Mary Killilea

Hosts as ecological traps for the vector of Lyme disease

Vectors of infectious diseases are generally thought to be regulated by abiotic conditions such as climate or the availability of specific hosts or habitats. In this study we tested whether blacklegged ticks, the vectors of Lyme disease, granulocytic anaplasmosis and babesiosis can be regulated by the species of vertebrate hosts on which they obligately feed. By subjecting field-caught hosts to parasitism by larval blacklegged ticks, we found that some host species (e.g. opossums, squirrels) that are abundantly parasitized in nature kill 83–96% of the ticks that attempt to attach and feed, while other species are more permissive of tick feeding. Given natural tick burdens we document on these hosts, we show that some hosts can kill thousands of ticks per hectare. These results indicate that the abundance of tick vectors can be regulated by the identity of the hosts upon which these vectors feed. By simulating the removal of hosts from intact communities using empirical models, we show that the loss of biodiversity may exacerbate disease risk by increasing both vector numbers and vector infection rates with a zoonotic pathogen.

The engaged university: providing a platform for research that transforms society

Despite a growing recognition that the solutions to current environmental problems will be developed through collaborations between scientists and stakeholders, substantial challenges stifle such cooperation and slow the transfer of knowledge. Challenges occur at several levels, including individual, disciplinary, and institutional. All of these have implications for scholars working at academic and research institutions. Fortunately, creative ideas and tested models exist that provide opportunities for conversation and serious consideration about how such institutions can facilitate the dialogue between scientists and society.

Spatial Dynamics of Lyme Disease: A Review

Lyme disease (LD), the most frequently reported vector-borne disease in the United States, requires that humans, infected vector ticks, and infected hosts all occur in close spatial proximity. Understanding the spatial dynamics of LD requires an understanding of the spatial determinants of each of these organisms. We review the literature on spatial patterns and environmental correlates of human cases of LD and the vector ticks, Ixodes scapularis in the northeastern and midwestern United States and Ixodes pacificus in the western United States. The results of this review highlight a need for a more standardized and comprehensive approach to studying the spatial dynamics of the LD system. Specifically, we found that the only environmental variable consistently associated with increased LD risk and incidence was the presence of forests. However, the reasons why some forests are associated with higher risk and incidence than others are still poorly understood. We suspect that the discordance among studies is due, in part, to the rapid developments in both conceptual and technological aspects of spatial ecology hastening the obsolescence of earlier approaches. Significant progress in identifying the determinants of spatial variation in LD risk and incidence requires that: (1) existing knowledge of the biology of the individual components of each LD system is utilized in the development of spatial models; (2) spatial data are collected over longer periods of time; (3) data collection and analysis among regions are more standardized; and (4) the effect of the same environmental variables is tested at multiple spatial scales.

Co-Infection of Blacklegged Ticks with Babesia microti and Borrelia burgdorferi Is Higher than Expected and Acquired from Small Mammal Hosts

Humans in the northeastern and midwestern United States are at increasing risk of acquiring tickborne diseases – not only Lyme disease, but also two emerging diseases, human granulocytic anaplasmosis and human babesiosis. Co-infection with two or more of these pathogens can increase the severity of health impacts. The risk of co-infection is intensified by the ecology of these three diseases because all three pathogens (Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti) are transmitted by the same vector, blacklegged ticks (Ixodes scapularis), and are carried by many of the same reservoir hosts. The risk of exposure to multiple pathogens from a single tick bite and the sources of co-infected ticks are not well understood. In this study, we quantify the risk of co-infection by measuring infection prevalence in 4,368 questing nymphs throughout an endemic region for all three diseases (Dutchess County, NY) to determine if co-infections occur at frequencies other than predicted by independent assortment of pathogens. Further, we identify sources of co-infection by quantifying rates of co-infection on 3,275 larval ticks fed on known hosts. We find significant deviations of levels of co-infection in questing nymphs, most notably 83% more co-infection with Babesia microti and Borrelia burgdorferi than predicted by chance alone. Further, this pattern of increased co-infection was observed in larval ticks that fed on small mammal hosts, but not on meso-mammal, sciurid, or avian hosts. Co-infections involving A. phagocytophilum were less common, and fewer co-infections of A. phagocytophilum and B. microti than predicted by chance were observed in both questing nymphs and larvae fed on small mammals. Medical practitioners should be aware of the elevated risk of B. microti/B. burgdorferi co-infection.

Reservoir Competence of Vertebrate Hosts for Anaplasma phagocytophilum

Fourteen vertebrate species (10 mammals and 4 birds) were assessed for their ability to transmit Anaplasma phagocytophilum, the bacterium that causes human granulocytic anaplasmosis, to uninfected feeding ixodid ticks. Small mammals were most likely to infect ticks but all species assessed were capable of transmitting the bacterium, in contrast to previous findings.

Overwintering Survival of Nymphal Ixodes scapularis (Acari: Ixodidae) Under Natural Conditions

ABSTRACT Blacklegged ticks (Ixodes scapularis Say) are exquisitely sensitive to very cold and dry conditions. For this reason it has long been assumed that climatic differences among locations and within microhabitats have a strong influence on variation in their survival over winter. This assumption, however, rests largely on laboratory exposures and on broad-scale associations between climatic variables and the observed distributions of ticks. We present the results of a study of the overwintering survival of I. scapularis nymphs in their natural environment from October through May in two locations in New York State using a repeated sampling strategy to determine when mortality occurred, and whether those events coincide with extreme conditions. We then fit these data to a simple, flexible statistical model in which the hazard of mortality varies with measurable conditions, here minimum daily temperature and mean daily relative humidity. Regardless of winter conditions, >80% of ticks survived at both sites. A model with constant hazard (i.e., independent of temperature and humidity) was best supported by the data. Although models with hazard increasing at temperatures below 0 deg C and at >90% relative humidity provided slightly better fits to the data, these models were less parsimonious. These results weaken the expectation that cold-related overwintering mortality necessarily plays a major role in restricting populations of these ticks and thus, risk of tick-borne zoonoses.

Molting success of Ixodes scapularis varies among individual blood meal hosts and species.

ABSTRACT The blacklegged tick (Ixodes scapularis) is an important vector of emerging human pathogens. It has three blood-feeding stages, as follows: larva, nymph, and adult. Owing to inefficient transovarial transmission, at least for the Lyme disease agent (Borrelia burgdorferi), larval ticks rarely hatch infected, but they can acquire infection during their larval blood meal. Nymphal ticks are primarily responsible for transmitting pathogens to hosts, including humans. The transition from uninfected host-seeking larva to infectious host-seeking nymph is therefore a key aspect of human risk of infection. It can be divided into a series of steps, as follows: finding a host, taking a blood meal, becoming infected, molting, and overwintering. The chance of succeeding in each of these steps may depend on the species identity of the blood meal host. We used a Bayesian method to estimate the molting success of larval I. scapularis collected from four commonly parasitized species of birds and eight commonly parasitized small and mid-sized mammals found in the forests of Dutchess County, New York. We show that molting success varies substantially among host species; white-footed mice, veeries, and gray catbirds support particularly high molting success, whereas ticks feeding on shorttailed shrews, robins, and wood thrushes were less successful. We also show that larval molting success varies substantially between individual blood meal hosts, and that this intraspecific variability is much higher in some species than in others. The causes of both inter- and intraspecific variation in molting success remain to be determined.

An Experimental Test of Competition among Mice, Chipmunks, and Squirrels in Deciduous Forest Fragments

Mixed hardwood forests of the northeast United States support a guild of granivorous/omnivorous rodents including gray squirrels (Sciurus carolinensis), eastern chipmunks (Tamias striatus), and white-footed mice (Peromyscus leucopus). These species coincide geographically, co-occur locally, and consume similar food resources. Despite their idiosyncratic responses to landscape and patch variables, patch occupancy models suggest that competition may influence their respective distributions and abundances, and accordingly their influence on the rest of the forest community. Experimental studies, however, are wanting. We present the result of a large-scale experiment in which we removed white-footed mice or gray squirrels from small, isolated forest fragments in Dutchess County, New York, and added these mammals to other fragments in order to alter the abundance of these two species. We then used mark–recapture analyses to quantify the population-level and individual-level effects on resident mice, squirrels, and chipmunks. Overall, we found little evidence of competition. There were essentially no within-season numerical responses to changes in the abundance of putative competitors. Moreover, while individual-level responses (apparent survival and capture probability) did vary with competitor densities in some models, these effects were often better explained by site-specific parameters and were restricted to few of the 19 sites we studied. With only weak or nonexistent competition among these three common rodent species, we expect their patterns of habitat occupancy and population dynamics to be largely independent of one another.

Prevalence of human-active and variant 1 strains of the tick-borne pathogen Anaplasma phagocytophilum in hosts and forests of eastern North America.

Anaplasmosis is an emerging infectious disease caused by infection with the bacterium Anaplasma phagocytophilum. In the eastern United States, A. phagocytophilum is transmitted to hosts through the bite of the blacklegged tick, Ixodes scapularis. We determined the realized reservoir competence of 14 species of common vertebrate hosts for ticks by establishing the probability that each species transmits two important strains of A. phagocytophilum (A. phagocytophilum human-active, which causes human cases, and A. phagocytophilum variant 1, which does not) to feeding larval ticks. We also sampled questing nymphal ticks from ∼ 150 sites in a single county over 2 years and sampled over 6 years at one location. White-footed mice (Peromyscus leucopus) and Eastern chipmunks (Tamias striatus) were the most competent reservoirs for infection with the A. phagocytophilum human-active strain. Across the county, prevalence in ticks for both strains together was 8.3%; ticks were more than two times as likely to be infected with A. phagocytophilum human-active as A. phagocytophilum variant 1.

Real-Time Social Data Collection in Rural Bangladesh via a ‘Microtasks for Micropayments’ Platform on Android Smartphones

The advent of cheap smartphones in rural areas across the globe presents an opportunity to change the mode with which researchers engage hard-to-reach populations. In particular, smartphones allow researchers to connect with respondents more frequently than standard household surveys, opening a new window into important short-term variability in key measures of household and community wellbeing. In this paper, we present early results from a pilot study in rural Bangladesh using a ‘microtasks for micropayments’ model to collect a range of community and household living standards data using Android smartphones. We find that more frequent task repetition with shorter recall periods leads to more inclusive reporting, improved capture of intra-seasonal variability, and earlier signals of events such as illness. Payments in the form of mobile talk time and data provide a positive development externality in the form of expanded access to mobile internet and social networks. Taken to scale, programs such as this have potential to transform data collection in rural areas, providing near-real-time windows into the development of markets, the spread of illnesses, or the diffusion of ideas and innovations.