Urbanization and Infectious Diseases

What role does urbanization have to play in the changing epidemiology and emergence of infectious diseases? These slides accompanied my interactive lecture taken as a part of the Environmental Health module of the MPH course for the students at the Indian Institute of Public Health, Delhi.

1. Pranab Chatterjee MD
Senior Research Associate
Public Health Foundation of India
Environmental Health Module IIPH Delhi MPH, 2016-2018
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3. 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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4. 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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5. 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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6. What infectious diseases
may be encouraged by
these settings?
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7. Do you know what
infectious disease
wreaked havoc here?
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8. What infectious diseases may be
encouraged by these settings?
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9. Do you know what
infectious disease was
believed to wreak havoc
here?
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10. 10

11. 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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12. 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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13. 13

14. Cities
Water
related
Sanitation
related
Vector
borne
Respiratory
STIs
HIV
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15. What are your thoughts?
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16. What are your thoughts?
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Image: Nature 406, 762-767 (17 August 2000)
doi:10.1038/35021206

17. 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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18. 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 vectorialcapacity
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19. 19

20. Feb 15: Patient A (index case) had onset of symptoms
Feb 21: Traveledwith family from Guangdong to Hong Kong;
stayed on 9
th
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 11
th
& 14
th
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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21. 21

22. 22

23. 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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24. 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; Culexpipiensprefers man-made
water collections for breeding; Role of birds –the American Robin (Turdusmigratorius)
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25. GROUP WORK: POPULATION GROWTH
RATS AND THE CITY
Transmission of several zoonotic
diseases:
Yersinia pestis
Leptospiraspp
Rickettsia typhi
Streptobacillus moniliformis
Bartonella henselae
Angiostrongyluscantonensis
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.

26. 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

27. Garrett-Jones defined vectorialcapacity as:
VC= vectorialcapacity
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
sporozoiteswithin an infected mosquito)
u= per capita mortality of female mosquitoes
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28. Garrett-Jones defined vectorialcapacity as:
VC= vectorialcapacity
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
sporozoiteswithin 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 vectorialcapacity than rural areas?

29. 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
Dirofilariaimmitis
ZIKA!!!
How did it get into the USA and Europe?
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30. 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
Dirofilariaimmitis
ZIKA!!!
How did it get into the USA and Europe?
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34. Usually urban centershave 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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35. 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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36. Bamako (Mali), Dar esSalaam (Tanzania), Kampala (Uganda)
Schistosoma sppis 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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37. 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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38. Why is dengue such a major
urban problem?
38Image: Nature Reviews Disease Primers
16055 doi:10.1038/nrdp.2016.55

39. 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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41. A social ecological systems
perspective –looking at cities as
couple human-natural systems
Modifiedfrom Wilcox and Gubler
(2005)
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42. Revisiting the initial query?
Did we add to your earlier responses?
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43. Pranab Chatterjee MD
[email protected]
Ext: 4551
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