Background: Transfusion of plasma hyperimmune against Rhodococcus equi (REHIP) is used to reduce the incidence of foal pneumonia caused by R. equi on endemic farms, but the optimal volume to transfuse is unknown. Objectives: To determine whether transfusion of 2 L of REHIP to foals was superior to transfusion of 1 L for reducing the incidence of pneumonia attributed to R. equi in foals. Study design: Retrospective cohort design. Methods: Medical records of 158 foals from two breeding farms in Saratoga Springs, New York, were reviewed. Information collected from mares and foals included the date of birth, volume of REHIP transfused to foals, and whether the foal developed pneumonia attributed to R. equi. Data were analysed using random-effects logistic regression with pneumonia as the outcome variable and farm modelled as a random effect to account for clustering of foals within farm. Results: There were 77 foals with evidence of clinical (n = 75) or subclinical (n = 2) pneumonia. The odds of pneumonia were 2.5-fold greater (95% confidence interval [CI], 1.1-5.8; P = 0.0319) for foals transfused with 1 L than for foals transfused with 2 L. The odds of pneumonia were 2.7-fold (95% CI, 1.4-5.5; P = 0.0046) greater for foals born in April or May than for foals born before April. Accounting for the effects of birth month, the odds of pneumonia were 2.4-fold (95% CI, 1.1-5.6; P = 0.0457) higher for foals transfused with 1 L of REHIP than for foals transfused with 2 L. Main limitations: The major limitations of this study are the observational study design and that diagnosis of R. equi pneumonia was presumptive. Conclusions Transfusing foals with 2 L of REHIP is probably superior to transfusing 1 L for reducing the incidence of R. equi pneumonia and appeared safe.• Transfusion of 2 L to foals appeared to be safe and effective.• Many farms probably under-dose plasma when transfusing foals to prevent R. equi pneumonia.• Odds of R. equi pneumonia are greater for foals born in later months at farms in North America.
Background
The bacterium
Rhodococcus equi
can cause severe pneumonia in foals. The absence of a licensed vaccine and limited effectiveness of commercial
R. equi
hyperimmune plasma (RE‐HIP) create a great need for improved prevention of this disease.
Hypothesis
Plasma hyperimmune to the capsular polysaccharide poly‐
N
‐acetyl glucosamine (PNAG) would be significantly more effective than RE‐HIP at mediating complement deposition and opsonophagocytic killing (OPK) of
R. equi
.
Animals
Venipuncture was performed on 9 Quarter Horses.
Methods
The ability of the following plasma sources to mediate complement component 1 (C1) deposition onto either PNAG or
R. equi
was determined by ELISA: (1) PNAG hyperimmune plasma (PNAG‐HIP), (2) RE‐HIP, and (3) standard non‐hyperimmune commercial plasma (SP). For OPK, each plasma type was combined with
R. equi
, equine complement, and neutrophils isolated from horses (n = 9); after 4 hours, the number of
R. equi
in each well was determined by quantitative culture. Data were analyzed using linear mixed‐effects regression with significance set at
P
< .05.
Results
The PNAG‐HIP and RE‐HIP were able to deposit significantly (
P
< .05) more complement onto their respective targets than the other plasmas. The mean proportional survival of
R. equi
opsonized with PNAG‐HIP was significantly (
P
< .05) less (14.7%) than that for SP (51.1%) or RE‐HIP (42.2%).
Conclusions and Clinical Importance
Plasma hyperimmune to PNAG is superior to RE‐HIP for opsonizing and killing
R. equi
in vitro. Comparison of these 2 plasmas in field trials is warranted because of the reported incomplete effectiveness of RE‐HIP.
Honokiol, a highly functional phenolic- and alkenyl-containing neolignan natural product isolated fromMagnoliaplants, is an interesting bio-based resource which is shown to be useful as a monomer for the synthesis of poly(honokiol carbonate) (PHC).
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