Interlaboratory Optimization and Evaluation of a Serological Assay for Diagnosis of Human Baylisascariasis

Abstract

A Western blot assay using a recombinant protein, recombinant Baylisascaris procyonis RAG1 protein (rBpRAG1), was developed for the diagnosis of human baylisascariasis concurrently by the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, and the National Reference Centre for Parasitology (NRCP) in Montreal, Canada. Assay performance was assessed by testing 275 specimens at the CDC and 405 specimens at the NRCP. Twenty specimens from 16 cases of baylisascariasis were evaluated. Eighteen were positive, with the assay correctly identifying 14 of 16 patients. The rBpRAG1 Western blot assay showed no cross-reactivity with Toxocara-positive serum and had an overall sensitivity of 88% and a specificity of 98%.

Update on Baylisascariasis, a Highly Pathogenic Zoonotic Infection

“…Moreover, no (0/66) cross-reactivity with Toxocarapositive serum samples was observed, although some (8/280) reactivity was detected with the sera obtained from noninfected patients and with sera from patients with strongyloidiasis (1/8), malaria (3/10), and filariasis (1/7). However, it was pointed out that if the full infection history of these test sera was not known, e.g., if possible cross-reactors might also be infected with Baylisascaris as covert dual infections, the actual levels of sensitivity and specificity of the assay might even be higher than reported (121). This Western blot assay employing rBpRAG1 is currently considered the "gold standard" for serodiagnosis of baylisascariasis and is being performed by the CDC and the NRCP-CA (121).…”

“…Both ELISA and immunoblotting methods are quite sensitive, since patients with clinical CNS disease usually have strongly positive immunological results from both serum and CSF samples (119,120,121) (Table 2). Brain biopsies or analyses of autopsy material have also confirmed a diagnosis of baylisascariasis in several of these patients (34,35,36,41).…”

“…The estimated sensitivity and specificity of the rBpRAG1 ELISA were 85% and 86.9%, respectively, compared to only 39.4% specificity for the B. procyonis ES-Ag ELISA (120), but cross-reactivity was still detected in 25% of the samples containing Toxocara-positive serum (120). The rBpRAG1 antigen was donated to the Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA, and the National Reference Centre for Parasitology, Canada (NRCP-CA), whose researchers worked jointly to develop a Western blotting assay for the diagnosis of human baylisascariasis (121). In Western blot assays of 680 samples, detection by rBpRAG1 had an overall sensitivity of 88% and a specificity of 98% (121).…”

“…The rBpRAG1 antigen was donated to the Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA, and the National Reference Centre for Parasitology, Canada (NRCP-CA), whose researchers worked jointly to develop a Western blotting assay for the diagnosis of human baylisascariasis (121). In Western blot assays of 680 samples, detection by rBpRAG1 had an overall sensitivity of 88% and a specificity of 98% (121). Moreover, no (0/66) cross-reactivity with Toxocarapositive serum samples was observed, although some (8/280) reactivity was detected with the sera obtained from noninfected patients and with sera from patients with strongyloidiasis (1/8), malaria (3/10), and filariasis (1/7).…”

Clinical Reasoning: A 15-month-old boy with progressive lethargy and spasticity

“…Diagnosis is confirmed if there is a positive immunoglobulin G (IgG), as determined by a Western blot assay using antigen rBpRAG1, from the serum or CSF. 3 In this patient, testing done by the CDC revealed a positive serum IgG but a negative CSF IgG. Although both serum and CSF antibodies are often positive, there have been multiple similar cases reported where only the serum tested positive.…”