Beyond abundance: How microenvironmental features and weather influence Bartonella tribocorum infection in wild Norway rats (Rattus norvegicus).

Norway rats (Rattus norvegicus) inhabit cities worldwide and carry a number of zoonotic pathogens. Although many studies have investigated rat-level risk factors, there is limited research on the effects of weather and environment on zoonotic pathogen transmission ecology in rats. The objective of this study was to use a disease ecology approach to understand how abiotic (weather and urban microenvironmental features) and biotic (relative rat population abundance) factors affect Bartonella tribocorum prevalence in urban Norway rats from Vancouver, British Columbia, Canada. This potentially zoonotic pathogen is primarily transmitted by fleas and is common among rodents, including rats, around the world. During a systematic rat trap and removal study, city blocks were evaluated for 48 environmental variables related to waste, land/alley use and property condition, and rat abundance. We constructed 32 weather (temperature and precipitation) variables with time lags prior to the date we captured each rat. We fitted multivariable logistic regression models with rat pathogen status as the outcome. The odds of a rat testing positive for B. tribocorum were significantly lower for rats in city blocks with one or more low-rise apartment buildings compared to blocks with none (OR = 0.20; 95% CI: 0.04-0.80; p = .02). The reason for this association may be related to unmeasured factors that influence pathogen transmission and maintenance, as well as flea vector survival. Bartonella tribocorum infection in rats was positively associated with high minimum temperatures for several time periods prior to rat capture. This finding suggests that a baseline minimum temperature may be necessary for flea vector survival and B. tribocorum transmission among rats. There was no significant association with rat abundance, suggesting a lack of density-dependent pathogen transmission. This study is an important first step to understanding how environment and weather impacts rat infections including zoonotic pathogen ecology in urban ecosystems.

Polioencephalomalacia and Heart Failure Secondary to Presumptive Thiamine Deficiency, Hepatic Lipidosis, and Starvation in 2 Abandoned Siamese Cats.

Two 4-year-old spayed female Siamese cats were seized by the British Columbia Society for the Prevention of Cruelty to Animals after confinement to an abandoned housing unit without food for 9 weeks. One cat was found dead, and the second was euthanized within 24 hours due to neurologic deterioration despite therapy. Polioencephalomalacia of the caudal colliculus, hepatic lipidosis, cachexia, and congestive heart failure with cardiomyocyte atrophy were identified in both cats through postmortem examination and attributed to a prolonged period of starvation. Brain lesions were likely the result of thiamine deficiency (Chastek paralysis), which can be associated with both malnutrition and liver disease. This case highlights the importance of thiamine supplementation during realimentation of cats with hepatic lipidosis. Heart failure resulting from cachexia may have contributed to the death of the first cat and the morbidity of the second cat.

Respiratory Pathology and Pathogens in Wild Urban Rats (Rattus norvegicus and Rattus rattus).

Norway (Rattus norvegicus) and black rats (Rattus rattus) are common peridomestic species, yet little is known about wild rat ecology, including their natural diseases. We describe gross and histological lesions in the respiratory tract of a sample of 711 wild urban rats. A subset was examined for 19 distinct categories of histological lesions in the respiratory tract. Testing for known respiratory pathogens included serology and polymerase chain reaction (PCR) of lung samples. Grossly evident lesions were rare (8/711; 1%). Upper respiratory tract inflammation was present in 93 of 107 (87%) rats and included rhinitis, submucosal and periglandular lymphoplasmacytic tracheitis, and/or tracheal intraluminal necrotic debris and was significantly associated (P < .05) with the presence of cilia-associated respiratory bacillus (CARB), Mycoplasma pulmonis, and increased body mass (odds ratio [OR] = 1.09; 95% confidence interval [CI] = 1.05-1.14 per 10 g). Within the lungs, peribronchiolar and/or perivascular lymphoplasmacytic cuffs were present in 152 of 199 rats (76%) and were also significantly associated (P ≤ .02) with CARB, M. pulmonis, and increased body mass (OR = 1.20; 95% CI = 1.14-1.27 per 10 g). Rats were frequently coinfected with M. pulmonis and CARB, and lesions associated with these pathogens were histologically indistinguishable. Pneumocystis sp was detected in 48 of 102 (47%) rats using PCR but was not significantly associated with lesions. This description of pathology in the respiratory system of wild rats demonstrates that respiratory disease is common. Although the impact of these lesions on individual and population health remains to be investigated, respiratory disease may be an important contributor to wild rat morbidity and mortality.

Survey of cardiovascular pathology in wild urban Rattus norvegicus and Rattus rattus.

Norway (Rattus norvegicus) and black rats (Rattus rattus) are common commensal pests, yet little is known about the ecology of wild rats, including their natural diseases. We describe microscopic cardiovascular pathology in a subset of a sample of 725 wild urban rats. Changes observed in the pulmonary blood vessels (n = 199) included arteriolar medial hypertrophy (20.1%, n = 40) and blood vessel mineralization (19.1%, n = 38). Microscopic changes in the heart (n = 200) included myocarditis (33.5%, n = 67), fibrosis (6.0%, n = 12), mineralization (9.5%, n = 19), myocardial degeneration (22.0%, n = 44), and right ventricular hypertrophy (4.5%, n = 9). Rats with myocarditis, fibrosis, or myocardial degeneration were grouped into a composite variable: cardiomyopathy. Statistical analysis showed that the odds of being affected by cardiomyopathy were greater in male rats (odds ratio [OR] = 2.49; 95% confidence interval [CI] = 1.12-5.55) and heavier rats (OR = 1.14; 95% CI = 1.09-1.20). The odds of pulmonary arteriolar medial hypertrophy was greater in sexually mature rats (OR = 2.35; 95% CI = 0.75-7.36), while the odds of pulmonary vessel mineralization were greater in heavier rats (OR = 1.07; 95% CI = 1.03-1.11) and in black rats (OR = 5.35; 95% CI = 1.62-17.69) compared to Norway rats. To our knowledge, this is the first detailed description of pathology in the cardiovascular system of wild rats and demonstrates that cardiovascular disease is common. The impact of these lesions on individual and population health remains to be investigated.

Destructive polyarthropathy in aborted bovine fetuses: a possible association with Ureaplasma diversum infection?

Severe destructive polyarthropathy with fibrillation and erosion of articular cartilage, deformation of articular surfaces, and proliferation of periarticular soft tissue was diagnosed in 5 bovine fetuses aborted in the last trimester. There was involvement of a single coxofemoral joint in 2 fetuses, both elbows, and a stifle in 1, both stifles and tarsal joints in another, and, in the most severely affected fetus, both hips, stifles, and shoulders as well as 1 carpus. In affected joints, the articular cartilage was irregularly reduced in thickness and contained fibrovascular tissue and, in some cases, inflammatory cells and fibrin. Four of 5 fetuses had microscopic placentitis; all had mild lymphoplasmacytic conjunctivitis. Ureaplasma spp. was identified in 4 cases by polymerase chain reaction or culture. Fetal arthropathy and Ureaplasma diversum-associated joint pathology have not been previously reported in the veterinary literature; however, other Ureaplasma spp. are known to cause reproductive disease and arthritis in humans.