Emerging infections in historical context, geographical spread of infections, human demographics and behaviour, climate and weather, international travel and commerce, war and famine, technology and industry, microbial adaptation and change, economic development and land use, development of multiple-resistant bacterial pathogens, emerging issues in blood borne infections, resurgent vector borne diseases. The surveillance and control of emerging and re-emerging diseases.

1. Concept of emerging and re-
emerging diseases
Anthony Z. Dongdem
16/06/2021

2. Course Objective
At the end of this session students should;
• Explain the meaning of emerging and re-emerging infectious diseases
• Describe the factors contributing to the emergence of infectious diseases
• Identify the recent emerging viral and zoonotic infectious diseases
• Identify food and water borne emerging infectious diseases
• Understand the emergence of antibiotic and multi resistance pathogens
• Understand bioterrorism in the emergence of infectious diseases

3. Emerging infectious diseases
• Emerging infectious diseases are ‘new diseases; new problem (new
threats)’
• An emerging disease is one caused by a newly discovered infectious
agent
OR
• A newly identified pathogen, which has emerged and whose
incidence in humans has increased during the last 2 decades and
threating to increase in the near future

4. Re-emerging infectious diseases
• Re-emerging infectious diseases are ‘old disease, new problem (new
threats)’
• A re-emerging infectious disease is one which was previously
controlled but once again has risen to be a significant health problem
• This term also refers to that disease which was formerly confined to
one geographical area, has now spread to other areas

5. Factors contributing to the emergence of
infectious diseases
There are many factors contribute to infectious disease
emergence
These can be classified under;
1. Agent factors
2. Host factors
3. Environmental factors

6. Factors contributing to the emergence of
infectious diseases`-
Agent Factors
• Evolution of pathogenic infectious agents (microbial adaptation &
change)
• Development of resistance to drugs: Wrong prescribing practices
Non-adherence by patients
Counterfeit drugs
Use of anti-infective drugs in animals & plants
• Resistance of vectors to pesticides

7. Factors contributing to the emergence of
infectious diseases
Host Factors
• Human demographic change (inhabiting new areas)
• Human behaviour:
1. Unsafe sexual practices (HIV, Gonorrhoea, Syphilis)
2. Changes in agricultural & food production patterns-
foodborne infectious agents (E. coli)
3. Increased international travel (Influenza)
• Human susceptibility to infection (Immunosuppression)
• Poverty & social inequality

8. Factors contributing to the emergence of
infectious diseases
Environmental factors
• Climate & changing ecosystems:
- Deforestation forces animals into closer human contact- increased
possibility for agents to breach species barrier between animals &
humans
- EL Nino - Triggers natural disasters & related outbreaks of
infectious diseases (Malaria, Cholera)
- Global warming- spread of Malaria, Dengue, Leishmaniasis,
Filariasis

9. Factors contributing to the emergence of
infectious diseases
• Economic development & Land use (urbanization, deforestation)
• Technology & industry (food processing & handling)
• International travel & commerce
• Deterioration in surveillance systems (lack of political will)

10. Factors contributing to the emergence of
infectious diseases
• Breakdown of public health measure (war, unrest, overcrowding):
- Poor populations- major reservoir & source of continued
transmission
- Poverty- Malnutrition- Severe infectious disease cycle
- Lack of funding, Poor prioritization of health funds, Misplaced
in curative rather than preventive infrastructure, failure to
develop adequate health delivery systems

11. Factors contributing to the emergence of
infectious diseases
• Uncontrolled Urbanization & Population Displacement:
- Growth of densely populated cities- substandard housing, unsafe
water, poor sanitation, overcrowding, indoor air pollution (>10%
preventable ill health)
- Problem of refugees & displaced persons
- Diarrhoeal & Intestinal parasitic diseases, ARI

12. Evolution of pathogenic agents
Microbial adaptation and Change
• Microorganisms like all other living things are constantly evolving
• Emergence of antibiotic-resistant bacteria is as a result of
antimicrobials adaptation and the power of natural selection
• As such antibiotic-resistant bacteria and drug-resistant parasites has
become frequent, driven by the wide and sometimes inappropriate
use of antimicrobial drugs in a variety of applications

13. Evolution of pathogenic agents
• Pathogens can also acquire new antibiotic resistance genes from other, often
non-pathogenic, species in the environment selected or perhaps even driven by
the selection pressure of antibiotics
• Many viruses show a high mutation rate and can rapidly evolve to yield new
variants
• A classic example is influenza which possess hemagglutinin(HA) and
neuraminidase (NA)
• ‘Antigenic drift’ usually occur in the influenza viruses when there is a small
change in the HA to produce viruses that are closely related to one another

14. Evolution of pathogenic agents
• This occur with the regular annual epidemics from previously
circulating influenza strain
• An ‘antigenic shift’ may occur when there is an abrupt major change
in HA and NA proteins in influenza that infect humans may
• Drift occurs in all types of influenzas ie A, B, C, while shift occurs only
in influenza A because it infects more that just humans
• The shifts therefore are the common mechanism that results in the
evolution of new variants eg H1N1, H5N1

15. Changes in human demographic
• Human population movements, caused by migration or war, are often
important factors in disease emergence
• In many parts of the world, economic conditions are encouraging the mass
movement of workers from rural areas to cities
• These movement from rural to urban towns allows infections arising in
isolated rural areas to be introduced to towns/cities
• Such infections have the opportunity to spread locally among the
population because of the crowded urban populations and ease of
transportation
• E.g TB because of the high population density setting

16. Behaviour change
• Human behaviour can have important effects on disease
dissemination
• The best known examples are;
- Sexually transmitted diseases such as HIV, gonorrhea, syphilis
- intravenous drug use have contributed to the emergence of
HIV, HBV, HCV infections are now well known.

17. International travel and commerce
• In the past infections were introduced into different geographically locations
through travel, commerce, or war
• The rat that spreads bubonic plague was introduced to Europe through trade
routes
• During the beginning of the 16th and 17th centuries, ships bringing slaves
from West Africa to the New World also brought yellow fever and its
mosquito vector, Aedes aegypti, to the new territories.
• Similarly, smallpox escaped its Old World origins to cause new havoc in the
New World

18. International travel and commerce
• In the 19th century, cholera had similar opportunities to spread from
its probable origin in the Ganges plain to the Middle East and, from
there, to Europe and much of the remaining world
• Each of these infections had once been localized and took advantage of
opportunities to be carried to previously unfamiliar parts of the world
• The opportunities in recent years have become far richer and more
numerous, reflecting the increasing volume, scope, and speed of traffic in
an increasingly mobile world

19. International travel and commerce
• E.gs
• the rats that carry hantaviruses has spread worldwide, Aedes
albopictus (Asian tiger mosquito) that causes equine
encephalomyelitis spread, cholera from Bangladesh to all parts of the
world
• another mosquito-borne disease, malaria, is one of the most
frequently imported diseases in non-endemic-disease areas, and
cases of airport malaria are occasionally identified

20. Technology and Industry
• Modern food production makes use of products of biological origin to
yield increase production at a reduced costs
• These process may increase the chances of accidental contamination of
the products
• The problem is further compounded by globalization, allowing the
opportunity to introduce agents from far away
• A pathogen present in some of the raw material may find its way into a
large batch of final product, as happened with the contamination of
hamburger meat by E. coli strains causing haemolytic uremic syndrome

21. Technology and Industry
• Bovine spongiform encephalopathy (BSE) also referred to ‘mad cow
disease’ which emerged in Britain within the last few years is believed
to be due to misfolded protein known as prion
• The cattle are believed to have being infected from been fed with
meat and bone meal from remains of cattle infected with the disease
or from scrapie-infected sheep products
• Not forgetting the transmission of diseases such as HIV, Hep B and C
etc in the past that also helped to spread infections

22. Technology and Industry
• Some outbreaks in Africa have been attributed to secondary
infections acquired at the hospitals
• e.g
- through contaminated hypodermic apparatus, and from some to
the health care staff by contact.
- Transmission of Lassa fever to health care workers has also been
documented
• On the positive side, advances in diagnostic technology can also lead
to new recognition of agents that are already widespread.

23. Ecological changes
• Ecological factors usually precipitate emergence of infectious diseases
by placing people in contact with a natural reservoir or host for an
infection (often a zoonotic or arthropod-borne infection)
• This is by either increasing proximity or by changing conditions so as
to favour an increased population of the microbe or its natural host
• This can be observed during the creation of a hydro dam which often
increase the proliferation of vectors of diseases

24. Ecological changes
• The emergence of Lyme disease in the United States and Europe was
probably due largely to reforestation which increased the population
of deer and the deer tick, the vector of Lyme disease
• This brought vectors closed to human settlements with the
consequence of disease spread

25. Agricultural development
• Agricultural development is one of the most common ways in which people
alter and interpose themselves into the environment
• Hantaan virus which has been responsible for Korean hemorrhagic fever
for centuries has its natural host in field mouse Apodemus agrarius.
• The rodent flourishes in rice fields and people contract the disease during
the rice harvest from contact with infected rodents.
• Junin virus, the cause of Argentine hemorrhagic fever, is an unrelated virus
with a history remarkably similar to that of Hantaan virus

26. Agricultural development
• Conversion of grassland to maize cultivation favoured a rodent that was the
natural host for this virus, and human cases increased in proportion with
expansion of maize agriculture
• Water is also frequently associated with disease emergence
• Infections transmitted by mosquitoes or other arthropods, which include
some of the most serious and widespread diseases
• Are often stimulated by expansion of standing water, simply because many
of the mosquito vectors breed in water

27. Breakdown of Public Health Measures
• The pathogens themselves often still remain, albeit in reduced numbers, in
reservoir hosts or in the environment, or in small pockets of infection
• They take advantage of the opportunity to re-emerge if there are
breakdowns in preventive measures
• Cholera cases which were once decreasing are on the increase in some parts
of Africa
• A recent increase in cases of cholera in South America may have been
abetted by recent reductions in chlorine levels used to treat water supplies

28. HUMAN
ANIMALS
ENVIRONMENT
VECTORS
Population
Growth
Mega-cities
Migration
Exploitation
Pollution
Climate change
Vector
proliferation
Vector
resistance
Transmission
Antibiotics
Intensive farming
Food
production

29. Emerging Zoonoses: Human-animal
interface
Dr. KANUPRIYA CHATURVEDI
Marburg virus
Hantavirus Pulmonary Syndrome
Ebola virus
Borrelia burgdorferi: Lyme Deer tick (Ixodes
scapularis)
Mostomys rodent: Lassa fever
Avian influenza virus Bats: Nipah virus

30. Recent emerging viral infections
SARs
• Severe acute respiratory syndrome (SARS) is a viral respiratory disease
caused by a SARS-associated coronavirus
• It was first identified at the end of February 2003 during an outbreak
that emerged in China and spread to other countries.
• It resulted in 8439 cases with 812 deaths in 30 countries
• SARS is an airborne virus and can spread through small droplets of
saliva in a similar way to the cold and influenza.

31. Recent emerging viral infections
• It was the first severe and readily transmissible new disease to emerge in
the 21st century and showed a clear capacity to spread along the routes of
international air travel.
• SARS can also be spread indirectly via surfaces that have been touched by
someone who is infected with the virus.
• Fever, dry cough, headache, muscle aches and difficulty breathing are
symptoms
• Diagnosis involve clinical and laboratory confirmation

32. Recent emerging viral infections
Swine flu
• H1N1 is commonly referred to as the “swine flu” due to its similarities with
the flu virus that affects pigs but is spread from person to person
• Caused by A(H1N1) in 2009 and designated as influenza A(H1N1)pdm09
virus
• An estimated 105,700-395,600 people died due to respiratory
complications attributed to H1N1 influenza during the first 12 months of
the virus’s outbreak
• Over 80% of the deaths occurred among people less than 65 years

33. Recent emerging viral infections
• It has become a regular human flu
• There is vaccine available to protect against the disease
• It is contagious and can be contracted through coughing, sneezing or
even talking to someone carrying it.
• It can also be contracted through mouth or nose contact with
something contaminated

34. Recent emerging viral infections
• The H1N1 influenza virus causes moderate to severe respiratory
infections. Symptoms include fever, sore throat, cough, headache,
chills and fatigue.
• Severe cases include bacterial pneumonia bronchitis, sinus infections
and an increase in underlying conditions
• Diagnosis involve clinical and laboratory confirmation

35. Recent emerging viral infections
Highly pathogenic Avian influenza (H5N1)
• Since Nov 2003, avian influenza H5N1 in birds affected 60 countries
across Asia, Europe, Middle-East &Africa
• >220 million birds killed by this virus or culled to prevent further
spread
• Majority of human H5N1 infection due to direct contact with birds
infected with virus
• It can also be passed from person to person.

36. Recent emerging viral infections
• Symptoms begin within two to eight days with common flu. Cough,
fever, sore throat, muscle aches, headache and shortness of breath
may occur.
• The disease can carry a high mortality in humans.
• Diagnosis involve clinical and laboratory confirmation

37. Recent emerging viral infections
EBOLA
• Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a
rare but severe, often fatal illness in humans.
• EVD first appeared in 1976 in 2 simultaneous outbreaks, one in what is now
Nzara, South Sudan, and the other in Yambuku, DRC.
• The latter occurred in a village near the Ebola River, from which the disease
takes its name.
• The virus is transmitted to people from wild animals and spreads in the
human population through human-to-human transmission. Through;

38. Recent emerging viral infections
- Blood or body fluids of a person who is sick with or has died from
Ebola
- Objects that have been contaminated with body fluids (like blood, feces,
vomit) from a person sick with Ebola or the body of a person who died from
Ebola
• Initial symptoms include fever, headache, muscles pain and chills but
later patients may experience internal bleeding resulting in vomiting or
coughing blood
• The average EVD case fatality rate is around 50%. Case fatality rates have
varied from 25% to 90% in past outbreaks.

39. Recent emerging viral infections
• The largest outbreak occurred between 2014–2016 in West Africa
• A vaccines to protect against Ebola have been developed
• Diagnosis of the disease involve clinical and laboratory confirmation

40. Recent emerging viral infections
Zika
• Zika virus was first discovered in a monkey in the Zika Forest of
Uganda in 1947.
• Zika virus is primarily transmitted by the bite of an infected mosquito
from the Aedes genus, mainly Aedes aegypti, in tropical and
subtropical regions.
• Zika virus is also transmitted from mother to fetus during pregnancy,
through sexual contact, transfusion of blood and blood products, and
organ transplantation.

41. Recent emerging viral infections
• In October 2015, Brazil reported an association between Zika virus
infection and microcephaly. Outbreaks and evidence of transmission soon
appeared throughout the Americas, Africa, and other regions of the world.
• To date, a total of 86 countries and territories have reported evidence of
mosquito-transmitted Zika infection.
• No vaccine is yet available for the prevention or treatment of Zika virus
infection.
• Diagnosis involve clinical with laboratory confirmation

42. Recent emerging viral infections
COVID 19
• Coronavirus disease (COVID-19) is an infectious disease caused by a
newly discovered coronavirus.
• It was first reported in China(Wuhan) November 17, 2019, in the
Hubei Province, but went unrecognized.
• Most people who fall sick with COVID-19 will experience mild to
moderate symptoms and recover without special treatment.

43. Recent emerging viral infections
• Older people, and those with underlying medical problems like
cardiovascular disease, diabetes, chronic respiratory disease, and
cancer are more likely to develop serious illness
• According to the World Health Organization (WHO), over 3 million
COVID-19 deaths occurred worldwide by the end April 2021
• The virus that causes COVID-19 is mainly transmitted through
droplets generated when an infected person coughs, sneezes, or
exhales. These droplets are too heavy to hang in the air, and quickly
fall on floors or surfaces.

44. Recent emerging viral infections
• You can be infected by breathing in the virus if you are within close
proximity of someone who has COVID-19, or by touching a
contaminated surface and then your eyes, nose or mouth.
• Diagnosis involve clinical and laboratory confirmation
• Vaccines are available to protect against the disease

45. Emerging food borne & water borne diseases
• Accounts for 20 million cases in the world annually
• Incidence is increasing
• Half of all known food borne pathogens discovered during the past 25
years
• Most common associated organisms are: Enterohemorrhagic
Escherichia coli (haemolytic uremic syndrome), Vibrio cholerae
(cholera), Campylobacter sp. (campylobacteriosis)

46. Examples of re-emerging infectious diseases
• Diphtheria- Early 1990s epidemic in Eastern Europe (1980- 1% cases;
1994- 90% cases)
• Cholera- 100% increase worldwide in 1998 (new strain Eltor, 0139)
• Human Plague- India (1994) after 15-30 years absence.
• Dengue/ Dengue Hemorrhagic Fever- Over past 40 years, 20-fold
increase to nearly 0.5 million (between1990-98)

47. Antibiotic resistance
• Emerge in environment due to inappropriate use of antibiotic
• WHO estimates that 10 million people are dying of infectious diseases
related to antibiotic resistance.
• Proper antibiotic guidelines needed to prevent the drug resistance

48. Multi-resistant pathogens
• Staphylococcus aureus is the most frequently identified drug-resistant
pathogen
• Singhal et al (2007) reported ciprofloxacin-resistant meningococci in an
outbreak in Delhi.
• Resistance of Salmonella typhi and S. paratyphi to chloramphenicol,
ampicillin and cotrimoxazole is widespread.
• Antimicrobial resistance in Shigella: resistance to azithromycin, ceftriaxone
and ciprofloxacin on the increase
• Methicillin/oxacillin-resistant Staphylococcus aureus (MRSA)

49. Multi-resistant pathogens
• Vancomycin-resistant enterococci (VRE)
• Extended-spectrum beta-lactamases (which are resistant to
cephalosporins & monobactams) (ESBLs)
• Penicillin-resistant Streptococcus pneumoniae (PRSP)
• Multi-drug resistant tuberculosis (MDR-TB)

50. Multi-resistant pathogens
• CRKP- Carbapenem Resistant Klebsiella Pneumoniae
• S. typhimurium - DT104 (resistant to five antibiotics: ampicillin,
chloramphenicol, streptomycin, sufonamides and tetracycline)

51. Examples of recent emerging diseases
Dr. KANUPRIYA CHATURVEDI
Source: NATURE; Vol 430; July 2004;
www.nature.com/nature

52. Bioterrorism
• Possible deliberate release of infectious agents by dissident individuals or
terrorist groups
• Biological agents are attractive instruments of terror- easy to produce,
mass casualties, difficult to detect, widespread panic & civil disruption
• Highest potential- B. anthracis, C. botulinum toxin, Y. pestis, Variola virus,
Viral haemorrhagic fever viruses
• Likeliest route- aerosol dissemination

53. Thank You