Dr Stephen BattersbyPresident CIEH & Chair, CIEH National Pest Advisory Panel

Climate change and rat populations - is this a further threat to public health?

• 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. Capillariasis

Toxocara spp. Toxocariasis

Hymenolepis nana Rat tapeworm

Trichuris spp.* Diarrhoeal disease etc

Hymenolepis spp. Diarrhoeal disease etc

Taenia spp. Diarrhoeal disease etc

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

Rats & Public Health

Bacteria Diseases in Humans

Leptospira spp. Leptospirosis

Listeria spp. Listeriosis

Yersinia enterocolitica

Yersiniosis

Pasteurella spp. Pasteurellosis

Pseudomonas spp. Melioidosis

Borrelia burgdorferi Lyme disease

Coxiella burnetii (antibodies)

Q Fever

Salmonella spp. Salmonellosis

Vibrio spp. 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. Coccidiosis etc.

Entamoeba spp. 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 <5%=1, 5 to 10% = 2, >10% = 3. No mortality = 0.

Examples of pathogens that may be transmitted by rodents & risk

Disease Agent Carrier or

Reservoir

Pop at

risk

Chance

Severity – human health

Q FeverBacteria,Gammaproteobacteria

Reservoir 3 2 3

Toxoplasmosis

Parasite, Sporozoea

Reservoir3 2 2

E. coli 0157/VTEC

Bacteria,Gammaproteobacteria

Carrier 2 1 3

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

NB. This is a global assessment.

Rural rats

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

Parasite Disease PrevalenceLeptospira spp Leptospirosis 14%

(Weil’s disease)

Cryptosporidium Parvum Cryptosporidiosis 63%

Coxiella burnetii (antibodies) Q Fever 34%

Hantavirus Hantaan-fever 4%

• 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.

Hantavirus

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

• 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?

• 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 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: a public health issue

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

• 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