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The Environment and Emerging Biological Hazards In The Pacific Basin

David KohMBBS (S’pore), MSc (Occup Med), PhD (Birm), FFOM (Lond), FFOM (Ire), FFPH (UK), FAMS

Professor and HeadDepartment of Community, Occupational

and Family Medicine Yong Loo Lin School of Medicine

Seminar on Public Health & The Environment In the Pacific Basin

Singapore – Auckland, 22 Apr 2006

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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

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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

4Source: WHO, 2003

SARS 2002-2003

Emerging and re-emerging biological hazards in the world

?

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Hendra Virus Outbreaks (Australia)

Hendra VirusFamily : ParamyxoviridaeGenus : 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 viruses in Queensland piggeries.  Australian Veterinary Journal.  June; 79 (6): 424-426.

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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.

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Nipah virus outbreaks (Malaysia/Singapore 1998-1999)

Sep 1998 – Apr 1999 Malaysia (265 cases, 105 died) Almost all had exposure to pigsIncubation: 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.

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Re-emergence in Bangladesh (2004)

Apr-May 2001, Jan 2003 outbreaks in Bangladesh – mainly children74% 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

9Probable cases of SARS worldwide, 7 August 2003. Source: WHO

Cumulative Total : 8,422 cases and 916 deaths, reported from 29 countries

SARS

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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

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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

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Most likely scenarios :

1 Original or new animal reservoir

2 Undetected transmission in humans (? Seasonal)

3 Persistent infection in humans

4 Laboratory accidents

Will SARS Re-emerge ?

4 cases in China, Dec 03-Jan 04

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Influenza A Viruses

Source: Nicholson, Wood and Zambon. Lancet 2003; 362: 1733-45.

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

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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

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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

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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 Other Animals

http://www.fao.org/ag/againfo/subjects/en/health/diseases-cards/avian_cats.html

H5N1 in CATS – leopards, tigers, domestic cats

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Total: 194 cases109 deaths(56%)

http://gamapserver.who.int/mapLibrary/app/searchResults.aspx

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Influenza Pandemics in the Last Century

1918-19 Spanish Influenza H1 N1 30 million deaths

39 years later . . .

1957-58 Asian Influenza H2 N2 1 million deaths

11 years later . . .

1968-69 Hong Kong Influenza H3 N2 800,000 deaths

37 years later . . .

2006 ? ? ? Bird flu or something else ? ? ? millions

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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 imminent