Prevalence Rates ofBorrelia burgdorferi(Spirochaetales: Spirochaetaceae),Anaplasma phagocytophilum(Rickettsiales: Anaplasmataceae), andBabesia microti(Piroplasmida: Babesiidae) in Host-SeekingIxodes scapularis(Acari: Ixodidae) from Pennsylvania

Abstract

The etiological agents responsible for Lyme disease (Borrelia burgdorferi), human granulocytic anaplasmosis (Anaplasma phagocytophilum), and babesiosis (Babesia microti) are primarily transmitted by the blacklegged tick, Ixodes scapularis Say. Despite Pennsylvania having in recent years reported the highest number of Lyme disease cases in the United States, relatively little is known regarding the geographic distribution of the vector and its pathogens in the state. Previous attempts at climate-based predictive modeling of I. scapularis occurrence have not coincided with the high human incidence rates in parts of the state. To elucidate the distribution and pathogen infection rates of I. scapularis, we collected and tested 1,855 adult ticks statewide from 2012 to 2014. The presence of I. scapularis and B. burgdorferi was confirmed from all 67 Pennsylvania counties. Analyses were performed on 1,363 ticks collected in the fall of 2013 to avoid temporal bias across years. Infection rates were highest for B. burgdorferi (47.4%), followed by Ba. microti (3.5%) and A. phagocytophilum (3.3%). Coinfections included B. burgdorferi+Ba. microti (2.0%), B. burgdorferi+A. phagocytophilum (1.5%) and one tick positive for A. phagocytophilum+Ba. microti. Infection rates for B. burgdorferi were lower in the western region of the state. Our findings substantiate that Lyme disease risk is high throughout Pennsylvania.

Adult Ixodes scapularis Ticks in a Lyme Disease Hot Spot are Vectors for Emerging Pathogens

“…We saw no evidence that coinfection occurred more or less often than expected based upon the co-infections predicted by combinations of the pathogens independent frequencies. Our coinfection rates for B. burgdorferi + A. phagocytophilum and B. microti+ A. phagocytophilum were similar to a prior study conducted in southwestern Pennsylvania [18]. In spite of these three pathogens potentially sharing some common animal reservoirs, we found B. burgdorferi to have an uneven distribution (independent of sample size) among the nine recreational areas we sampled which could be due to differences in prevalence of hosts these ticks feed on during the larvael or nymphal stages of their development [10].…”

“…Additionally, the number and/or source of blood meals, and thus the opportunity for infection, could possibly be the reason for marginal differences in B. burgdorferi (p = 0.054) and A. phagocytophilum (p = 0.078) prevalence between male and female ticks [10]. The 27% prevalence rate for B. microti in this study could be attributed to regional variation [20] and sampling of I. scapularis ticks for microbial pathogens in a high incidence southwestern Pennsylvania county compared to prior studies which sampled ticks from random locations in western Pennsylvania [18,19,21]. In support of our findings, a study by Piesman, et al [22] demonstrated the wide prevalence of B. microti (2%-47%) in adult I. scapularis from four areas in eastern Massachusetts.…”

“…The forward primer was 5' TTC AGG GTC TCA AGC GTC TTG GAC T 3' and the reverse primer were 5' GCA TTT TCA ATT TTA GCA AGT GAT G 3' amplifying a 276-bp product specific for the B. burgdorferi flagellin gene [18]. Amplification was performed as follows: 3 min at 98°C (one cycle) followed by 40 cycles for 5 sec at 98°C, 5 sec at 55°C, 30 sec at 72°C.…”

“…Chi-square tests also were used to test for the non-independence of multiple pathogens within ticks. Predicted frequencies of tick pathogen combinations were estimated by the combinations of their independent assortments [18,19].…”

County-Scale Distribution ofIxodes scapularisandIxodes pacificus(Acari: Ixodidae) in the Continental United States

“…No I. scapularis were collected during a statewide survey from 1963 to 1967 (Snetsinger 1968), whereas the tick was recorded from 49 of 67 counties by the late 1990s (Dennis et al 1998). A statewide survey conducted during 2012–2014 (Hutchinson et al 2015) revealed that the tick now is established in all 67 counties. It is likely that the east-to-west tick expansion across Pennsylvania continued into neighboring Ohio to the west, where active tick surveillance was conducted from 1983 to 2012.…”