Avian Reservoirs of the Agent of Human Granulocytic Ehrlichiosis?

To the Editor: Human granulo-cytic ehrlichiosis (HGE), first described in 1994 (1), is the second-most common tick-borne disease in the United States; Lyme disease is the most prevalent. Both diseases are transmitted by blacklegged ticks (Ixodes scapularis Say) that are abundant in southern New York state (2). Factors that influence the risk for infection, particularly the role of wildlife in transmitting the etio-logic agent, Anaplasma (formerly Ehr-lichia) phagocytophilum (3,4), to vector ticks are not well understood. In the absence of transovarial transmission (5,6), acquisition of A. phagocyto-philum by its vector must result either from feeding on the blood of reservoir-competent hosts or by cofeeding of uninfected ticks in close proximity to infected ticks (7). The role that birds may play in HGE ecology is potentially very important. Birds in the northeastern United States routinely host immature I. scapularis (8), and several species are competent reservoirs of Borrelia burgdorferi (9), the causative agent of Lyme disease, thus providing an opportunity to transport infected ticks to new areas. While data for HGE are lacking, A. phagocytophilum–infected I. ricinus nymphs have been collected from migrating birds in Sweden (10); reservoir competence was not established , however. Our goal was to determine if several common bird species might serve as reservoirs of A. phagocytophilum and, as such, transmit the pathogen to feeding I. scapu-laris larvae. Birds were sampled at a deciduous woodland preserve in Tarrytown, Westchester County, New York, an area where Lyme disease and HGE are endemic. Birds were captured with Japanese mist nets (#3, EBBA Net Committee, Bryn Athyn, PA), and all captures were examined for ectopara-sites. Ticks were removed with for-ceps and preserved in 70% ethanol for later identification and testing. Birds were then banded and released unharmed. Host-seeking larvae also were collected by drag sampling at the site to further evaluate the potential for transovarial transmission of the HGE agent. To ensure that all larvae were not from a single egg mass, no more than 25 specimens were collected from a single drag. A total of 123 larval I. scapularis were collected from birds captured in May 1993 (one American robin [Tur-dus migratorius] hosting two larvae), July 1997 (one American robin host-ing 31 larvae), and August 1997 (two veerys [Catharus fuscescens] hosting 10 and 42 larvae, respectively; one wood thrush [Hylocichla mustelina] hosting 19 larvae; and one rose-breasted grosbeak [Pheucticus ludovi-cianus] hosting 19 larvae). Additionally , 10 I. scapularis nymphs …