Risk factors of Bartonella spp. infection and the association between Bartonella spp. and T-lymphocyte subset alteration in asymptomatic retrovirus-infected cats in Bangkok Metropolitan, Thailand

Abstract

Background and aim: Cats are a reservoir for Bartonella spp. infection in humans. Human bartonellosis causes disseminated inflammation to develop in immunocompromised patients, such as those infected with human immunodeficiency virus. However, the associated risks of Bartonella spp. infection in immunocompromised retroviral-infected cats have been inconclusive. This study aimed to evaluate the associated risks of Bartonella spp. infection with the alteration of T-lymphocyte subsets of retroviral-infected cats.

Materials and methods: We collected blood samples from 161 client-owned cats at veterinary clinics and hospitals throughout the Bangkok Metropolitan area from 2017 to 2020. The samples underwent hematological biochemical tests, feline retroviral status evaluation, Bartonella spp. polymerase chain reaction assay, immunofluorescence assay, and CD4⁺ and CD8⁺ lymphocyte counts. Risk factors associated with Bartonella spp. infection were determined by odds ratio (OR). Hematological and biochemical parameters were compared using independent t-tests. CD4⁺ and CD8⁺ lymphocyte counts and the CD4⁺/CD8⁺ ratio were compared among groups classified according to their retroviral and Bartonella spp. infection status.

Results: The prevalence of Bartonella spp. in our study cohort was 16.1%, and the seroprevalence was 94.9%. Cats aged >1 year were at a higher risk of seropositivity than cats aged <1 year (OR: 4.296, 95% confidence interval: 1.010-18.275). The CD8⁺ percentage was significantly higher in seropositive cats (p = 0.026). There was a significant reduction in the CD4⁺/CD8⁺ ratio between cats negative for both retrovirus and Bartonella spp. infection and cats with concurrent retrovirus and Bartonella spp. infection (p = 0.041).

Conclusion: In endemic countries or areas, cat owners must be made aware of the risk of exposure to Bartonella spp. due to the high rate of bacteremia and seroprevalence. Retrovirus-infected cats with concurrent Bartonella spp. infection also showed a significant, inverted CD4⁺/CD8⁺ ratio, which may be used as a novel marker in bartonellosis. Similar studies focusing on the different stages of retrovirus infection should be undertaken further to elucidate the effect of retrovirus infection on Bartonella spp. infection.

Keywords: Bartonella spp; T-lymphocyte subsets; cats; feline immunodeficiency virus; feline leukemia virus; retrovirus; risk factors.

Figure-1

Identification of Bartonella spp. by a nested polymerase chain reaction in 16S-23S rDNA intergenic regions. M lane is DNA ladder. P lane is positive control showed expected band at 152 bp fragment for Bartonella henselae (arrow). N lane is negative control. Lanes 2 and 5 showed positivity.

Figure-2

Representative flow cytometry analysis of CD4⁺ and CD8⁺ lymphocytes. (a) Forward scatter height (FS, X-axis) was plotted against side scatter height (SS, Y-axis) to select a lymphocyte population. (b) CD8⁺ PE (CD8⁺, X-axis) was plotted against CD4⁺ FIT-C (CD4⁺, Y-axis). (c and d) are histograms of CD4⁺ and CD8⁺ T-lymphocytes, respectively.

Figure-3

Column scatter plot of CD4⁺ to CD8⁺ ratios in four groups of cats with different retrovirus and Bartonella spp. statuses. Gr.1: Healthy cats who tested negative for both Bartonella spp. Polymerase chain reaction (PCR) and retrovirus; Gr.2: Cats who tested negative for Bartonella spp. PCR but positive for retrovirus; Gr.3: Cats who tested positive for Bartonella spp. PCR but negative for retrovirus; and Gr.4: Cats who tested positive for both Bartonella spp. PCR and retrovirus.