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 <5%=1, 5
to 10% = 2, >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
•
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 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
•
•
•
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