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

Abstract

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] ¼ 1.09; 95% confidence interval [CI] ¼ 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 ¼ 1.20; 95% CI ¼ 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.Keywords cilia-associated respiratory bacillus; lung; Mycoplasma pulmonis, pathology; Pneumocystis; rats; Rattus norvegicus; Rattus rattus; respiratory diseases; wild Norway and black rats (Rattus norvegicus and Rattus rattus) are cosmopolitan peridomestic species that are well adapted to living in urban habitats.12 Negative impacts of rats on human society range from economic losses through agricultural crop destruction to zoonotic diseases. 12,13,22 Even though rats have lived in cities with people for centuries, many details of urban rat ecology remain unexplored. Specifically, little is known about the causes of natural morbidity and mortality in rats.The life span of wild urban rats is considerably shorter than that of laboratory rats, with few individuals living beyond 1 year of age.12 Conversely, laboratory rats live up to 3 years. 43Factors contributing to the rapid population turnover among wild rats are unclear. Due to the high fecundity of rats, predation and human rat control activities, including trapping and poisoning, have limited effects on population size. 12 Mortality associated with resource competition does not explain why mature rats die, since they would be expected to outcompete juvenile rats.12 Natural disease may be a key component to

The devil is in the details—Host disease and co‐infections are associated with zoonotic pathogen carriage in Norway rats (Rattus norvegicus)

“…Based on univariable analysis, the following variables were significantly associated with L. interrogans : Capillaria hepatica in the liver, bite wounds, other macroscopic lesion(s), cardiomyopathy, non‐glandular stomach lesions, thyroid goitre, iBALT, tracheitis, urinary crystals and nematode in any organ (Table ). Tracheitis and iBALT in the lungs are related variables since both lesions are attributable to bacterial respiratory infections (cilia‐associated respiratory bacillus and/or Mycoplasma pulmonis (Rothenburger, Himsworth, Clifford, et al, ). Similarly, data for C. hepatic in the liver are captured by nematode in any organ variable.…”

“…Cardiomyopathy is a known cause of mortality in laboratory rats and is suspected to similarly impact wild rat health (Keenan, Soper, Smith, Ballam, & Clark, ; Rothenburger, Himsworth, Treuting, & Leighton, ). Tracheitis, associated with respiratory pathogens (CAR bacillus and M. pulmonis ), is indicative of respiratory disease (Rothenburger, Himsworth, Clifford, et al, ). Bite wounds ranged in severity but were often infected (Himsworth, Zabek, et al, ).…”

Immune defense of wild-caught Norway rats is characterized by increased levels of basal activity but reduced capability to respond to further immune stimulation

“…Migration of leukocytes to tissues is a normal response to a variety of tissue insults, primarily microbial penetration, which may compromise cell/tissue integrity and is necessary for immune surveillance and effector functions (Friedl & Weigelin 2008;Nourshargh & Alon 2014). Indeed, wild rats harbor a variety of pathogens (Easterbrook et al 2007;Meerburg et al 2009;Rothenburger et al 2015;Pépin et al 2016) and our preliminary microbiological survey of lungs, liver and kidneys showed the presence of several pathogenic bacteria as well. Although immune-based activities in tissues can be taken as related to microbial infection, the influence of environmental toxicants shall not be excluded.…”

Rodentia

“…This agent acts synergistically with other respiratory pathogens including Mycoplasma pulmonis, Sendai virus, coronavirus, Streptococcus pneumoniae, Corynebacterium kutscheri, Bordetella bronchiseptica, Klebsiella pneumoniae, or Pasteurella spp. Lesions include suppurative to mucopurulent bronchopneumonia, perivascular and bronchiolar lymphoid hyperplasia, rhinitis and lymphoplasmacytic tracheitis in free-ranging, pet and laboratory rats Rothenburger et al, 2015b). Coinfection of CAR bacillus and mycoplasmas has been reported in rats and spinifex hopping mice with pneumonia (Mackie et al, 2001).…”

“…Histologic lesions include peribronchial lymphoid cuffing with BALT hyperplasia; neutrophilic bronchopneumonia; type II pneumocyte hyperplasia of alveolar epithelium; and emphysema; bronchiectasis is a characteristic finding. Histology alone cannot differentiate M. pulmonis and CAR bacillus respiratory infections (Rothenburger et al, 2015b). Other lesions associated with M. pulmonis include endometritis, salpingitis, and perioophoritis.…”