title: Antibody index and specific antibody quotient in horses after intragastric administration of Sarcocystis neurona sporocysts.
abstract: OBJECTIVE
  To investigate the use of a specific antibody index (AI) that relates Sarcocystis neurona-specific IgG quotient (Q(SN)) to total IgG quotient (Q(IgG)) for the detection of the anti-S neurona antibody fraction of CNS origin in CSF samples obtained from horses after intragastric administration of S neurona sporocysts.
  
  
  METHODS
  18 adult horses.
  
  
  METHODS
  14 horses underwent intragastric inoculation (day 0) with S neurona sporocysts, and 4 horses remained unchallenged; blood and CSF samples were collected on days - 1 and 84. For purposes of another study, some challenged horses received intermittent administration of ponazuril (20 mg/kg, PO). Sarcocystis neurona-specific IgG concentrations in CSF (SN(CSF)) and plasma (SN(plasma)) were measured via a direct ELISA involving merozoite lysate antigen and reported as ELISA units (EUs; arbitrary units based on a nominal titer for undiluted immune plasma of 100,000 EUs/mL). Total IgG concentrations in CSF (IgG(CSF)) and plasma (IgG(plasma)) were quantified via a sandwich ELISA and a radial immunodiffusion assay, respectively; Q(SN), Q(IgG), and AI were calculated.
  
  
  RESULTS
  Following sporocyst challenge, mean +/- SEM SN(CSF) and SN(plasma) increased significantly (from 8.8 +/- 1.0 EUs/mL to 270.0 +/- 112.7 EUs/mL and from 1,737 +/- 245 EUs/mL to 43,169 +/- 13,770 EUs/mL, respectively). Challenge did not affect total IgG concentration, Q(SN), Q(IgG), or AI.
  
  
  CONCLUSIONS
  S neurona-specific IgG detected in CSF samples from sporocyst-challenged horses appeared to be extraneural in origin; thus, this experimental challenge may not reliably result in CNS infection. Calculation of a specific AI may have application to the diagnosis of S neurona-associated myeloencephalitis in horses.
authors.affiliation: Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Heskett
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Mackay
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000276:immunology*; D000918:Antibody Specificity; D004679:Encephalomyelitis / Q000134:cerebrospinal fluid / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D006734:Horse Diseases / Q000175:diagnosis / Q000276:immunology* / Q000469:parasitology*; D006736:Horses; D005779:Immunodiffusion / Q000662:veterinary; D007074:Immunoglobulin G / Q000134:cerebrospinal fluid; D012522:Sarcocystis / Q000276:immunology / Q000302:isolation & purification*; D012523:Sarcocystosis / Q000134:cerebrospinal fluid / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*
chemical_list: D000913:Antibodies, Protozoan; D007074:Immunoglobulin G