Talk_Steve Battersby - North West Zoonoses Group

Climate change and rat populations - is this a further threat to public health? Dr Stephen Battersby President CIEH & Chair, CIEH National Pest Advisory Panel

• CIEH Established the National Pest Advisory Panel to promote pest management as a public health issue • The CIEH was also leading supporter of the WHO Project to produce the book on the “Public Health Significance of Urban Pests”

Publications

www.euro.who.int/InformationSources/Publications/Catalogue/20080617_9 & www.cieh-npap.org/documents/Urban-pests-publichealth-significanceJULY08.pdf

Recent Studies •

Rats infected with a wider range of parasites than thought hitherto

•

However studies so far indicate the prevalence of parasites in brown rats may be less in urban rats than in rural rats

•

Possibly due to sufficient predation to prevent population densities matching those on some farms

Rats & Public Health: Some Parasites & Diseases Parasite

Diseases in Humans

Helminths

Capillaria spp. Toxocara spp. Hymenolepis nana Trichuris spp.* Hymenolepis spp. Taenia spp.

Capillariasis Toxocariasis Rat tapeworm Diarrhoeal disease etc Diarrhoeal disease etc Diarrhoeal disease etc

* Only parasite with greater prevalence in urban rats than rural rats

Rats & Public Health Bacteria

Diseases in Humans

Leptospira spp. Listeria spp. Yersinia enterocolitica Pasteurella spp. Pseudomonas spp. Borrelia burgdorferi Coxiella burnetii

Leptospirosis Listeriosis

Salmonella spp. Vibrio spp.

Salmonellosis

(antibodies)

Yersiniosis Pasteurellosis Melioidosis Lyme disease Q Fever

Diarrhoeal disease etc

Rats & Public Health Protozoa

Diseases in Humans

Cryptosporidium parvum

Cryptosporidiosis

Toxoplasma gondii

Toxoplasmosis

Babesia spp.

Babesiosis

Sarcocystis spp.

Sarcosporidiosis

Coccidia & Eimeria spp. Entamoeba spp.

Coccidiosis etc. Amoebic dysentery

Virus (antibodies) Hantavirus

Hantaan-fever

Explanation for next slide • Reservoir: rodents harbour disease-causing organisms and serve as potential sources of disease outbreaks, but always via a vector • Carrier: rodent that shows no or limited symptoms of a disease but harbors the disease-causing agent and is capable of passing it directly onto humans • Population at-risk: focal = 1, regional = 2, >2 continents = 3 • Chance: chance of contracting the disease (all pathways, not only via rodents): small chance = 1, moderate chance = 2, high chance = 3 • Human health: Mortality without treatment 10% = 3. No mortality = 0.

Examples of pathogens that may be transmitted by rodents & risk Disease

Agent

Q Fever

Bacteria, Gammaproteobacteria

Toxoplasmosis Parasite, Sporozoea E. coli 0157/VTEC

Bacteria, Gammaproteobacteria

Carrier or Reservoir

Pop at risk

Chance

Severity – human health

Reservoir

3

2

3

3

2

2

2

1

3

Reservoir

Carrier

NB. This is a global assessment. Based on: Meerburg BG, Singleton GR, & Kijlstra A, 2009, Rodent-borne diseases and their risks for public health, Critical Reviews in Microbiology, 2009; 35(3): 221–270

Rural rats The study of farm rats found the following parasites (amongst others) (Webster & MacDonald, 1995) Parasite

Leptospira spp

Disease Leptospirosis (Weil’s disease)

Cryptosporidium Parvum Cryptosporidiosis Coxiella burnetii (antibodies)

Hantavirus

Q Fever

Hantaan-fever

Prevalence 14%

63% 34%

4%

Hantavirus •

In Baltimore USA, Hantavirus antibody prevalence rates of 50%+ have been found (See: Easterbrook JD, Shields, T Klein SL & Glass GE, Vector Borne Zoonotic Dis. 2005 Fall;5(3):296-9: Yanagihara R, Rev Infect Dis 1990 May Jun;12(3):449-57R: and Childs JE, Korch GW, Glass GE, LeDuc JW, Shah KV Am J Epidemiol. 1987 Jul;126(1):55-68. for example)

•

Humans are the only known disease end point of the infection.

Buenos Aires Study • 10 sites sampled & 151 R.norvegicus trapped • Hantavirus seroprevalence was 11.9% varying between 0% and 26.1% depending on site • Hantavirus infections geographically widespread in city • They have been enzootic for at least 20 years (Cueto GR, Cavio R, Bellomo C, Padula PJ, Suarez OV, 2008, Trop Med & Int Hlth, 13, 1, 46-51.)

Rat problems – a question of place • Rat infestations an indication of a degraded environment and recent studies show an association with: • Older housing in poor condition • Multi-occupied buildings (and therefore should be a • •

consideration in management particularly of HMOs) Ageing and dilapidated infrastructure Poor environment – litter, dereliction, neighbourhoods of social deprivation etc

• If treatment by local authorities depends on

complaint – these may be areas where people less likely to complain

Implications

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In urban areas rats are living in closer proximity to the human population than farm rats

•

Climate change and inadequate or inappropriate interventions by municipal authorities could lead to increased population densities in some urban areas

•

This in turn could lead to increased prevalence of parasites and further enhanced risk to the health of those already likely to have lower health status

Climate change and human behaviour •

Alien invasive species are a large threat to biodiversity (Mack et al. 2000; IUCN 2008), and the economic damage they cause exceeds 5% of the global gross product (Pimentel 2002).

•

Synanthropic rats reflect human activity and are one of the most invasive species – will global travel etc increase infections within rodent population?

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Human behaviour may also change with climate, bringing closer contact between rats and humans

Climate change and human behaviour • Increased water-use and flooding with sewers running at full capacity – causing rats to abandon sewerage system • Lack of water compromises personal hygiene • Increased outdoor living • More food waste not correctly stored and disposed of (and spoilage) • Doors etc left open compromising “pest proofing” of buildings (dwellings) • More “self-treatment” if no free LA service or companies expensive

Pest Management: a public health issue • “Pest control” has replaced the notion of vector control and management of pests, as part of public health management? • Has technology and pressure on resources led to treating symptoms not causes? • Are local authorities and the pest management industry prepared?

Pest Management: a public health issue • The integrated approach to pest management has all too often been forgotten – does charging compromise this? • Rodents are also often an indication of a degraded environment whilst posing a risk to the health of those whose health status may already be compromised • The integrated approach to pest management has all too often been forgotten – does charging compromise this?

Pest management and public health • Effective pest management cannot be based merely on responding to complaint • Strategic approach required and also a matter of health equity • Whatever infestations rates are (locally and nationally) there will be “hot spots” • Better understanding of respective roles of various public health agencies needed, but also better co-operation

Pests - health and well-being • Rodent pests and urban sprawl (urbanisation) + climate change increases risks • Strong evidence for relationship between allergic asthma and domestic exposure to cockroaches, mice, rats and dust mites is strong • Presence of rodents has been a reflection of a degraded environment – climate change could exacerbate this • Presence of pests can also impact mental health (stress)

Conclusion •

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Rats are infected with more parasites than previously thought – contaminating the environment Location more than total numbers may be the issue but we will have to live with the “concisest tenant” (Emily Dickinson) - will this be closer than we would like? Climate change will increase pressures on sanitation and good hygiene, so will increase risks

Thank you