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Yellow fever:threat to Asia
Jack Woodall PhD
Institute of Medical Biochemistry
Federal University of Rio de Janeiro
Brazil
ASIA
Jack Woodall PhD
Institute of Medical Biochemistry
Federal University of Rio de Janeiro
Brazil
(retired)
Imported Yellow feverAmericas
• USA1999 (California ex Venezuela) fatal ϯ• Unvaccinated tourist• Urban YF vector mosquito Aedes aegypti does NOT occur
in California
USA 2002 (Texas ex Brazil) fatal ϯ• Unvaccinated tourist fishing on Amazon• Urban YF vector mosquito Aedes aegypti occurs
in Texas…• But case was hospitalized in USA in March, before
mosquito season, therefore no epidemic possible
• USA1999 (California ex Venezuela) fatal ϯ• Unvaccinated tourist• Urban YF vector mosquito Aedes aegypti does NOT occur
in California
USA 2002 (Texas ex Brazil) fatal ϯ• Unvaccinated tourist fishing on Amazon• Urban YF vector mosquito Aedes aegypti occurs
in Texas…• But case was hospitalized in USA in March, before
mosquito season, therefore no epidemic possible
Imported Yellow fever Europe
Germany 1999 (ex Côte d'Ivoire) fatal ϯ
Netherlands 2000 (ex Suriname) survived
Belgium 2001 (ex Gambia) fatal ϯ• Unvaccinated tourists• Urban YF vector mosquito Aedes aegypti occurs
only in Spain, Portugal, & southernmost parts of Italy & Greece
• So, imported cases of YF into these more northern parts of Europe did not result in epidemics.
If USA & Europe, why not Asia?
All of tropical Asia is infested with the urban yellow fever mosquito,
Aedes aegypti
Aedes albopictus problem
“We conclude that the Houston (USA) strain of Ae. albopictus is a competent vector of yellow fever virus and can serve as bridging vector between the jungle yellow fever cycle and the urban cycle in New World ecosystems.”
(Miller BR, Mitchell CJ, Ballinger ME. 1989)
[It could therefore also transmit YF in Asia]
Map 3. Ae. albopictus: global spread
Source: Landcare Research, Keys to the Mosquitoes of New Zealand (2004)
Yellow fever 1 Jan. 2012 - 28 Feb. 2013
AFRICA• Cameroon• Chad *• Congo Republic• Ghana• Nigeria *• Senegal• Sierra Leone• Sudan *• Uganda
AMERICAS• Bolivia *• Peru *
* 2013
Yellow fever in capital citieswith international airports
AFRICA, 2010
Abidjan, Côte d’Ivoire
SOUTH AMERICA, 2008
Asuncion, Paraguay
Travel times (including connections)
Nearest points:
• Abidjan – Pakistan
• Total airport airport 23hrs
Furthest points:
• Asuncion – Jakarta
• Total airport airport 35hrs
Why hasn’t YF broken out in Asia yet?
1. Cross-immunity theory • the Asian population is protected by cross-
immunity, because so many have had dengue?
• BUT neither dengue nor Japanese encephalitis patients produce neutralising antibodies to YF
– Ref: Makino Y et al. Studies on serological cross-reaction in sequential flavivirus infections.
Microbiol Immunol. 1994;38(12):951-5
Why hasn’t YF broken out in Asia yet?
2. Vector competence theory• Asian Aedes aegypti mosquitoes are not as
competent as the vectors of YF in Africa & South America?
• BUT lab tests show this does not matter
- Ref: Miller BR, Monath TP, Tabachnick WJ, Ezike VI.
Trop Med Parasitol. 1989 Dec;40(4):396-9. Epidemic yellow fever caused by an incompetent mosquito vector.
Diagnosis & Surveillance situation
• Nobody in Asia is expecting to see a case of YF– therefore a case of high fever with jaundicejaundice and
hemorrhagichemorrhagic symptoms will be put down to DHF, hepatitis or something else, but NOT YF
– no lab test for YF will be requested
• Probably only the national reference lab will have reagents – preferably the rapid PCR test for YF
• YF is probably not a reportable disease – although it should be because of the new IHR
Vaccine situation (1)
• Stocks: existing world stocks are INSUFFICIENT to counter a major epidemic in
Asia
• Supply: production CANNOT be ramped up fast enough to provide
protection to all of Asia
• Distribution: vaccine requires a cold chain. Cold chains exist in Asian countries BUT are only adequate to handle enough
vaccine for the childhood cohort
Vaccine situation (2)
• Application: a crash program of mass training and mobilization of vaccinators is beyond the capacity of many Asian countries
• Adverse effects: one or two deaths due to the vaccine (inevitable during mass campaigns) are sufficient to shut down a vaccination program
• Cultural resistance: some Asian countries may resist vaccination (as happened recently with polio vaccination in West Africa).
Vector control situation
Existing vector control programs in Asia are failing to control dengue
• Temporary use of DDT could help (legal in India)
• BUT a crash program of training & deployment of spray workers would take time
• AND experience has shown that householders find spray obnoxious and close up their houses when sprayers pass -- protecting the mosquitoes inside!
Health care situation
There is NO specific therapy for YF
In hospitals:• Stocks of antiviral drugs will soon be exhausted
In rural areas:• Stocks of intravenous fluids will soon be
exhausted
[Fortunately, YF is not transmitted by fomites, because stocks of disposable syringes, needles, etc.
will run out – and they will be re-used, spreading hepatitis & HIV]
Containment situation
• Populace will flee– when plague broke out in Surat, India in 1994, 400 000 people (1/5 of the population) fled the city
• Some reached New Delhi & even Pakistan – potentially spreading the infection
Population (x1000) at risk for YF in Asia*- more than 2.5 billion
Bangladesh 150 494 Malaysia 28 859
Bhutan 783 Nepal 30 486
Cambodia 14 305 Pakistan
Papua N.G.
176 745
7 014
China at risk**
Macau SAR
Hong Kong SAR
336 891
550
7 122
Philippines
Singapore
Sri Lanka
94 852
5 188
21 045
India 1 241 492 Thailand 69 519
Indonesia 242 326 Viet Nam 88 792
Laos 6 288 (Yemen 24 800)
Myanmar 48 337 TOTAL 2 595 056
*UNDP Population estimates (2011) rounded **very rough estimate (approx. 25% of pop.)
CONCLUSIONWHY hasn’t YF broken out in Asia yet?
We don’t know!• BUT because of fast airline through routes,
the risk is higher than it has ever been
• IF YF does break out, there will be • insufficient vaccine and
• inadequate vector control
With up to 2.6 billion people exposed
• And a CFR of up to 50%,
MILLIONS WOULD DIE!MILLIONS WOULD DIE!
YF contingency plan?
• We have had over 5 years to worry about
avian flu
• There is now a plethora of plans in many countries to combat its spread
• We have had decades to think about YF invading Asia
• Is there even
ONE
contingency plan for that?
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