Antibody responses to Sarcoptes scabiei apolipoprotein in a porcine model: relevance to immunodiagnosis of recent infection

Abstract

No commercial immunodiagnostic tests for human scabies are currently available, and existing animal tests are not sufficiently sensitive. The recombinant Sarcoptes scabiei apolipoprotein antigen Sar s 14.3 is a promising immunodiagnostic, eliciting high levels of IgE and IgG in infected people. Limited data are available regarding the temporal development of antibodies to Sar s 14.3, an issue of relevance in terms of immunodiagnosis. We utilised a porcine model to prospectively compare specific antibody responses to a primary infestation by ELISA, to Sar s 14.3 and to S. scabiei whole mite antigen extract (WMA). Differences in the antibody profile between antigens were apparent, with Sar s 14.3 responses detected earlier, and declining significantly after peak infestation compared to WMA. Both antigens resulted in >90% diagnostic sensitivity from weeks 8-16 post infestation. These data provide important information on the temporal development of humoral immune responses in scabies and further supports the development of recombinant antigen based immunodiagnostic tests for recent scabies infestations.

Figure 1. IgG reactivity of S. scabiei whole mite antigen extract (WMA) and Sar s 14.3 with porcine sera.

A: 4–20% coomassie stained SDS-PAGE gel loaded with lane 1: prestained molecular weight marker, lane 2: WMA, 5 µg, lane 3: Sar s 14.3 (2 µg). Corresponding Western Blots probed with sera from mange infected pigs (B) and non-infected pigs (C).

Figure 2. Lesion development in mange infected pigs.

Ear lesions were scored weekly. Score of 1–4: acute mange with generalised rash and papular lesions of increasing density, >4: development of increasing encrustment, 8: extensive encrustment spreading external to ears. A: Comparison of treatment groups (n = 6 per group), error bars represent mean ±SEM. B: Clinical variation in mange severity in individual pigs from the non-Dex treatment group.

Figure 3. Isotype specific WMA (1) and Sar s 14.3 (2) antibody responses over 24 weeks for the four pig treatment groups.

Error bars represent mean ±SEM. *: p<0.05, compared to group D (Dex −/Mange -) (two way repeated measures ANOVA). The first two weeks were not tested by ANOVA due to the requirement for matched numbers, and insufficient sera samples from some pigs.

Figure 4. Correlation between lesion severity and antibody response.

Scatter plot showing lesion score and ELISA units from mange infected pigs in the non-Dex treatment group from weeks 8–20 post infection. Each point represents the lesion score and antibody level for an individual pig at a single time point. R: Spearmans correlation coefficient.