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3.2 Environmental transmission of pathogens
Learning objective: to become familiar with
environmental transmission routes for pathogens,
especially in relation to water and sanitation.
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Infectious disease outbreak among 100 persons
Interviews showed
that all had eaten
e.g. raw lettuce
What brought
EHEC to the lake?
Grass on the
grazing
fields had EHEC
Why were the
cows not sick?
From where did this
At the lab: these
bacteria strain come?
EHEC bacteria were
also found in samples
of irrigation water
At the lab: isolation of bacteria
- and also in a stream in the patients stool and proved
to be the same- EHEC!
Cows were
infected, but
without symptoms
From where did
cows get infected
by EHEC?
100 persons in a small community
were affected by severe diarrhoea,
ten of whom were hospitalised
etcetera
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
:
An example of zoonosis i.e. transmission
from-animal-to-human
3. Irrigation of
lettuces
(no requirement for
analysis of the water)
1. Run-off from
agricultural land
grazed by cattle
infected with EHEC
4. The lettuce was
consumed by a
large number of
individuals –
resulted in 100
cases (some 10
hospitalised)
2. Manure runoff
to river water
At the lab: isolating and comparing
bacteria in samples from patients
and in water samples
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Transmission by animals

Zoonoses




Transmission humans
animals
May cause symptoms or not in animal
Vectors

Insects, rodents, birds – mechanical transport

Birds, wild and domestic animals infected without
symptoms
Intermediate host

Animal necessary for lifecycle of pathogen,
e.g. malaria, schistosomiasis
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Features
of excreta
hygiene
Microorganisms
in -excreta

Urine
 Sterile in body
 Naturally containing
some bacteria after
excretion
 Few diseases
transmitted by urine
 Low risk to handle

Faeces




Naturally containing high
amounts of bacteria
Many diseases
transmitted by faeces
(faecal-oral)
May contain pathogenic
bacteria, viruses,
protozoa or helminths
Significant risk to handle
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
The ”F-diagram”
- main routes for the spread of diarrhoea
(Esrey et al. 1998)
Transmission routes for pathogens in
human excreta
Excreta from humans & animals 1
Land
Runoff
3
Sewage
2
Solid Waste
4
Landfills
Oceans and
Estuaries
5
Rivers and
Lakes
6
Groundwater 7
Shellfish
8
Recreation
9
10
Water
Supply
Crops
Irrigation 11
12
Aerosols
13
Humans
Adapted from Gerba et al. 1975
Pathogens in faeces

May contain bacteria, viruses, parasitic
protozoa and helminths that cause infections

Diarrhoeal disease is the main concern

Faeces should be considered a health
hazard

Need to be treated before use as a fertiliser

Easier to handle and treat if diverted from
other waste fractions
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Sources of faecal indicator bacteria
Origin
Birds and
other animals
Agricultural
runoff and effluent
Recreational use
Domestic
sewage
Industrial
effluent
Stormwater
and surface
water
Leachate
Sea
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Microorganisms in urine

Urine is sterile in the bladder

Freshly excreted urine contains <10 000 bacteria/ml

Urinary tract infections - not transmitted through the
environment

Leptospira interrogans - low prevalence

Salmonella typhi, Salmonella paratyphi - developing
countries, faecal-oral transmission more common

Schistosoma haematobium - fresh water snail
needed for development
low risk for transmission of infectious diseases
through urine
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Origin of pathogens in wastewater
- contribution from different waste fractions

Faeces


Urine


e.g. laundry, washing diapers, from food stuffs
Industry


only a few diseases transmitted through urine
Greywater


the main source of pathogens that cause enteric infections
abattoir, food industry (plant pathogens)
Storm water

e.g. surface run-off – animal faeces
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Ecological Alternatives in Sanitation
Contamination of groundwater
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Contamination of drinking water

Drinking water quality


Contaminated surface- or groundwater


Wastewater outlet, latrines, run-off
Contamination during distribution


Heterotrophic bacteria, E. coli, metals, nitrate
(other aspects are smell, colour)
Growth in pipes, intrusion of wastewater
Contamination of finished water

During storage and handling, e.g. reservoirs, vendors
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Health risks related to untreated
wastewater

Local environmental pollution


High risk of down-stream pollution


Exposure from e.g. swimming and intended household use
Pollution of drinking water sources


Accidental exposure
Surface run-off and ground water infiltration
Contamination of irrigated crops

Exposure during irrigation and at
consumption
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Excretion of pathogens in faeces
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Pathogens in urine and importance of
urine as a transmission route
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Pathogens in mixed wastewater






Small volumes of faeces contaminates large
volumes of clean water
Collection from a large number of persons –
pathogens continuously present
Smaller systems – higher concentration of a
specific pathogen
Treatment not optimized
for killing pathogens
10% of wastewater is
treated (developing countries)
20 million ha (?) irrigated with wastewater
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Pathogens in greywater

Lower concentrations of pathogens here
than in faeces

Faecal origin of pathogens (bathroom and laundry)


Pathogens from food stuffs (kitchen sink)



Shower and bath, washing clothes, washing diapers
Faecally contaminated vegetables (e.g. from irrigation with
wastewater or application of animal manure), soil
Contaminated meat (e.g. chicken)
Health risk from disposal or reuse



Contamination of nearby surroundings
Contamination of drinking and recreational water
Irrigation of crops
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Typical concentrations of microorganisms
in sludge (EC, 2001)
[per g wet weight]
Bacteria
6
E. coli
10
Salmonella
10 -10
Virus
Enterovirus
10 -10
Protozoa
Giardia
10 -10
Helminths
Ascaris
10 -10
Toxocara
10-10
Taenia
5
2
3
2
4
2
3
2
3
2
When treating wastewater, pathogens are being
concentrated in the sludge – not in the effluent
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Possible transmission routes for pathogens
from organic fertilisers (e.g. faeces)
Handling on site
• The handling and reuse of all types of waste products with human
or animal origin involve hygienic risks
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Contamination of food

Contaminated seeds, uptake of pathogens?

Organic fertilisers – human excreta, wastewater,
animal manure

Irrigation – wastewater, contaminated surface
water

Handling and storage

Cooking

Storing of cooked food, growth of pathogens
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden
Waterborne diseases and sanitation
Waterborne diseases are caused by:
- ingestion of water contaminated by human or animal
faeces or urine containing pathogenic bacteria or viruses.
- they include cholera, typhoid, amoebic and bacillary
dysentery and other diarrhoeal diseases.
Sanitation system that involve reuse need to prevent disease
transmission, mainly by:
- protecting ground- and surface water
- safe handling and use of the waste products in agriculture
Caroline Schönning, Swedish Institute for Communicable Disease Control, Solna, Sweden