Laboratory Blood-Based Testing for Non-Lyme Disease Tick-Borne Infections at a National Reference Laboratory

Sex- and Age-Specific Lyme Disease Testing Patterns in the United States, 2019 and 2022

OBJECTIVES

Serologic testing is a useful adjunct for the diagnosis of Lyme disease, a major public health problem in certain US regions. We aimed to determine whether Lyme disease serologic testing and results differed by sex and age group.

METHODS

We identified 2 cohorts of individuals across all ages who underwent serologic testing for Lyme disease at a national reference laboratory in 2019 (cohort 1) and 2022 (cohort 2). If an individual had multiple tests in the same year, we included only the first test. We excluded individuals who had been tested in the previous 5 years.

RESULTS

Cohorts 1 and 2 consisted of 578 052 and 550 674 people, respectively. Fewer males than females were tested in cohort 1 (42.7% vs 57.3%) and cohort 2 (42.3% vs 57.7%), although similar numbers were tested for both sexes among nonadults. More males than females had a positive test result in cohort 1 (53.9% more males) and cohort 2 (52.9% more males). The odds ratio of receiving a positive test result among males versus females was 2.09 (95% CI, 2.01-2.17) in cohort 1 and 2.12 (95% CI, 2.05-2.19) in cohort 2. Among people with positive test results, females (except children) were more likely than males to have positive immunoglobulin M and negative immunoglobulin G results, which can serve as a marker of early infection (odds ratio = 1.43 [95% CI, 1.31-1.55] in cohort 1 and 1.38 [95% CI, 1.29-1.47] in cohort 2).

CONCLUSIONS

Further studies are needed to understand whether the observed differences in Lyme disease testing and positivity result from sex- and age-associated disparities in social behavior, health care seeking, clinical practice, or other factors.

Ticks and Tick-Borne Pathogens in Domestic Animals, Wild Pigs, and Off-Host Environmental Sampling in Guam, USA

Background: Guam, a United States of America (USA) island territory in the Pacific Ocean, is known to have large populations of ticks; however, it is unclear what the risk is to wildlife and humans living on the island. Dog (Canis familiaris), cat (Felis catus), and wild pig (Sus scrofa) sentinels were examined for ticks, and environmental sampling was conducted to determine the ticks present in Guam and the prevalence of tick-borne pathogens in hosts.

Methods and Results: From March 2019-November 2020, ticks were collected from environmental sampling, dogs, cats, and wild pigs. Blood samples were also taken from a subset of animals. A total of 99 ticks were collected from 27 environmental samples and all were Rhipicephalus sanguineus, the brown dog tick. Most ticks were collected during the dry season with an overall sampling success rate of 63% (95% CI: 42.4–80.6). 6,614 dogs were examined, and 12.6% (95% CI: 11.8–13.4) were infested with at least one tick. One thousand one hundred twelve cats were examined, and six (0.54%; 95% CI: 0.20–1.1) were found with ticks. Sixty-four wild pigs were examined and 17.2% (95% CI: 9.5–27.8) had ticks. In total, 1,956 ticks were collected and 97.4% of ticks were R. sanguineus. A subset of R. sanguineus were determined to be the tropical lineage. The other tick species found were Rhipicephalus microplus (0.77%), Amblyomma breviscutatum (0.77 %), and a Haemaphysalis sp. (0.51%). Blood samples from 136 dogs, four cats, and 64 wild pigs were tested using polymerase chain reaction (PCR) and DNA sequencing methods. Five different tick-borne pathogens with the following prevalences were found in dogs: Anaplasma phagocytophilum 5.9% (95% CI: 2.6–11.3); Anaplasma platys 19.1% (95% CI: 12.9–26.7); Babesia canis vogeli 8.8% (95% CI: 4.6–14.9); Ehrlichia canis 12.5% (95% CI: 7.5–19.3); Hepatozoon canis 14.7% (95% CI: 9.2–28.8). E. canis was detected in one cat, and no tick-borne pathogens were detected in wild pigs. Overall, 43.4% (95% CI: 34.9–52.1) of dogs had at least one tick-borne pathogen. Serological testing for antibodies against Ehrlichia spp. and Anaplasma spp. showed prevalences of 14.7% (95% CI: 9.2–28.8) and 31.6% (95% CI: 23.9–40), respectively.

Conclusion: Four different tick species were found in Guam to include a Haemaphysalis sp., which is a previously unreported genus for Guam. Dogs with ticks have a high prevalence of tick-borne pathogens which makes them useful sentinels.

Targeted Metagenomics for Clinical Detection and Discovery of Bacterial Tick-Borne Pathogens

Tick-borne diseases, due to a diversity of bacterial pathogens, represent a significant and increasing public health threat throughout the Northern Hemisphere. A high-throughput 16S V1-V2 rRNA gene-based metagenomics assay was developed and evaluated using >13,000 residual samples from patients suspected of having tick-borne illness and >1,000 controls. Taxonomic predictions for tick-borne bacteria were exceptionally accurate, as independently validated by secondary testing. Overall, 881 specimens were positive for bacterial tick-borne agents. Twelve tick-borne bacterial species were detected, including two novel pathogens, representing a 100% increase in the number of tick-borne bacteria identified compared to what was possible by initial PCR testing. In three blood specimens, two tick-borne bacteria were simultaneously detected. Seven bacteria, not known to be tick transmitted, were also confirmed to be unique to samples from persons suspected of having tick-borne illness. These results indicate that 16S V1-V2 metagenomics can greatly simplify diagnosis and accelerate the discovery of bacterial tick-borne pathogens.