This document defines emerging and re-emerging infections. Emerging infections are those whose incidence in humans has increased in the past two decades or are expected to increase. Re-emerging infections were previously clinically silent but have reappeared. Major causes of emerging infections include changes in human behavior, environments, travel, and antimicrobial resistance in known pathogens. The document lists many bacterial, viral, fungal and parasitic pathogens that have emerged since 1972. It describes different modes of transmission including waterborne, foodborne, respiratory, zoonotic, vector-borne and nosocomial.

1. EMERGING & RE-
EMERGING INFECTIONS
MI 8.4
Dr V S Vatkar
Associate Professor
Department of Microbiology
D Y Patil Medical College, Kolhapur

2. DEFINITION
EMERGING INFECTIONS: Infectious
diseases whose incidence in humans has increased in
the past two decades or threatens to increase in the
near future
 Emerging pathogens are those that have appeared in a
human population for the first time, or have occurred
previously but are increasing in incidence or expanding
into areas where they have not previously been
reported, usually over the last 20 years. OR increase
incidence of epidemic outbreak e.g. Cryptosporidiosis,
E.coli O157:H7, Hantavirus, HIV, SARS, MRSA etc.

3. New infection resulting from changes or
evolution of existing organism
Known infection spreading to new
geographic area or population
Previously unrecognized infections
appearing in areas undergoing ecologic
transformation

4. RE-EMERIGING INFECTIONS:
definition
 Old infections which were clinically silent or reduced in
incidence, have again re-emerge in the community
 Antimicrobial resistance in known agents or
breakdown in public health measures
 Chikungunya virus re-emerging after 2005
 MDR-TB
 XDR-TB
 MRSA
 VRSA
 ESBL

5. In 2001, a review of the scientific literature
identified
1415 species of infectious organisms known to
be pathogenic to humans, including
217 viruses and prions,
538 bacteria and rickettsiae,
307 fungi,
66 protozoa and
287 helminths.
Of these, 61% were zoonotic and 12% were
associated with diseases considered to be
emerging.

6. Major etiological agents of
infectious diseases identified
since 1972
Year Agent Disease
1972 Small round structured viruses
Diarrhea
1973 Rotaviruses Infantile diarrhea
1975 Astro viruses Diarrhea
1975 Parvovirus B19 Aplastic crisis in
chronic hemolytic anaemia
1976 Cryptosporidium parvum ,Acute
enterocolitis

7. 1977 Ebola virus Ebola haemorrhagic
fever
1977 Legionella pneumophila
Legionnaires’ disease
1977 Hantaan virus Haemorrhagic fever
with renal syndrome
1977 Campylobacter spp. Diarrhoea
1980 Human T-cell lymphotropic virus-
1(HTLV-1) Adult T-cell leukaemia/ HTLV-1
associated myelopathy
1982 HTLV-2 Hairy T-cell leukaemia

8. 1982 Borrelia burgdorferi Lyme disease,
1982 Escherichia coli O157:H7
Haemorrhagic colitis; haemolytic
uremic syndrome
 1983 HIV-1, HIV-2 Acquired
immunodeficiency syndrome
 1983 Helicobacter pylori gastritis, gastric
ulcers, increased risk of gastric cancer
1988 Human herpesvirus-6 Exanthema
subitum, Hepatitis E V
1989 Ehrlichia spp. Human ehrlichiosis

9.  1989 Hepatitis C virus Parenterally transmitted
non-A, non-B hepatitis
 1990 Human herpesvirus-7 Exanthema
subitum
 1991 Hepatitis F virus Severe non-A, non-B
hepatitis
 1992 Vibrio cholerae O139:H7 New strain
associated with epidemic cholera
 1992 Bartonella henselae CAT-scratch disease,
bacillary angiomatosis

10.  1993 Sin nombre virus Hantavirus
pulmonary syndrome
 1993 Hepatitis G virus Non A-C hepatitis
 1994 Sabia virus Brazilian hemorrhagic
fever
 1994 Human herpesvirus-8 Kaposi’s
sarcoma
 1995 Hendravirus Castleman’s disease
 1996 Prion (BSE) Meningitis, encephalitis
 1997 Influenza A virus New variant
Creutzfeldt-Jakob disease

11.  1997 Enterovirus 71 Epidemic
encephalitis
 1999 Nipah virus Meningitis, encephalitis
 2002 SARS corona virus
 2003 Influenza A (H51N1)
 2004 Plasmodium knowlesi
 2009 Influenza A (H1N1)
 2012 Novel Corona V (middle-east respiratory
syndrome corona v)

12.  2013 sever fever with thrombocytopenia
syndrome virus
 2019-20 COVID-19 pandemic due to SARS
corona virus 2

13. WHY DO PATHOGENS
EMERGE? Reasons.
New environments : new technologies like
dams & irrigation systems, leads to spread of
malaria, schistosomiasis, J E, AC systems:
legionella inf. etc.
Scientific advances: inappropriate & excessive
use of antibiotics & antiparasitic drugs.
 ■ Improved methods of detection and analysis
 ■ Inappropriate use of new generation insecticides.

14.  Changes in human behavior and
vulnerability: Human circulation and the
accessibility and rapidity of transport
worldwide.
 ■ Deliberate and accidental release of
pathogens to water.
* Individual’s level of nutrition and fitness,
stress, excessive exposure to ultraviolet
irradiation, and pregnancy.

15.  New techniques:
 Filtration of water, agricultural and wastewater
management practices, may be anticipated and
subsequently controlled by implementing
appropriate resource protection and management
strategies.

16. Other factors
Demographic : increase size of high risk
population.
Socio-economic factors: may be
anticipated, but the outcomes are
unpredictable and appropriate control
measures difficult to implement.

17. List of emerging pathogens
Human infection: caused by
bacteria, viruses, fungi & parasites.
Sources of these infections are
different like water borne, inhalation,
ingestion etc.
Plant pathogens: may cause inf in
humans.
Animal pathogens: zoonotic diseases.

18. Bacterial infections
EHEC, VTEC, O 157: H 7 E.coli
Legionella pneumophila
Burkholderia / Stenotrophomonas
H.pylori
Chlamydia spp.
Borrelia burgdorferi : Lyme ds
Streptococcus pyogenes
Mycobacteria spp

19. Staphylococcus aureus & staph epidermidis
: nosocomial inf.
Enterococci
Bordetella pertussis
Tropheryma whippelii
Compylobacter jejuni
Mycoplasma
Ehrlichia spp.

20. viruses
West-Nile virus
Arboviruses
causing J E,
Yellow fever
Norwalk virus
HIV
Rota V
Avian flue
Nipah V
Influenza V
HTLV
Ebola V
Hanta V
Corona V

21. Fungi
black moulds found in environment
(immunity of person decreases inf occurs):
a) skin inf (warts & cauliflower like
lesions). Redness, swelling, discharge,
pain at the inf site. b) Pneumonia
most common inf. c) Sinusitis
MOI: inhalation of spores
Treatment: antifungal agents, surgical
excision
No vaccine available.
Zygomycetes (eg, Mucor and Rhizopus ),
Fusarium, Trichosporon,
Pseudallescheria, and Scedosporium.

22. Parasites:
cryptosporidium parvum
Isospora belli
Giardia
Malarial inf

23. TRANSMISSION OF
INFECTION (diff modes)
Water borne infections: include
 Cryptosporidium, Giardia
 Legionella, Escherichia coli O157 (E. coli O157),
Cholera O139,
 rotavirus, hepatitis E virus
 norovirus (formerly Norwalk virus).
 Helicobacter pylori (H. pylori)

24. Coronavirus responsible for
Severe Acute Respiratory Syndrome
(SARS) : transmitted through ‘droplets’.
Mycobacterium Avium Complex (MAC):
leading cause of death in HIV pts. Drinking
water plays an imp role in the spread of inf.

25. Cyclospora cayetanensis: food borne
outbreaks in Dec 2000, southwest
Germany, oocysts transmit thr’ local
contact & thr’ water.
Schistosomiasis : S.mansoni
Severe illness due to dermal contact with
toxic cyanobacteria has been reported
from tropical marine bathing sites

26. Zoonotic infections :
Vector borne:
A) Mosquito : J E, dengue, Yellow fever,
chikungunya, West-Nile fever
(Arboviruses).
B) Tick : KFD, Colorado tick fever, Russian
spring summer encephalitis, Rickettsial
diseases: Tick typhus.

27. C) Rat flea : Y.pestis, Endemic typhus
D) Rat : Borrelia burgdorferi, Leptospira
inf. Lassa fever V.
Nosocomial infection:
 MRSA, Multidrug resistant E.coli,
P.aeruginosa, Clostridium difficile, Serratia
spp., Enterococcus infections.

28. Inhalation:
Fungal infections: inhalation of spores
(black moulds, opportunistic fungi etc.)
Influenza virus: Avian flu strain: higher
mortality. H5N1 strain outbreak in Hong-
Kong ,2008 (in birds).
COVID-19

29. Food-related diseases include
hepatitis caused by the hepatitis E virus,
 intestinal spirochetosis caused by
Brachyspira pilosicoli, gnathostomiasis
caused by nematodes and anisakidosis caused
by fish nematodes.
non-gastric Helicobacter spp., Enterobacter
sakazakii, non-jejuni/coli species of
Campylobacter, and non-O157 Shiga toxin-
producing Escherichia coli. , Y.enterocolitica,
M.paratuberculosis (chrohn’s ds),