Rats as sources of multidrug-resistant Enterobacteriaceae in animal production environments

Rattus norvegicus and Rattus rattus are commensal pest rodents, considered reservoirs and vectors of zoonotic pathogens. In livestock farms, the wide use of antimicrobials and their release into the environment lead to high long-term residual concentrations, which may in turn lead to the occurrence of antimicrobial resistance (AMR). Farm environments serve as AMR sources, resulting in the transmission of antimicrobial-resistant bacteria and their AMR genes of livestock origin into wildlife. This study aimed to analyse the profile of enterobacteria carrying AMR determinants in rats captured in livestock farms to determine their potential vectors as for the spread of AMR. To this end, 56 rats (52 R. norvegicus and 4 R. rattus) were live-trapped on 11 farms (pig, dairy, poultry and mixed farms) located in central Argentina, from spring 2016 to autumn 2017. From 50 of the R. norvegicus individuals and three of the R. rattus individuals found in 10 of the farms, we isolated 53 Escherichia coli and five Salmonella strains. Susceptibility to antimicrobials, genotypic profiles, minimal inhibitory concentration of colistin and the presence of mcr-1 and genes encoding extended-spectrum β-lactamase (ESBL) were determined. Of the 58 isolates not susceptible to different antimicrobial classes, 28 of the E. coli strains and two of the Salmonella strains were defined as multi-drug resistant (MDR). S. Westhampton and S. Newport recovered were not susceptible to ampicillin or all the cephems tested. One of the E. coli obtained showed resistance to colistin and harboured the mcr-1 gene, demonstrated by PCR and conjugation. In two ESBL-producing Salmonella isolated from rats, CTX-M-2 genes were responsible for the observed resistance to third-generation cephalosporins. The MDR E. coli isolates showed several different resistance patterns (23), although some of them were the same in different individuals and different farms, with six resistance patterns, evidencing the dispersion of strains. These findings suggest that rats play a role in the dissemination of AMR determinants between animal, humans and environmental reservoirs.

Malayan kraits (Bungarus candidus) show affinity to anthropogenic structures in a human dominated landscape

Animal movement can impact human-wildlife conflict by influencing encounter and detection rates. We assess the movement and space use of the highly venomous and medically important Malayan krait (Bungarus candidus) on a suburban university campus. We radio-tracked 14 kraits for an average of 114 days (min: 19, max: 218), during which we located individuals an average of 106 times (min: 21, max: 229) each. Most individuals displayed some level of attraction to buildings (n = 10) and natural areas (n = 12); we identified a similar unambiguous pattern of attraction to buildings and natural areas at the population level (of our sample). Snakes remained in shelter sites for long durations (max: 94 days) and revisited sites on average every 15.45 days. Over 50% of locations were within human settlements and 37.1% were associated with buildings. We found generally seasonal patterns of activity, with higher activity in wet seasons, and lower activity in the hot season. These results show frequent proximity between Malayan kraits and humans at the university; thereby, suggesting a near constant potential for human-wildlife conflict. Despite the fact that no snakebites from this species occurred at the university during our study period, substantial education and awareness training should be considered to ensure continued coexistence on campus.

Effects of anticoagulant rodenticide poisoning on spatial behavior of farm dwelling Norway rats

Commensal rodent species cause damage to crops and stored products, they transmit pathogens to people, livestock and pets and threaten native flora and fauna. To minimize such adverse effects, commensal rodents are predominantly managed with anticoagulant rodenticides (AR) that can be transferred along the food chain. We tested the effect of the uptake of the AR brodifacoum (BR) by Norway rats (Rattus norvegicus) on spatial behavior because this helps to assess the availability of dead rats and residual BR to predators and scavengers. BR was delivered by oral gavage or free-fed bait presented in bait stations. Rats were radio-collared to monitor spatial behavior. BR residues in rat liver tissue were analyzed using liquid chromatography coupled with tandem mass spectrometry. Norway rats that had consumed BR decreased distances moved and had reduced home range size. Treatment effects on spatial behavior seemed to set in rapidly. However, there was no effect on habitat preference. Ninety-two percent of rats that succumbed to BR died in well-hidden locations, where removal by scavenging birds and large mammalian scavengers is unlikely. Rats that ingested bait from bait stations had 65% higher residue concentrations than rats that died from dosing with two-fold LD₅₀. This suggests an overdosing in rats that are managed with 0.0025% BR. None of the 70 BR-loaded rats was caught/removed by wild predators/scavengers before collection of carcasses within 5-29 h. Therefore, and because almost all dead rats died in well-hidden locations, they do not seem to pose a significant risk of AR exposure to large predators/scavengers at livestock farms. Exposure of large predators may originate from AR-poisoned non-target small mammals. The few rats that died in the open are accessible and should be removed in routine searches during and after the application of AR bait to minimize transfer of AR into the wider environment.

Norway rat (Rattus norvegicus) ectoparasites in livestock production systems from central Argentina: Influencing factors on parasitism

Haematophagous ectoparasites are worldwide vectors of many zoonotic bacterial diseases, both emerging and re-emerging, whose incidences are rising. Livestock development alters different environmental characteristics such as the microclimate of a site, changing the availability, density and susceptibility of the hosts to pathogens and vectors, indirectly influencing the spread and persistence of a disease within an ecosystem. The Norway rat (Rattus norvegicus), the most abundant vertebrate pest species found on livestock farms from Argentina, is a reservoir for several important zoonotic bacteria and may harbor ectoparasite species, which act as their vectors. Even though the Norway rat is widely known for its role as an ectoparasite host, the ecological characteristics of their ectoparasite communities and the related factors with parasitism on livestock farms have never been described. In the present study, we describe the ectoparasite community in Norway rats from central Argentina livestock farms, while also depicting the influencing factors on both ectoparasite occurrence and abundance. Ectoparasites were collected from rats captured in 20 sites from Buenos Aires province, between the winter of 2016 and the summer of 2018. A total of 1441 ectoparasite individuals were collected from 159 Norway rat individuals [Total ectoparasite prevalence = 69.2%; Mean ectoparasite specimen abundance (± CI) = 9.06 ± 2.32 ectoparasite individuals per rat; Mean ectoparasite specimen intensity (±CI) = 13.10 ± 3.08 ectoparasite individuals per infested rat found]. Ectoparasite assemblage consisted of four cosmopolitan species, recognized for their sanitary relevance: mites (Laelapidae: Laelaps nuttalli and Laelaps echidninus), lice (Polyplacidae: Polyplax spinulosa) and fleas (Pulicidae: Xenopsylla cheopis). We observed higher Norway rat abundance in sites related to higher ectoparasite occurrence and abundance frequencies on the rats. Additionally, ectoparasites were more abundant on rats in warm seasons and on male individuals, over female rats. Moreover, the geographical location of the studied sites influenced the ectoparasite assemblage structure observed on the rats. This study broadens the knowledge on the role of Norway rats as zoonotic ectoparasites hosts and analyzes the drivers influencing ectoparasite occurrence and abundance on the most populated region of Argentina, which is also the region with the most intensive livestock farming. Therefore, this survey may assist in evaluating potential risks for humans and generate effective sanitary control strategies for ectoparasite-borne infectious diseases.

Small-mammal assemblages in piggeries in a developing country: relationships with management practices and habitat complexity

Abstract ContextPig production is increasing in developing countries and is increasing the coexistence of different production systems regarding management practices. Small mammals can cause major economic and sanitary problems on pig farms. The interactions among small mammals, production practices and habitat complexity have been sparsely studied. AimsThe aim was to compare small-mammal assemblages on extensive and intensive pig-production systems, and to analyse the relationship with environmental characteristics and management practices. MethodsSeasonal live-trapping of small mammals within 18 farms (under intensive or extensive management) was performed in central Argentina, simultaneously with a survey of environmental and management practices. Multiple regression analyses were performed to assess the relation between infestation levels and environmental characteristics. Key results In total, 472 small mammals were captured, including the exotic murids Rattus norvegicus, R. rattus and Mus musculus, three native sigmodontines, namely, Akodon azarae, Oligoryzomys flavescens and Oxymycterus rufus, and two native marsupials, namely, Didelphis albiventris and Lutreolina crassicaudata. The location of waste deposits, the density of cats, the frequency of rodent control and the way pig food was stored influenced wild small-mammal abundance; exotic rodent species were lower when the density of cats increased. Rattus norvegicus was more abundant where rodent control was not frequent or null, contrary to M. musculus. Both species were more abundant in food and pig sheds, whereas native species were associated with vegetated areas outside of sheds. Also, A. azarae was associated with the density of pigs. Didelphis albiventris was more abundant on extensive farms, whereas L. crassicaudata was captured on intensive farms. Conclusions Small-mammal abundance did not respond to the type of production system per se, but exotic species abundance was influenced by management decisions. The most important human behaviours related to exotic rodent infestation were the possession of cats, the frequency of rodent control and the way waste and pig feed were managed. Implications Our findings highlighted the need for integrated studies on factors influencing the dynamics of rodent populations in commercial piggery systems, for the development of effective pest management. Management recommendations need to assess environmental complexity and human behaviour as important moderators of the population dynamics of small mammal species in and around piggeries.

Small rodent species on pig and dairy farms: habitat selection and distribution

BACKGROUND

Rodent species are common in livestock production systems, and some of them are considered serious pests because of the sanitary problems and economic losses they cause. Information about microhabitat selection by rodent species in livestock production systems is necessary for understanding rodent requirements and to contribute to effective prevention and development of control measures for pest rodent species. In this work we study microhabitat selection by rodent species that inhabit pig and dairy farms in central Argentina. Rodent trapping was conducted over three years (2008-2011) on 18 livestock farms, each one sampled seasonally during one year. To study habitat selection, microhabitat characterizations were performed describing 22 environmental variables in captured sites and random trap sites without captures.

RESULTS

With a trapping effort of 7333 Sherman and 7026 cage live trap-nights, 444 rodents of seven species were captured (including the murine pest species Rattus norvegicus, R. rattus and Mus musculus and four native species). The three murines selected characteristics related to building structure and/or to food sources availability/proximity, while Akodon azarae selected sites with tall herbatious vegetation.

CONCLUSIONS

We identified microhabitat characteristics that explain habitat distribution of small rodent species in these complex farm systems. This study contributes to broaden the integrated pest management of rodent pest species and could also contribute to the reduction of the use of rodenticides in these systems. © 2018 Society of Chemical Industry.