Serum activities of complement 1q and antibodies to the virulence-associated protein A are lower in foals that develop rhodococcal pneumonia.

Objective: To determine the effects of transfusion of Rhodococcus equi hyperimmune plasma (REHIP) on serum concentrations of complement component 1q (C1q) and to examine the association of serum C1q and anti-rhodococcal antibodies of newborn foals with subsequent development of rhodococcal pneumonia.

Animals/samples: Foals (n = 205) from 2 Thoroughbred breeding farms in New York transfused with REHIP between January 1, 2022, and December 1, 2022.

Procedures: Blood was collected immediately before transfusion with REHIP and again from the contralateral vein immediately after transfusion.

Intramuscular but not nebulized administration of a mRNA vaccine against Rhodococcus equi stimulated humoral immune responses in neonatal foals.

Objective: Design and evaluate immune responses of neonatal foals to a mRNA vaccine expressing the virulence-associated protein A (VapA) of Rhodococcus equi.

Animals: Cultured primary equine respiratory tract cells; Serum, bronchoalveolar lavage fluid (BALF), and peripheral blood mononuclear cells (PBMCs) from 30 healthy Quarter Horse foals.

Methods: VapA expression was evaluated by western immunoblot in cultured equine bronchial cells transfected with 4 mRNA constructs encoding VapA.

Transfusion of hyperimmune plasma for protecting foals against Rhodococcus equi pneumonia.

The bacterium Rhodococcus equi causes pneumonia in foals that is prevalent at breeding farms worldwide. In the absence of an effective vaccine, transfusion of commercial plasma from donor horses hyperimmunised against R. equi is used by many farms to reduce the incidence of pneumonia among foals at farms where the disease is endemic.

Fecal concentration of Rhodococcus equi determined by quantitative polymerase chain reaction of rectal swab samples to differentiate foals with pneumonia from healthy foals.

Background: Diagnostic accuracy of real-time, quantitative PCR (qPCR) assays to quantify virulent Rhodococcus equi using rectal swab samples has not been systematically evaluated.

Objective: To evaluate the accuracy of qPCR of rectal swab samples to differentiate foals with pneumonia from healthy foals of similar age from the same environment.

Animals: One hundred privately owned foals born in 2021 from 2 farms in New York.

Association of pneumonia with concentrations of virulent Rhodococcus equi in fecal swabs of foals before and after intrabronchial infection with virulent R. equi.

Background: Intragastric administration of virulent Rhodococcus equi protects foals against subsequent experimental intrabronchial (IB) infection, but it is unknown whether R. equi naturally ingested by foals contributes to their susceptibility to pneumonia.

Hypothesis: Fecal concentration of virulent R.

Antibody activities in hyperimmune plasma against the Rhodococcus equi virulence -associated protein A or poly-N-acetyl glucosamine are associated with protection of foals against rhodococcal pneumonia.

The efficacy of transfusion with hyperimmune plasma (HIP) for preventing pneumonia caused by Rhodococcus equi remains ill-defined. Quarter Horse foals at 2 large breeding farms were randomly assigned to be transfused with 2 L of HIP from adult donors hyperimmunized either with R. equi (RE HIP) or a conjugate vaccine eliciting antibody to the surface polysaccharide β-1→6-poly-N-acetyl glucosamine (PNAG HIP) within 24 hours of birth.

Serum Antibody Activity against Poly--Acetyl Glucosamine (PNAG), but Not PNAG Vaccination Status, Is Associated with Protecting Newborn Foals against Intrabronchial Infection with Rhodococcus equi.

Rhodococcus equi is a prevalent cause of pneumonia in foals worldwide. Our laboratory has demonstrated that vaccination against the surface polysaccharide β-1→6-poly--acetylglucosamine (PNAG) protects foals against intrabronchial infection with when challenged at age 28 days. However, it is important that the efficacy of this vaccine be evaluated in foals when they are infected at an earlier age, because foals are naturally exposed to virulent in their environment from birth and because susceptibility is inversely related to age in foals.

Transfusion With 2 L of Hyperimmune Plasma is Superior to Transfusion of 1 L or Less for Protecting Foals Against Subclinical Pneumonia Attributed to Rhodococcus equi.

Transfusing foals with Rhodococcus equi hyperimmune plasma (REHIP) is a standard practice at many horse-breeding farms to help prevent R. equi pneumonia. At many large breeding farms, pneumonia is most commonly recognized as subclinical based on thoracic ultrasonography findings.

In vitro evaluation of complement deposition and opsonophagocytic killing of Rhodococcus equi mediated by poly-N-acetyl glucosamine hyperimmune plasma compared to commercial plasma products.

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.