Host associations of the tick, Ixodes angustus (Acari: Ixodidae), on Alaskan mammals

Establishing a baseline for tick surveillance in Alaska: Tick collection records from 1909-2019

The expanding geographic ranges of tick species that are known pathogen vectors can have implications for human, domestic animal, and wildlife health. Although Alaska is home to several hard tick species, it has historically been outside of the range of the most common medically important ticks in the contiguous United States and western Canada. To assess the status of tick species establishment in the state and to provide a baseline for tracking future change in the distribution of ticks, we reviewed and compiled historical tick records and summarized recent tick occurrence records collected through the development of the Alaska Submit-A-Tick Program and through tick drag sampling at sentinel sites in southcentral Alaska. Between 1909-2019, there were 1190 tick records representing 4588 individual ticks across 15 species in Alaska. The majority of ticks were species historically found in Alaska: Haemaphysalis leporispalustris, Ixodes angustus, Ixodes auritulus, Ixodes howelli, Ixodes signatus, and Ixodes uriae. Over half of all tick records in the state were collected in the last 10 yr. During this time, the number of tick records and the number of tick species recorded in Alaska each year has increased substantially. Between 2010-2019, there were 611 tick records representing 1921 individual ticks. The most common hosts for reported ticks were domestic animals (n = 343, 56 %) followed by small wild mammals (n = 147, 24 %), humans (n = 49, 8%), and wild birds (n = 31, 5%). Less than 5% of records (n = 25) were of unattached ticks found in the environment. Since 2007, non-native tick species have been documented in the state every year, including Amblyomma americanum, Dermacentor andersoni, Dermacentor occidentalis, Dermacentor variabilis, Ixodes pacificus, Ixodes ricinus, Ixodes scapularis, Ixodes texanus, and Rhipicephalus sanguineus sensu lato (s.l.). Almost half of the records (n = 68, 48 %) of non-native tick species from 2010 to 2019 represented ticks found on a host (usually a dog or a human) that had traveled outside of Alaska in the two weeks prior to collection. However, A. americanum, D. variabilis, I. pacificus, I. texanus, and R. sanguineus s.l. have been found on humans and domestic animals in Alaska without reported recent travel. In particular, there is evidence to suggest that there is local establishment of R. sanguineus s.l. in Alaska. A tick species historically found in the state, I. angustus was frequently found on human and dogs, suggesting a potential role as a bridge vector of pathogens. Given the inconsistency of tick monitoring in Alaska over the past century, it is difficult to draw many conclusions from temporal trends in the data. Continued monitoring through the Alaska Submit-A-Tick Program will allow a more accurate assessment of the changing risk of ticks and tick-borne diseases in the state and provide information for setting clinical and public health guidelines for tick-borne disease prevention.

Passive Animal Surveillance to Identify Ticks in Wisconsin, 2011-2017

The introduction of new tick species poses a risk to human and animal health. Systematic active surveillance programs are expensive and uncommon. We evaluated a passive animal surveillance program as a monitoring tool to document the geographic distribution and host associations of ticks in Wisconsin. Passive surveillance partners included veterinary medical clinics, domestic animal shelters, and wildlife rehabilitation centers from 35 of the 72 Wisconsin counties. A total of 10,136 tick specimens were collected from 2325 animals from July 2011 to November 2017 and included Dermacentor variabilis Say (29.7% of all ticks), Ixodes texanus Banks (25.5%), Ixodes scapularis Say (19.5%), Haemaphysalis leporispalustris Packard (13.8%), Ixodes cookei Packard (4.4%), and Dermacentor albipictus Packard (1.7%). Less common species (<1% of collection) included Ixodes dentatus Marx, Ixodes sculptus Neumann, Ixodes marxi Banks, Amblyomma americanum Linnaeus, and Rhipicephalus sanguineus Latreille. Of the 2325 animals that were examined, most were domestic dogs (53%), eastern cottontail rabbits (16%), domestic cats (15%), and North American raccoons (11%). An additional 21 mammal and 11 bird species were examined at least once during the six years of the study. New county records are summarized for each species. Public health, academic, and veterinary and animal care partners formed a community of practice enabling effective statewide tick surveillance.

Hyperparasitism and Non-Nidicolous Mating by Male Ixodes angustus Ticks (Acari: Ixodidae)

Ixodes angustus (Neumann) (Acari: Ixodidae) is considered to be a nidicolous tick in that the entire life cycle can be completed in the host nest. Males of this tick have been reported to be rare on hosts because most mating occurs in the host nest and males typically do not feed on hosts. Collections of I. angustus in Alaska departed slightly from this paradigm in that nine males were collected from hosts, mostly in copulation with females that were attached to mammalian hosts. Non-nidicolous mating was therefore more common in I. angustus collected in this study than has been reported previously. A hyperparasitic male I. angustus was found firmly attached via its hypostome and chelicerae to the ventral idiosoma of a partially engorged female I. angustus that was attached to, and feeding on, an American red squirrel, Tamiasciurus hudsonicus (Erxleben). This hyperparasitic interaction is discussed and illustrated with a Scanning Electron Micrograph.

New Records of Ticks (Acari: Ixodidae) From Dogs, Cats, Humans, and Some Wild Vertebrates in Alaska: Invasion Potential

During 2010-2016, tick specimens were solicited from veterinarians, biologists, and members of the public in Alaska. Eight species of ticks were recorded from domestic dogs. Some ticks were collected from dogs with recent travel histories to other countries or other U.S. states, which appears to explain records of ticks not native to Alaska such as Amblyomma americanum (L.) (lone star tick), Ixodes scapularis (Say) (blacklegged tick), and Ixodes ricinus (L.). However, we recorded Dermacentor variabilis (Say) (American dog tick) from dogs (and humans) both with and without travel history, suggesting that this nonindigenous tick could be establishing populations in Alaska. Other ticks commonly recorded from dogs included the indigenous Ixodes angustus Neumann and the invasive Rhipicephalus sanguineus (Latreille) (brown dog tick). Domestic cats were only parasitized by one tick species, the native I. angustus Six species of ticks were recorded from humans: A. americanum (with and without travel history), Dermacentor andersoni Stiles (Rocky Mountain wood tick; travel associated), D. variabilis (with and without travel history), Haemaphysalis leporispalustris (Packard) (rabbit tick, native to Alaska), I. angustus, and R. sanguineus. Ixodes angustus predominated among tick collections from native mammals. Also, Ixodes texanus Banks (first record from Alaska) was collected from an American marten, Martes americana (Turton), H. leporispalustris was recorded from a snowshoe hare, Lepus americanus Erxleben, and Ixodes auritulus Neumann was collected from a Northwestern crow, Corvus caurinus Baird. The establishment of D. variabilis, D. andersoni, A. americanum, and/or I. scapularis in Alaska would have strong implications for animal and human health.

Host, habitat and climate preferences of Ixodes angustus (Acari: Ixodidae) and infection with Borrelia burgdorferi and Anaplasma phagocytophilum in California, USA

The Holarctic tick Ixodes angustus is a competent vector for Borrelia burgdorferi, the etiologic agent of Lyme disease, and possibly Anaplasma phagocytophilum, the etiologic agent of granulocytic anaplasmosis, as well. From 2005 to 2013, we collected host-feeding I. angustus individuals from live-trapped small mammals and by flagging vegetation from 12 study sites in northern and central California, and tested for B. burgdorferi sensu lato, A. phagocytophilum, and Rickettsia spp. DNA by real-time PCR. Among 261 I. angustus collected (259 from hosts and two by flagging), the most common hosts were tree squirrels (20 % of ticks) and chipmunks (37 %). The PCR-prevalence for A. phagocytophilum and B. burgdorferi in ticks was 2 % and zero, respectively. The minimum infection prevalence on pooled DNA samples was 10 % for Rickettsia spp. DNA sequencing of the ompA gene identified this rickettsia as Candidatus Rickettsia angustus, a putative endosymbiont. A zero-inflated negative binomial mixed effects model was used to evaluate geographical and climatological predictors of I. angustus burden. When host species within study site and season within year were included in the model as nested random effects, all significant variables revealed that I. angustus burden increased as temperature decreased. Together with published data, these findings suggest that I. angustus is a host generalist, has a broad geographic distribution, is more abundant in areas with lower temperature within it's range, and is rarely infected with the pathogens A. phagocytophilum and B. burgdorferi.

Powassan virus in mammals, Alaska and New Mexico, U.S.A., and Russia, 2004-2007

Powassan virus is endemic to the United States, Canada, and the Russian Far East. We report serologic evidence of circulation of this virus in Alaska, New Mexico, and Siberia. These data support further studies of viral ecology in rapidly changing Arctic environments.

First report of Borrelia burgdorferi sensu lato in two threatened carnivores: the marbled polecat, Vormela peregusna and the European mink, Mustela lutreola (Mammalia: Mustelidae)

Background

Lyme disease is a widespread cosmopolitan zoonosis caused by species belonging to the genus Borrelia. It is transmitted from animal reservoir hosts to humans through hard - ticks of genus Ixodes which are vectors of the disease.

Case presentation

Borrelia burgdorferi sensu lato infection was identified in a marbled polecat, Vormela peregusna, and two European minks, Mustela lutreola, from Romania, by PCR. RFLP revealed the presence of a single genospecies, Borrelia burgdorferi sensu stricto.

Conclusions

This is the first report of the Lyme disease spirochetes in the two mentioned hosts.

Cold-stress response of engorged females of Rhipicephalus sanguineus

We investigated the effect of prolonged exposure to low temperature on engorged females of Rhipicephalus sanguineus. Five groups of two females (F1-F5) were maintained at 8 ± 2°C, 70 ± 10% RH, and 24 h scotophase, for 15, 30, 45, 60 and 75 days. One group was maintained in the incubator (26 ± 1°C, 70 ± 10% RH, and 24 h scotophase) as control. The results show that egg hatch rate, longevity and reproductive fitness of engorged females of R. sanguineus are negatively correlated with the duration of exposure to low temperature, whereas preoviposition period was positively correlated with exposure to the cold. This shows that the engorged female ticks are sensitive to prolonged exposure to low temperature, and it may explain why females of this tick species are not reproductively active during winter. Our results confirm that temperature is a major limiting factor for the establishment of stable R. sanguineus populations in cold temperate regions of Europe.

Nestedness of ectoparasite-vertebrate host networks

Determining the structure of ectoparasite-host networks will enable disease ecologists to better understand and predict the spread of vector-borne diseases. If these networks have consistent properties, then studying the structure of well-understood networks could lead to extrapolation of these properties to others, including those that support emerging pathogens. Borrowing a quantitative measure of network structure from studies of mutualistic relationships between plants and their pollinators, we analyzed 29 ectoparasite-vertebrate host networks—including three derived from molecular bloodmeal analysis of mosquito feeding patterns—using measures of nestedness to identify non-random interactions among species. We found significant nestedness in ectoparasite-vertebrate host lists for habitats ranging from tropical rainforests to polar environments. These networks showed non-random patterns of nesting, and did not differ significantly from published estimates of nestedness from mutualistic networks. Mutualistic and antagonistic networks appear to be organized similarly, with generalized ectoparasites interacting with hosts that attract many ectoparasites and more specialized ectoparasites usually interacting with these same “generalized” hosts. This finding has implications for understanding the network dynamics of vector-born pathogens. We suggest that nestedness (rather than random ectoparasite-host associations) can allow rapid transfer of pathogens throughout a network, and expand upon such concepts as the dilution effect, bridge vectors, and host switching in the context of nested ectoparasite-vertebrate host networks.

Significant morphological but little molecular differences between Trypanosoma of rodents from Alaska

We examined blood smears of 173 rodents and 33 shrews captured at 4 sites in the Gates of the Arctic National Park, northern Alaska, in summer 2002. Trypanosoma spp. were detected in the plasma of 5 Microtus oeconomus, 4 Microtus miurus, and 1 Lemmus trimucronatus. The trypomastigote morphology from different individuals of M. oeconomus caught at the same site and of M. miurus from different sites varied significantly. The 4 DNA sequences obtained from the blood smear positive samples contained 2 different haplotypes very similar to each other and to that of Trypanosoma microti. Of possible vectors of blood parasites, the flea Amalaraeus dissimilis was collected from M. miurus.