First record of a structural infestation by the bird flea Dasypsyllus gallinulae perpinnatus (Siphonaptera: Ceratophyllidae) in the San Francisco Bay Area, California, USA.

Herein we present the first-known case report of a structural infestation by the bird flea (Dasypsyllus gallinulae perpinnatus) (Dale 1878) in the United States. In March of 2023, the San Mateo County Mosquito and Vector Control District was contacted by a resident in South San Francisco, CA who reported the presence of fleas inside their condominium. The resident had 2 dogs who were on oral flea medication and only 1 inhabitant out of 4 reported receiving flea bites. The front walkway, backyard, and garage were flagged and a small passerine nest was removed from a fire alarm bell in the front walkway. A total of 31 fleas (13 males, 18 females) were collected by flagging from the front entryway underneath the nest. One female flea was collected from the backyard, and 20 (9 males, 11 females) were collected by the resident from inside the house. A total of 387 fleas (163 males, 224 females) were collected from the nest of a small passerine. All life stages (egg, larvae, pupae, and adult) were observed within the nest. Additional parasites in the nest included bird lice and larval western black-legged ticks (Ixodes pacificus, Cooley and Kohls 1943). Research should be conducted into whether bird fleas are capable of transmitting avian pathogens to humans and this information should be communicated to healthcare providers as part of a One Health approach. Additionally, resources to aid in species-level flea identification should be made accessible to pest control operators as this will aid the development of targeted treatments as part of an integrated pest management plan.

Macro-parasites and micro-parasites co-exist in rodent communities but are associated with different community-level parameters.

Wildlife species are often heavily parasitized by multiple infections simultaneously. Yet research on sylvatic transmission cycles, tend to focus on host interactions with a single parasite and neglects the influence of co-infections by other pathogens and parasites. Co-infections between macro-parasites and micro-parasites can alter mechanisms that regulate pathogenesis and are important for understanding disease emergence and dynamics. Wildlife rodent hosts in the Lyme disease system are infected with macro-parasites (i.e., ticks and helminths) and micro-parasites (i.e., Borrelia spp.), however, there has not been a study that investigates the interaction of all three parasites (i.e., I. pacificus, Borrelia spp., and helminths) and how these co-infections impact prevalence of micro-parasites. We live-trapped rodents in ten sites in northern California to collect feces, blood, ear tissue, and attached ticks. These samples were used to test for infection status of Borrelia species (i.e., micro-parasite), and describe the burden of ticks and helminths (i.e., macro-parasites). We found that some rodent hosts were co-infected with all three parasites, however, the burden or presence of concurrent macro-parasites were not associated with Borrelia infections. For macro-parasites, we found that tick burdens were positively associated with rodent Shannon diversity while negatively associated with predator diversity, whereas helminth burdens were not significantly associated with any host community metric. Ticks and tick-borne pathogens are associated with rodent host diversity, predator diversity, and abiotic factors. However, it is still unknown what factors helminths are associated with on the community level. Understanding the mechanisms that influence co-infections of multiple types of parasites within and across hosts is an increasingly critical component of characterizing zoonotic disease transmission and maintenance.

Five Years of Surveillance for Tularemia Serovar B (Francisella tularensis holarctica) (Olsufjev) (Thiotrichales: Francisellaceae) Including Two Human Cases at an Endemic Site in San Mateo County, California.

Tularemia is a highly infectious, potentially fatal disease of humans and animals caused by the gram negative, intracellular bacterium Francisella tularensis. The San Mateo County Mosquito and Vector Control District conducted surveillance for F. tularensis from 2017 to 2021 in Dermacentor occidentalis (Marx) (Ixodida: Ixodidae), D. variabilis (Say) (Ixodida: Ixodidae), and Haemaphysalis leporispalustris (Packard) (Ixodida: Ixodidae) ticks in coastal southwestern San Mateo County, California. A total of 3,021 D. occidentalis and 1,019 D. variabilis were collected. Of those, 25 positive pools of F. tularensis were detected (five ticks per pool, overall minimum infection prevalence: 0.62%). Twenty-two of the 25 positive pools (88%) contained D. occidentalis. Eighty-eight percent (88%) of all positive pools were collected from the western half of the site, nearest to the ocean. We did not detect a seasonal effect on the probability of detecting a positive tick pool. There were two human cases of tularemia during the summers of 2019 and 2021. We conducted rodent surveillance in June of 2019, before the human case report. Twenty-four small mammals were collected, but none of their sera tested positive for F. tularensis. It is clear that tularemia is endemic to this region of San Mateo County, but the extent of its range and its ecology is not currently well understood.

Local Community Composition Drives Avian Borrelia burgdorferi Infection and Tick Infestation.

Globally, zoonotic vector-borne diseases are on the rise and understanding their complex transmission cycles is pertinent to mitigating disease risk. In North America, Lyme disease is the most commonly reported vector-borne disease and is caused by transmission of Borrelia burgdorferi sensu lato (s.l.) from Ixodes spp. ticks to a diverse group of vertebrate hosts. Small mammal reservoir hosts are primarily responsible for maintenance of B. burgdorferi s.l. across the United States. Nevertheless, birds can also be parasitized by ticks and are capable of infection with B. burgdorferi s.l. but their role in B. burgdorferi s.l. transmission dynamics is understudied. Birds could be important in both the maintenance and spread of B. burgdorferi s.l. and ticks because of their high mobility and shared habitat with important mammalian reservoir hosts. This study aims to better understand the role of avian hosts in tick-borne zoonotic disease transmission cycles in the western United States. We surveyed birds, mammals, and ticks at nine sites in northern California for B. burgdorferi s.l. infection and collected data on other metrics of host community composition such as abundance and diversity of birds, small mammals, lizards, predators, and ticks. We found 22.8% of birds infected with B. burgdorferi s.l. and that the likelihood of avian B. burgdorferi s.l. infection was significantly associated with local host community composition and pathogen prevalence in California. Additionally, we found an average tick burden of 0.22 ticks per bird across all species. Predator and lizard abundances were significant predictors of avian tick infestation. These results indicate that birds are relevant hosts in the local B. burgdorferi s.l. transmission cycle in the western United States and quantifying their role in the spread and maintenance of Lyme disease requires further research.

Host infection and community composition predict vector burden.

Lyme disease is the most prevalent vector-borne disease in the United States, yet critical gaps remain in our understanding of tick and host interactions that shape disease dynamics. Rodents such as deer mice (Peromyscus spp.) and dusky-footed woodrats (Neotoma fuscipes) are key reservoirs for Borrelia burgdorferi, the etiological bacterium of Lyme disease, and can vary greatly in abundance between habitats. The aggregation of Ixodes pacificus, the western black-legged tick, on rodent hosts is often assumed to be constant across various habitats and not dependent on the rodent or predator communities; however, this is rarely tested. The factors that determine tick burdens on key reservoir hosts are important in estimating Lyme disease risk because larger tick burdens can amplify pathogen transmission. This study is the first to empirically measure I. pacificus larval burdens on competent reservoir hosts as a function of community factors such as rodent diversity, predator diversity, and questing tick abundance. Rodents were live trapped at oak woodland sites to collect tick burdens and tissue samples to test for infection with Borrelia burgdorferi sensu lato. We found that N. fuscipes tick burdens were negatively correlated with predator diversity, but positively correlated with questing I. pacificus larvae. In addition, rodent hosts that were infected with B. burgdorferi sensu lato tend to have higher burdens of larval ticks. These results demonstrate that tick burdens can be shaped by variability between individuals, species, and the broader host community with consequences for transmission and prevalence of tick-borne pathogens.