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Pranab Chatterjee MD
Senior Research Associate
Public Health Foundation of India
Environmental Health Module IIPH Delhi MPH, 2016-2018
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Urbanization and Infectious Diseases by Pranab Chatterjee is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Materials provided “AS IS”; no representations or warranties provided. User assumes all responsibility for use, and all liability related thereto, and must independently review all materials for accuracy and efficacy. May contain materials owned by others. User is responsible for obtaining permissions for use from third parties as needed.
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Your name, your academic background, why you chose to do the Master’s in Public Health and your vision/ambition as a Public Health Specialist in the making!
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Explore the impact of urbanization on infectious disease emergence and epidemiology and understand interaction between urbanization and infectious disease emergence and transmission patterns
Understand research approaches to study the impact of urbanization on infectious diseases
This will be a task-oriented, hands-on, group-session based activity!
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Breakout Group Discussion. Form two or three groups. Each group should ideally have someone with a health-related background.
This is to help us evaluate the baseline understanding and build from there.
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What infectious diseases
may be encouraged by
these settings?
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Do you know what
infectious disease
wreaked havoc here?
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What infectious diseases may be encouraged by these settings?
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Do you know what
infectious disease was
believed to wreak havoc
here?
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According to census of India:
All statutory places with a municipality, corporation, cantonment board or notified town area committee
A place satisfying the following three criteria simultaneously:
Minimum population of 5000
At least 75% of the male working population engaged in non-agricultural pursuits
Density of population 400/sq.km or 1000/sq. mile
Urbanization: the gradual increase in the proportion of people living in urban areas, and the ways in which each society adapts to the change
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28 megacities (>10 million population) in 2016: projected to reach 41 by 2030
850 cities with 500,000 population by 2030 – most in Asia and Africa
60%+ of the global population residing in urban areas by 2030
Average daily migration to cities: 180,000
Refugee crises from failing nations and conflict zones add to the pressure
Extreme connectivity: Nothing is local anymore…
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Cities
Water related
Sanitation related
Vector borne
Respiratory
STIs
HIV
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What are your thoughts?
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What are your thoughts?
16Image: Nature 406, 762-767 (17 August 2000)
doi:10.1038/35021206
Urbanization is not just about growing cities and rural-to-urban migrations
What other factors related to the growth of cities can you think of?
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Urbanization is not just about growing cities and rural-to-urban migrations
What other factors related to the growth of cities can you think of?
Globalization
Climate change
Population growth/Overcrowding/Congestion
Vector potentiation or increased vectorial capacity
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Feb 15: Patient A (index case) had onset of symptoms
Feb 21: Traveled with family from Guangdong to Hong Kong; stayed on 9th Floor of Hotel M
Feb 22: Pt A admitted to hospital 2; dies on Feb 23
By Feb 28: 4 HCWs, 2 family members fall sick – one dies
March 25: Cluster of 13 persons with suspected/probable SARS are known to have stayed at hotel M. 10 in hotel on same day – 2 others (L, M) stayed when 3 of the 10 were staying in hotel M
9 of 13 patients stayed on floor 9; 1 each on 11th & 14th floors; 2 on 9 &14 both
Patient B index patient for Hanoi involving 59 HCWs and close contacts and also is linked to one case in Thailand.
Patients C, D, and E associated with 70 cases in Singapore and three cases in Germany.
Patient F linked with 16 other cases in Toronto
Patients H and J are linked with outbreaks among HCWs in other hospitals in Hong Kong. Patient L appears to have become infected during his stay at hotel M, with subsequent transmission to his wife, patient M.
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Black fly needs fast running water to reproduce
The vector flies can be spread by strong winds
Global warming and changing precipitation patterns create more breeding sites for the black fly (Mills, 1995)
Increased vector population = Increased disease risks
What might be causing such changes?
Deforestation for urban agriculture
Cities growing into river-adjacent areas with high vector concentration
Re-direction of river water through irrigation channels to peri-urban and urban agriculture
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Schistosomiasis Spread through growing population of snails!
African Trypanosomiasis Changing vegetation cover due to changing environmental temperature and humidity
Tick-borne infections Warmer climates favour spread of ticks carrying Lyme disease
Cooler climates favour spread of ticks carrying Rocky Mountain Spotted Fever
St. Louis Encephalitis Higher temperature increase vector (mosquito) efficacy in spreading the infection
West Nile Virus Stagnant water encourages vector (mosquito) breeding; Culex pipiens prefers man-made
water collections for breeding; Role of birds – the American Robin (Turdus migratorius)
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GROUP WORK: POPULATION GROWTHRATS AND THE CITY
Transmission of several zoonotic diseases:
Yersinia pestis
Leptospira spp
Rickettsia typhi
Streptobacillus moniliformis
Bartonella henselae
Angiostrongylus cantonensis
Seoul Hantavirus
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Group 1:
What might be the reasons that may cause
explosion of the rat population in cities of
India?
Group 2:
As public health specialists, you have to
create a plan to combat the growing rat
problem in the context of an Indian city. Draft
the components of a rodent control program.
Surveys: A measure of the magnitude of the pest problem and its environmental causes
Tolerance limit: Identifying the level at which a pest causes sufficient damage to be considered as a public health problem
Interventions: Actions taken to mitigate the pest problems:
Educational interventions
Legal or regulatory interventions
Habitat modification interventions
Horticultural/Biologic interventions
Mechanical interventions
Chemical interventions
Elimination of causes of infestation
Monitoring and Evaluation 26
Garrett-Jones defined vectorial capacity as:
VC= vectorial capacity
M= size of the female mosquito population
N= size of the human population
a= daily biting rate of a female mosquito
b= proportion of infected bites on humans which produce an infection
p= probability that a blood meal is taken on a human rather than on an alternative host
n= intrinsic incubation period (number of days required to produce infective sporozoites within an infected mosquito)
u= per capita mortality of female mosquitoes
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Garrett-Jones defined vectorial capacity as:
VC= vectorial capacity
M= size of the female mosquito population
N= size of the human population
a= daily biting rate of a female mosquito
b= proportion of infected bites on humans which produce an infection
p= probability that a blood meal is taken on a human rather than on an alternative host
n= intrinsic incubation period (number of days required to produce infective sporozoites within an infected mosquito)
u= per capita mortality of female mosquitoes
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Using the information in this equation, can you explain why
urban areas may be a better setting for malaria to spread due
to increased vectorial capacity than rural areas?
Native to the tropical and sub-tropical forests; but can be found throughout Europe and Americas now
Lives in close association with man
Flies and feeds in the day time, especially at dusk and dawn
Important vector for several diseases like:
Yellow fever virus
Chikungunya virus
Dengue virus
Dirofilaria immitis
ZIKA!!!
How did it get into the USA and Europe?
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Native to the tropical and sub-tropical forests; but can be found throughout Europe and Americas now
Lives in close association with man
Flies and feeds in the day time, especially at dusk and dawn
Important vector for several diseases like:
Yellow fever virus
Chikungunya virus
Dengue virus
Dirofilaria immitis
ZIKA!!!
How did it get into the USA and Europe?
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Usually urban centers have higher rates of tuberculosis than rural areas
Example:
Impoverished slums of Karachi Pulmonary TB prevalence is 329/100,000 people, compared to the national prevalence of 171/100,000 people
What are the potential reasons?
Overcrowding
Unsanitary living conditions
Addictions, smoking
Poor nutrition status, lower socioeconomic status
Access to healthcare
Higher exposure rates to infective cases
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Snails form an important part of the life cycle
Snails increase in areas with more water, warmth
Many African cities have grown up beside irrigation canals drawn from rivers
Warm temperature also increases infectivity of the pathogen
Global warming further increases risk: 5 million additional cases by 2050 if no steps are taken
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Bamako (Mali), Dar es Salaam (Tanzania), Kampala (Uganda)
Schistosoma spp is endemic to local water bodies
Snail populations on the rise due to environmental conditions
Migrants moving from rural areas endemic for the disease are bringing the infection over to the urban centers
Those migrants who come from non-endemic areas to an endemic area are also at high risk of contracting the illness against which they do not have a natural immunity
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Leishmaniasis:
Evidence from Marrakech, Morocco show that increasing urbanization reduces the population of the Phlebotomine sand flies
What can be the potential reasons?
Hepatitis A
Disease of poverty, seen to be lower in highly urbanised areas compared to more rural or poor urban slums
What can be the potential reasons?
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Why is dengue such a major urban problem?
38Image: Nature Reviews Disease Primers
16055 doi:10.1038/nrdp.2016.55
Group 1:
What are some of the reasons which may cause the dengue outbreaks in Delhi every year?
Group 2:
As a group of public health experts, devise a set of interventions to ensure that Delhi does not experience an outbreak of Dengue this year.
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A social ecological systems perspective – looking at cities as couple human-natural systems
Modifi ed from Wilcox and Gubler(2005)
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Revisiting the initial query?
Did we add to your earlier responses?
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