Carriers and Control

This is very much a work in progress. I will continue to add articles, links, etc. as I find them. Although other animals such as raccoons can be lepto carriers, my primary focus here are rats as that is what vets and myself think are the primary carriers of the leptospriosis in the City of Halifax. There are literally hundreds, if not thousands of news articles about rat problems in Cities around the world. Although I will include some, especially when related to Halifax, I have now turned my focus to finding more academic reports and studies. 
​GENERAL
MY COMMENTS
Studies I have found on rat control in urban areas seem to agree that rat populations can not be effectively controlled by just addressing the problem above ground. Unlike Halifax Water, they seem to believe that rats do indeed live in the sewers; that "sewers provide a protective and stable environment for rats" and "the only way to successfully control rat populations in sewers is the provision of effective maintenance of the sewerage network infrastructure together with proactive sewer baiting programmes." [ Sewer Baiting for Rats in the United Kingdom...] They also say that it is extremely hard to know numbers but "Sewers are historically considered to be the main reservoir for rats (Brooks 1962, CIEH, 2003) with signs of rats above ground being an indication of possible increased population numbers below ground." So, if Halifax citizens are seeing as many rats as being reported then the City has a serious problem that should NOT be ignored by Halifax Council and Halifax Water. 

The problem, as always, is money. Cities are reluctant to put out the money to create an truly effective program for rodent control if they cannot justify the expense. Unfortunately, " limited data are available, and costs to society as a whole are fragmented. Despite evidence of infection with a range of zoonoses, there is little published evidence to enable an assessment of the costs to society attributable to ill- health due to brown rats."​ ​Therefore many Cities either totally leave rodent control up to their citizens or they rely on a reactive, rather then proactive, programs to control rats so as to appear as if they are doing something, but in the end are not successful in controlling the rat population and are therefore wasting time and money.

The use of rodenticides should not be taken lightly. Caution must be applied in their use especially in above ground situations where they can be more of a danger to unintended wildlife, domestic pets and humans. However, while some such as Halifax Water, like to use the "public health safety" as a reason not to bait the sewers at all it is I think note worthy to mention that the paper [Sewer Baiting for Rats in the United Kingdom] presented at the 2014 Proceedings of the English International Conference on Urban Pests states "​Controlling rat populations in the sewer networks across the UK will ultimately reduce the need for second generation anticoagulant rodenticides (SGAR) used to control some above ground rodent populations." So while it might cost more in the short term, as is often the case, in the long term it is more cost effective AND safer for the environment and public health to put the bait in the sewers!
RESOURCES
PAPERS / STUDIES
Sewer Baiting for Rats in the United Kingdom - Is it Money Down the Drain?
Joanne Fozzard, Gai Murphy, David Oldbury, and Sabra Fearon (Editors)
Proceedings of the English International Conference on Urban Pests 2014
Printed by OOK-Press Kft., H-8200 Veszprem, Papai ut 37/a, Hungary

Highlights
  • "The control of rats in urban environments involves more than just dealing with above ground rodent populations. Sewers provide a protective and stable environment for rats with an underground habitat free from predators where they have the freedom to live and breed (Brooks 1962). "
  • "Sewers are historically considered to be the main reservoir for rats (Brooks 1962, CIEH, 2003) with signs of rats above ground being an indication of possible increased population numbers below ground. Research carried out by Battersby et al. (2002) and Bonnefoy et al. (2008) reports that over half of surface rodent infestations in the urban environment are connected to defects in sewers." 
  • " Sewer rats are cunning and will use defects in a sewer as a way of finding an escape into the above ground environment putting public health at greater risk. Controlling rat populations and maintaining a high standard of maintenance of the sewerage  networks can greatly reduce this risk to public health. (Musa and Cheong, 2004, International Pest Control, 2013)"
  • "Proactively baiting in sewers helps to actively monitor and control sewer rat populations, preventing them from becoming an above ground problem using integrated pest management (Murphy and Oldbury, 2002). Many debates have surrounded the effectiveness of proactive baiting in sewers compared with reactive baiting in sewers. It is believed WASCs opt for reactive baiting of sewers in the belief that it is more cost-effective (CIEH, 2003), Murphy and Oldbury (2002) state, reactive sewer baiting did little to actually manage rat populations or solve localised problems. The CIEH believes that proactive sewer baiting is the most cost-effective method for the control of rats in sewers, and in the past local authorities have utilised proactive baiting activities to control these sewer rat populations. "
  • " The research highlights the lack of joint working, co-operation and communication between LAs and WASC which could greatly contribute to increased sewer rat populations reaching the surface as a result of reactive rather than proactive monitoring. "
  • "The only way to successfully control rat populations in sewers is the provision of effective maintenance of the sewerage network infrastructure together with proactive sewer baiting programmes. As with other initiatives, this will require adequate funding and communication between those responsible for the sewers and those with geographical knowledge and public health protection responsibilities. "
  • "Controlling rat populations in the sewer networks across the UK will ultimately reduce the need for second generation anticoagulant rodenticides (SGAR) used to control some above ground rodent populations. Identifying defects in the sewer networks will have a profound impact in reducing the number of sewer rat populations reaching the surface. This in turn will reduce the need to use SGARs and the risk of secondary poisoning to non-target species; something which is constantly monitored by European Union."
Ecology of Leptospira Interrogans in Norway Rats (Rattus Norvegicus) in an Inner-City Neighborhood of Vancouver, Canada
Chelsea G. Himsworth, Julie Bidulka, Kirbee L. Parsons, Alice Y. T. Feng, Patrick Tang, Claire M. Jardine, Thomas Kerr, Sunny Mak, John Robinson, David M. Patrick
Published: June 20, 2013. https://doi.org/10.1371/journal.pntd.ooo2270
Highlights
  • "Leptospira interrogans is a bacterial zoonosis with a worldwide distribution for which rats (Rattus spp.) are the primary reservoir in urban settings."
Author Summary
  • "Urban Norway rats are the source of a number of zoonotic pathogens responsible for significant human illness. Leptospira interrogans is one of these pathogens, and although infection in rats is asymptomatic, humans infected through exposure to the bacterium in rat urine can develop fever, renal failure, and pulmonary hemorrhage. Previous studies of L. interrogans in urban rats have been of limited value because they have not taken into account the complex ecology of the rat populations under study. In this study, we found that the prevalence and distribution of L. interrogans varied greatly between blocks in an inner-city neighborhood (reflecting that rats live in tight-knit colonies with small home ranges) and was not related to rat population size. This suggests that the L. interrogans ‘load’ in a block does not depend on the number of resident rats, but rather on some characteristic intrinsic to that block. Additionally, increased weight, body fat, and bite wounds were found to increase the probability of L. interrogans infection, suggesting that the position of a rat within the colony's social hierarchy may also influence transmission. These factors should be considered before undertaking rat control programs."​
Poison-based Commensal Rodent Control Strategies in Urban Ecosystems: Some Evidence Against Sewer-Baiting
Mughini Gras L, Patergnani M, Farina M
Ecohealth, 2012 Mar; 9(1):75-9. doi: 10.1007/s10393-012-0748-8. Epub 2012 Mar 7
Highlights
  • "Abstract: Sewers are historically considered the main reservoir for commensal rodents, posing threats to urban
    ecosystem health. Aboveground rodent signs are often assumed to give clues to high sewer infestation, which
    can chronically restock surface areas. Thus, current sewer-baiting programmes are mostly reactive, responding
    to increased surface infestation. Conversely, proactive sewer-baiting (regardless of infestation levels) is often
    disregarded because cost-effectiveness is not always addressed. We explored the extent to which the surface
    infestation is related to rodent feeding activity on sewer and surface baits by analysing a set of proactive bait
    records in Bologna city, Italy. Sewer bait intakes were significantly lower than surface ones, suggesting that
    proactive sewer-baiting is generally less effective. As surface infestation increased, probability of recording
    surface bait intake increased significantly but this was not reflected by increased sewer bait intake, suggesting
    that surface infestation is not always a reliable indicator of sewer infestation. This should discourage the use of
    reactive sewer-baiting as a routine strategy. Poison-based control programmes by themselves are scarcely
    predictable and strategically limited, and ideally they should be handled within an ecologically based integrated
    pest management approach for achieving satisfactory results.
Public Health Policy - Can There Be an Economic Imperative? An Examination of one such Issue 
Dr. Stephen A Battersby (Robens Centre for Public and Environmental Health, University of Surrey, England) JEHR (Journal of Environmental Health Research) Vol. 3, Iss. 1, 2004
Highlights
  • "Limited data are available, and costs to society as a whole are fragmented. Despite evidence of infection with a range of zoonoses, there is little published evidence to enable an assessment of the costs to society attributable to ill- health due to brown rats. "
  • "It is concluded that the costs to society should include the social (including health and wellbeing) costs arising from rat infestations and that there is an economic argument for local authorities having effective control strategies for rats in place. "
  • " For society as a whole, it would be worthwhile and economic to spend more on the control of rats in sewers where it can be shown to contribute to reduced aboveground infestations. The difficulty is that private companies will incur the direct costs, but they will not gain any direct benefits. Nor do the companies incur costs resulting from increased rat infestations above ground which are the consequence of inadequate baiting and disrepair of sewers."
  • "Although increased expenditure on rodent control could be justified economically given the costs of damage, current expenditure may also be misdirected as controls are generally reactive, not based on any strategy and therefore potentially wasteful."
  • "However, it is impossible to state whether rats are a problem that needs to be addressed solely on economic grounds. Damage is spread throughout the economy, and remains largely hidden, with no incentive to look deeper. From a governmental perspective, there is sufficient evidence to indicate that the potential exists for substantial economic impact if there are inadequate controls and ineffective strategies."​​
 Urban Rat Infestations and the Risk to Public Health 
Battersby, Stephen A., Robin Parsons, Joanne P. Webter
Journal of Environmental Health Research Vol. 1 Iss. 2 2002
Highlights
  • "The result of ineffective strategies and lack of co-operation from other agencies, as may be occurring in some parts of England and Wales, will be that the rat population and colony densities could increase in urban areas. This is most likely in those areas where there are other social stresses, thereby enhancing the potential for increased parasitic loads within the rat population. This has implications for the health of those communities and could further contribute to inequalities in health."
  • "Several diseases likely to be transmitted by animals are emerging as serious threats to public health. However, the epidemiology of many zoonotic diseases is poorly understood, and even in the UK, baseline data on the prevalence of important zoonoses in wildlife are scarce."
  • "Furthermore, with reports of a deterioration in the integrity of the sewerage infrastructure (Battersby 1998, 1999) coupled with less sewer baiting (Battersby 1998, 1999) rats may have increased opportunity for direct and indirect contact with humans and their companion animals in an urban environment (Bradshaw, 1999)."​
Rodent Control and Public Health: A Description of Local Redent Control Programs
Lisa M Brown, MPH (NACCHO) and Joe Laco, MSEH, RS/REHS (CDC)
HSS Public Access 2017
Highlights
  • "The programs indicated that controlling rodent populations is difficult when it is largely complaint-based. Additionally, participants described a lack of understanding of rodent control by property and business owners, as well as a lack of science and research on the subject."
  • "Some of the most significant challenges for rodent control include a lack of funding and resources. With enough staff, funding, public education, resources, and technology, programs feel that rodent control can be even more successful. "
  • "Framing rodent control as a public health issue, and collaboration amongst public health professionals and their communities will help create long-term and more successful solutions to control rodent populations and keep rodent-borne diseases at bay."​
Information on New Requirements for the Use of Rodenticides
Health Canada March 2015
Highlights
  • "Bait MUST either be placed in tamper-resistant bait stations, in accordance with product label or in locations not accessible, to children, pets, livestock, or non-target wildlife, (e.g. wall voids, below-ground, floor gaps)."
NEWS ARTICLES
WILL CITIES EVER OUTSMART RATS?
States News Service August 9, 2017 Wednesday
Lexis Advance Feb 27th, 2018 search
HIGHLIGHTS
  • "The thing is, no one really knows how many rats there are. Not in New York City, nor Washington, D.C., nor Chicagoall three of which rank among the most rodent-infested cities in the U.S. Even the best numbers available are educated guesses, often based on surveys about calls to 311. It's even more challenging to understand how rats move or anticipate where they will wreak havoc next. But cities have entire teams dedicated to controlling the rat population, and for good reason. The rodents sneak into buildings and subways, nibbling on trash, chewing through cables, and spreading nasty diseases, often while remaining out of sight. Despite the best efforts to deploy traps, poison, and yes even cats, the rodents persist."
  • "But some cities are shifting gears to get one step ahead of the rats. They're teaming up with researchers and computer scientists not just to eliminate the pests, but also to understand, as Blum puts it, "the subtleties of what sustains the populations." And their number one weapon is big data."
  • "To start, the team turns to the city's records on 311 calls about rodent sightingsfor now, that's the most reliable insight for finding rodent hotspots. Then they compare those calls with other city data, including the number of registered businesses (particularly food businesses), apartments (an indication of human density), and the breakdown of the area's landscape (concrete versus "penetrable Earth" like parks). They're looking for patterns that signal favorable conditions for rats, highlighting places where Brown's team could soon find an infestation."
  • "Perhaps not surprisingly, the data team found that 311 calls related to food and shelter were the strongest predictors of a rat infestation. So areas where residents called about sanitation violations or tree debris were most likely to be see a spike in rat complaints."
  • "Not all abatement methods are created equal. Using rodenticide may be more effective in one part of the city while deploying smart, heavy-duty trash bins may be the key in another."
  • "So far, research suggests that rats stay close to their burrows. In fact, the average rat might only venture a few dozen feet in its entire lifetime. They also stick to the same paths, creating "runways" that connect their homes straight to their food source. These trails sometimes appear as streaks of grease left behind from their fur, Brown says, or footpaths embedded in the dirt."
  • "It's still a mystery, though, as to why rat populations can suddenly rebound after being exterminated in an area. "One possibility is that [when] you knock the population down, the survivors have more resources, so they breed faster," Munshi-South says. "Or it could be that there are rats nearby that weren't affected, so they started dispersing into the now empty territory." We just can't say for sure."

​BIRTH CONTROL
ContraPest: New Birth Control Product Approved for Controlling Rats
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