Clinical canine Borrelia burgdorferi (sensu lato) infections are associated with highly elevated total IgG ELISA titers and convalescent Th2 immune responses

Abstract

Lyme disease is caused by Borrelia burgdorferi (sensu lato), which is transmitted through species belonging to the Ixodes ricinus complex. Canine Lyme Disease (CLD) is an established clinical entity in the USA. In Europe, an unambiguous diagnosis is rarely made, although it has been shown that dogs can be naturally infected and develop antibodies against B. burgdorferi (s.l.). The relation of Borrelia total IgG, IgG2, and IgG1 specific antibodies and the incidence of symptoms was studied in a prospective cohort study. In a tick-dense area in the Netherlands, 84 dogs in 4 age cohorts were followed up during 7 consecutive half-years. In addition, 31 Bernese Mountain dogs (BMD), known to have robust anti-Borrelia antibody responses, were clinically monitored and serologically examined. Generalized estimating equations (GEE) analysis on repeated half-year measurements of clinical and serological results showed a strong association between the clinical signs fever combined with lameness in time, which in turn was associated with transiently high total IgG titers and elevated IgG1 titers against B. burgdorferi (sensu stricto). In BMD, we observed seroconversions and persistence of specific high total IgG and IgG1 titers. Although the latter also developed a persistent reaction against the B. burgdorferi (s.l.) C6 peptide, their tissues tested negative for B. burgdorferi (s.l.) DNA. This study strongly suggests that dogs - not vaccinated against Borrelia spp. infections - that encounter yearly tick infestations are recurrently infected. Some breeds, such as Labrador Retrievers and BMD, in the course of multiple tick-infestation seasons, develop transient symptoms compatible with CLD. Symptoms were strongly associated with temporarily raised total IgG and concomitant or convalescent high IgG1 antibody responses against B. burgdorferi (sensu stricto). Our findings provide insights into the resistance of dogs against B. burgdorferi (s.l.) infections and show that transient symptoms of CLD only occur in a subset of infected dogs.

Keywords: Borrelia; Canine lyme disease (CLD); Diagnosis; Dog; IgG whole cell ELISA; IgG1; Seasons; Seroconversion; Ticks.

Graphical abstract

Fig. 1

Monthly distribution of ticks on the vegetation and on dogs in the year 1993, as a percentage of the total yearly catch of adult ticks in one year. The distribution of nymphal ticks on the vegetation throughout the year was bimodal, with a second peak in September (not shown). Most ticks found on the skin of dogs were adult female ticks.

Fig. 2

Mean total IgG whole cell ELISA titers with standard error of the mean (SEM) per quarter year in the first 6 tick-seasons with 355 samples of 56 dogs (cohort 1, 2 and part of cohort 3). Each point is a quarter-year in sequence starting with Q1 - winter - of first tick-season (mean titer 2.0).

Fig. 3

A Frequency distribution of total IgG and IgG2 whole cell ELISA titer results with a normal distribution and IgG1 ELISA results with a lognormal distribution (Kolmogorov-Smirnov test). The 0 result is in fact a titer < 1; total n of all titer data is 328. B IgG2 and IgG1 results compared to total IgG categories 1 to 4 (1–4), 5 and 6 (5–6), and 7 and 9 (7–9). Note: “9” as a titer signifies that the last dilution step in the ELISA plate, titer 8 (dilution 1/2560) is as dark or darker in coloration.

Fig. 4

Mean IgG1 whole cell ELISA titers (bars) with standard error of the mean (SEM). For the cohort dogs during 12 low-risk (LR) and high-risk (HR) tick-seasons, not included the 4 BMD. Presented as tick-seasons 1–12 (cohorts 1–4, n = 80 dogs) and tick-seasons 1–6 (cohorts 1–3, n = 54 dogs). The last tick-season number 12 is a combination of samples from the older dogs that had experienced more than 12 tick-seasons in 1994 for which tick-seasons were grouped together as the 12th season. The tick-seasons are split for high-risk (Q2 and Q3) and low-risk (Q4, and Q1 of the following year) for tick infestations. All data are measured, imputed data are not presented in this graph. The individual data are displayed with the appropriate bar of the mean IgG1 ELISA titers. The range of exceptionally high values at low-risk tick-seasons (light blue colored dots) appears wider than at high-risk seasons (red colored dots) resulting in higher means for LR with larger standard deviations, and SEM at the first 6 tick-seasons. The first LR tick-season is shown in the graph but not incorporated in the statistics (mixed-effect model, Table 6).