapA gene, and therefore, was more likely to cause disease in the foals.
All of the foals that received Re-HIP received the plasma within 48 hours of birth; some within 24 hours. The horses were experimentally challenged with pathogenic R. equi that was placed in their trachea during the first week of life.
“We sedated them, put the Rhodococcus down their trachea, and then we monitored the foals weekly,” she said, adding that very little bacteria were needed to infect the foals because the organism is so virulent. In addition, they collected fecal samples right before infection and then 2, 3, 5 and 7 weeks after they were challenged with the bacteria.
They tested the 101 fecal samples by quantitative PCR; 20 prechallenge and 81 post challenge. They found 11 out of 81 samples were positive for the vapA gene. Most of the positives were from the control group: 9 versus only 2 from the treatment group, she said, which was statistically significant (P=0.031)
“So we found a fairly strong association between the administration of plasma, and this decrease of fecal shedding, and that was statistically significant,” Dr. Sanz said.
“The other thing we found is the administration of hyper-immune plasma decreased the amount of virulent bacteria [shed during the study],” she added.
Typically with this experimental model about half of the challenged foals would go on to develop clinical pneumonia, she said, which was pretty close to the number of penumonias in the control group. Among the control group, 4 out of 9 developed pneumonia; and only 2 out of 12 developed pneumonia in the Re-HIP group.
“So the plasma was very protective for pneumonia in our study,” she said. “They still developed clinical pneumonia, but it was a lot less severe,” she said, and as a result, there was less R equi shedding.
As in any study, there were limitations she admitted, mostly that the animals were experimentally infected vs. animals that are infected naturally.
The study was funded by the Advancement in Equine Research Award, Boehringer Ingelheim.
For more information:
Sanz MG, Bradway DS, Horohoy DW, et al. Rhodococcus equi-specific hyperimmune plasma administration decreases faecal shedding of pathogenic R. equi in foals. Vet Rec. 2019 Jul 6;185(1):19. doi: 10.1136/vr.105327. Epub 2019 Apr 17. https://pubmed.ncbi.nlm.nih.gov/30995996/?from_term=Sanz+MG+and+Rhodococcus&from_pos=2
Sanz MG, Oliveira AF, Loynachan A, et al. Validation and evaluation of VAPA-specific IgG and IgG subclass enzyme-linked immunosorbent assays (ELISAs) to identify foals with Rhodococcus equine pneumonia. Equine Vet J. 2016 Jan;48(1):103-108. https://pubmed.ncbi.nlm.nih.gov/25257622/?from_term=Sanz+MG+and+equine&from_pos=3
