Download Prof David Koh, Head of the Department of Community

Seminar on Public Health & The Environment In the Pacific Basin
Singapore – Auckland, 22 Apr 2006
The Environment and Emerging
Biological Hazards In The Pacific Basin
David Koh
MBBS (S’pore), MSc (Occup Med), PhD (Birm), FFOM (Lond), FFOM (Ire), FFPH (UK), FAMS
Professor and Head
Department of Community, Occupational
and Family Medicine
Yong Loo Lin School of Medicine
1
Emerging Infectious Diseases
Definition
Diseases in flux, either rising in
incidence, expanding in host or
geographic range, or changing in
pathogenicity, virulence, or some
other factor
2
Why do these diseases emerge ?
Emergence almost always driven by :
•Large-scale environmental change
e.g. deforestation, agricultural
encroachment, urban sprawl
* Change in human population structure
e.g. increased density linked to urbanization
* Change in human behavior
e.g. increasing drug use, changes in medical
practice, agricultural intensification,
international trade
3
Emerging and re-emerging biological
hazards in the world
?
SARS
2002-2003
Source: WHO, 2003
4
Hendra Virus Outbreaks (Australia)
Hendra Virus
Family : Paramyxoviridae
Genus : Henipavirus (Nipah and Hendra viruses)
1994-95 Queensland outbreak (3 cases, 2 deaths)
1999 outbreak
- close contact with infected horses
Clinical features of Hendra virus infection
– severe flu-like symptoms, subsequent encephalitis,
respiratory and renal failure
Murray K, Selleck P, Hooper P. A morbillivirus that caused fatal disease in horses and humans.
Science 1995; 268:947.
Black, P., et al. 2001. Serological examination for evidence of infection with Hendra and Nipah 5
viruses in Queensland piggeries. Australian Veterinary Journal. June; 79 (6): 424-426.
Nipah Virus
Family : Paramyxoviridae
Genus : Henipavirus
(Nipah and Hendra viruses)
Enveloped, Single stranded,
non-segmented RNA genome
Virus named after village near Kuala
Lumpur from where it was first isolated
Sep 1998- Apr 1999
- 265 cases, 105 died
Chua et al. Nipah virus: a recently emergent deadly paramyxovirus. Science 2000;288(5470):1432-5.
6
Nipah virus outbreaks (Malaysia/Singapore 1998-1999)
Sep 1998 – Apr 1999
Malaysia (265 cases, 105 died)
Almost all had exposure to pigs
Incubation: 4 -18 days, May be mild / inapparent infection
In symptomatic cases,
“influenza like symptoms” with high fever, myalgia
encephalitis, convulsions and coma (40% mortality)
Singapore (11 cases, 1 died)
- contact with infected pigs
Goh et al. Clinical features of Nipah virus encephalitis among
pig farmers in Malaysia. N Engl J Med 2000; 27;342(17):1229-35.
7
Re-emergence in Bangladesh (2004)
Apr-May 2001, Jan 2003
outbreaks in Bangladesh – mainly children
74% mortality
Jan- Apr 2004 outbreak - killed 35 people
- children who had direct contact
with bat-contaminated fruit
Choi C. Nipah’s return. Scientific American 2004
Sep;291(3):21A, 22.
Hsu VP, Hossain MJ, Parashar UD, Ali MM, Ksiazek TG, Kuzmin I, et al. Nipah virus
encephalitis reemergence, Bangladesh. Emerg Infect Dis [serial on the Internet]. 2004 Dec
[date cited]. Available from http://www.cdc.gov/ncidod/EID/vol10no12/04-0701.htm
8
SARS
Probable cases of SARS worldwide, 7 August 2003. Source: WHO
Cumulative Total : 8,422 cases and 916 deaths, reported from 29 countries
9
Early cases of SARS
More than 1/3 of cases with dates
of onset before 1 Feb. 2003 were
persons who handled, killed or sold
food animals, or those who prepare
or serve food
10
SARS-CoV Animal and Environmental Reservoirs
Domestic animals
Cats, dogs (+ ve in oropharyngeal
and rectal swabs)
Others
Rodents (rats)
Wildlife
Masked palm civet cat
Racoon dog
11
Will SARS Re-emerge ?
Most likely scenarios :
1 Original or new animal reservoir
2 Undetected transmission
in humans (? Seasonal)
4 cases in
China, Dec
03-Jan 04
3 Persistent infection in humans
4 Laboratory accidents
12
Influenza A Viruses
Orthomyxovirus - with 8 segmented ssRNA genome
Subtypes based on basis of two surface antigens:
- Hemagglutinin (H) (15)
- Neuraminidase (N) (9)
H1N1, H3N2 and H1N2 affect humans and are globally
circulated
H5N1 - causes avian influenza
Source:
Nicholson, Wood and Zambon.
Lancet 2003; 362: 1733-45.
13
Why the Concern about H5N1
H5N1 strain mutates frequently
H5N1 has the capacity to jump the
species barrier to cause disease in
humans (documented in 1997, 2003-06)
H5N1 infection in humans has a high fatality rate
Genetic mutation in the last few years show increasing
H5N1 virulence and capacity to infect mammals
? Emergence of a new subtype of virus that can infect
humans and be transmitted to other humans
14
Why Asia ?
* Densely packed people living closely with
birds / animals
* Farming and marketing habits
- ducks, chickens, pigs kept together with family
- shopping at live animal markets
* Major bird migratory pathways
- from Siberia across Asia
15
H5N1 in Other Animals
Haiyan L. I. & Chin J.
Chinese J. Prev. Vet. Med., 26. 1 - 6 (Jan 2004)
H5N1 virus found in 2003 in pigs in southeast China
Haiyan L. I. & Chin J.
Chinese J. Prev. Vet. Med., 24. 304 - 309 (May 2004)
Reported similar results from pigs tested elsewhere in 2001 and 2003
H5N1 in CATS
– leopards, tigers, domestic cats
http://www.fao.org/ag/againfo/subjects/en/health/diseases-cards/avian_cats.html
16
http://gamapserver.who.int/mapLibrary/app/searchResults.aspx
Total: 194 cases
109 deaths(56%)
17
Influenza Pandemics in the Last Century
1918-19
Spanish Influenza
H1 N1
30 million deaths
H2 N2
1 million deaths
H3 N2
800,000 deaths
39 years later . . .
1957-58
Asian Influenza
11 years later . . .
1968-69
Hong Kong Influenza
37 years later . . .
2006
? ? ? Bird flu or something else
? ? ? millions
18
Summary
Several infectious diseases recently
emerged in the Pacific basin
Emergence due to changes in the
environment / people
Illnesses are severe with mortality rates
of 10%-75%
These outbreaks recur – we should be
alert & prepared
A worldwide pandemic may be imminent19