D1983.PDF

Rev. sci. tech. Off. int. Epiz., 2001, 20 (2), 605-613
Traceback systems used during recent
epizootics in Asia
Y. Ozawa (1), B.L. Ong (2) & S.H. An (3)
(1) Office International des Epizooties Representation for Asia and the Pacific, East 311, Shin Aoyama Building,
1-1-1 Minami-Aoyama, Minato-ku, Tokyo 107-0062, Japan
(2) Department of Veterinary Services, 8th Floor Block A, Exchange Square, Off Jalan Semantan, Damansara
Heights, Kuala Lumpur, Malaysia
(3) National Veterinary Research and Quarantine Service, 480 Anyang-6-dong, Manan-gu, Anyang-City,
Republic of Korea
Summary
Traceback systems in most countries of Asia are not well developed, as indicated
by responses to a questionnaire by veterinary officials in thirteen countries.
Marking of animals for traceback is practised only in a limited number of countries
in specific areas or zones and for specific purposes only.
In Malaysia, traceback has been undertaken by marking farm code tattoos on pigs.
This enables the identification of the farm of origin of pigs found to be infected by
Nipah virus in sero-surveillance programmes.
The origin of the foot and mouth disease (FMD) virus that surfaced in the Republic
of Korea in March 2000 was investigated through several epidemiological studies
of suspected sources of contamination such as imported hay, yellow sand, milk
collection trucks and feed delivery trucks. None of these studies gave results that
indicated the origin of the FMD virus. The origin of the FMD virus that was
recorded in Japan in March 2000 was also investigated in epidemiological studies;
in this case, imported wheat straw was incriminated as the most likely source of
infection. Comparative studies of the pathogenicities of FMD (type O) viruses
isolated in Taipei China, the Republic of Korea and Japan, suggest that these
viruses might have originated as vaccine strains used in a third country.
Keywords
Asia – Foot and mouth disease – Japan – Nipah virus – Republic of Korea – Traceability –
Traceback.
Introduction
Numbering of animals by ear marking or cold branding is
practised in many countries of Asia, but the percentage of
animals that are marked to indicate their origin is rather low in
most of these countries.
The summary of responses to the questionnaire on traceback
systems sent to Chief Veterinary Officers in November 2000 is
shown in Table I. Routine traceback systems to inform animal
owners of the results of examinations at slaughterhouses are
applied in very few countries. However, in some specific
surveillance programmes, traceback systems are applied in
specified areas or zones using ear tags or other marking
methods.
The requirement for economically feasible marking systems
was discussed during the meeting held by the Office
International des Epizooties (OIE) Regional Representation
for Asia and the Pacific and the Food and Agriculture
Organization/Regional Animal Production and Health
Commission for Asia (FAO/APHCA) in New Delhi, India,
in November 1997. However, as yet, none of the
developing countries in Asia, where subregional campaigns
against rinderpest or foot and mouth disease (FMD) were
planned, have applied a nation-wide method to mark cattle
or pigs to indicate the origin of these animals for traceback
purposes.
The authors present examples of traceback efforts by
countries in Asia in response to specific epidemics, such as
Nipah virus infection in pigs in Malaysia, the FMD control
606
Rev. sci. tech. Off. int. Epiz., 20 (2)
Table I
Traceback systems used in Asia and Oceania
Country
Marking methods
Australia
Cattle tail tags (new system under test)
Authorised persons
Yes
Bhutan
–
District office
No
Ear tagging
Veterinary Organisation and affiliated branches
No
Ear tagging and microchips (cattle)
Authorised veterinarians
Yes
Laos
Identity cards
District office
Yes
Malaysia
Ear tagging
District office
No*
Iran
Certificates issued by
Traceback from abattoir?
Ear marking for vaccination
Japan
Ear tattooing
Myanmar
–
Township or District officers
Yes
Nepal
Ear tagging
District office
No
Tattooing
Quarantine station
Pakistan
–
–
No (unusual findings will be notified)
Papua New Guinea
–
Provincial/state authorities
No
Sri Lanka
–
Area veterinary officers
No
Thailand
Coloured ear tag
Quarantine station
No
Hot brand
District office
Identification cards
Vietnam
–
District office
No
* except for sero-surveillance of Nipah virus infection
programme in the Republic of Korea and the FMD
eradication programme in Japan.
Nipah virus infection in pigs
in Malaysia
History of Nipah virus
Between late September 1998 and May 1999, a new disease of
pigs, with zoonotic implications, characterised by a
pronounced respiratory and neurological syndrome and
sometimes by the sudden death of sows and boars, was
discovered in peninsular Malaysia. The disease of pigs was
found to be associated with the epidemic of viral encephalitis
which affected people with pig farming-related activities and
resulted in 265 cases of human viral encephalitis and 105
deaths. A new virus, belonging to the family Paramyxoviridae,
was discovered and named ‘Nipah’ after the village ‘Sungai
Nipah’ in which the virus was first isolated from a human case.
Molecular characterisation confirmed that the same agent was
responsible for the disease in both humans and pigs (1). The
Nipah virus is related to the Hendra virus that has killed two
people and sixteen horses in Australia since 1994.
Epidemiological background
The Nipah virus epidemic is believed to have originated in the
State of Perak and moved south, infecting other areas.
Transmission of the virus among pig farms within and between
the states of peninsular Malaysia was due to the large-scale sales
and subsequent movements of pigs. Active trading between pig
farms was normal practice in peninsular Malaysia. Farms that
did not receive animals suspected of infection remained free
from infection during the national swine testing and
surveillance programme (Phase II), although some such farms
were located immediately adjacent to an infected farm.
Although other routes of transmission between farms were
considered, for example, lorries carrying affected pigs, sharing
of boar semen and mechanical transmission by dogs and cats,
no conclusive evidence has been found to suggest that these
played a role in transmission (6, 7).
The disease was observed to spread rapidly among pigs on
infected farms. Transmission between pigs on the same farm
occurred possibly through direct contact with excretory and
secretory body fluids such as nasal mucus, saliva, pharyngeal
and bronchial secretions. The possible role of pig urine has yet
to be clarified. Pigs were kept in close confinement and acted as
a multiplying host. Mechanical transfer by dogs and cats, the
use of equipment or needles which had not been properly
sterilised for health intervention, artificial insemination or
sharing of boar semen within the farm were considered possible
means of transmission (6, 7).
The transmission studies in pigs at the Australian Animal
Health Laboratory (AAHL) of the Commonwealth Scientific
and Industrial Research Organisation (CSIRO), Australia,
607
Rev. sci. tech. Off. int. Epiz., 20 (2)
established that pigs could be infected by either the oral route
or parenteral inoculation, and demonstrated excretion of virus
via oronasal routes. Infection was observed to spread quickly to
in-contact pigs, and virus shedding from asymptomatic pigs
was demonstrated (4).
Surveillance and control measures
Surveillance programmes were divided into the following three
phases.
Phase I: stamping-out (February-March 1999)
The Department of Veterinary Services in Malaysia is
empowered under the provisions of the Animals Ordinance,
1953, to control and prevent the spread of a disease by
gazetting the new disease and identifying infected areas, disease
control areas and/or disease eradication areas. On 20 March
1999, viral encephalitis was declared by the Minister of
Agriculture to be a disease within the scope of the Ordinance
and a policy was immediately developed to eradicate the
disease by mass culling of diseased and in-contact pigs. In some
farms where deaths of humans or deaths of pigs with clinical
signs of Nipah virus infection were reported, farmers
surrendered the pigs and these animals were culled. Farms that
were abandoned by the owners were also taken over by the
Department of Veterinary Services and all the pigs were culled.
The army, police, volunteers from non-governmental
organisations, the Department of Veterinary Services and other
Government agencies were involved in the culling operation
from February to March 1999. The operation consisted of
shooting pigs, and burying the carcasses in deep pits. The
culling of pigs in these areas successfully controlled the human
epidemic in the States of Negeri Sembilan, Perak and Selangor.
During the mass culling period, farmers and residents of the
villages were evacuated from the infected areas. All inter-state
movement of pigs was also banned during this period. The
evidence of infection in dogs in an outbreak area in Sepang led
to the decision to shoot all stray dogs in infected areas at that
time. The mass culling programme for pigs was discontinued
when all the known infected farms in Perak, Negeri Sembilan
and Selangor had been depopulated. An enzyme-linked
immunosorbent assay (ELISA) was made available to identify
infected farms outside the containment areas in April 1999 (5).
Phase II: surveillance of farms and abattoirs
(April-July 1999)
A national swine testing and surveillance programme to test all
the remaining pig farms was developed to detect any infected
farms outside the containment areas. Each farm in peninsular
Malaysia is registered using a unique farm code which is used
as the basis for identification.
Serological sampling of a statistically significant number of sows
from all the pig farms was performed twice, at least three weeks
apart, because preliminary screening indicated that detection of
antibody in sows gave the highest confidence of detecting active
infection in farms. An ELISA developed by the AAHL, CSIRO,
Australia, was employed to test the sera at the Veterinary
Research Institute in Ipoh (11). The testing programme covered
a three-month period, from 21 April to 20 July, and a
provisional approval for slaughter was given to farms outside
the containment areas. Serological sampling in the farms was
conducted by teams, each of which consisted of a government
veterinary officer, a private certified veterinarian and two or
three veterinary assistants.
In addition to farm codes, global positioning system (GPS)
readings were taken for every farm during serological sampling.
No problems were encountered in the traceback of farms with
positive serology, and hence further disease control action could
be undertaken rapidly.
Simultaneously, a traceback system was established to screen
pig sera from abattoirs to provide assurance that pigs entering
the markets were uninfected. A random sampling programme
for slaughter of pigs in all the six government abattoirs and two
private abattoirs was implemented in April 2000 according to a
programme approved by the Director General of the
Department of Veterinary Services. The established farm codes
which are unique to individual farms were also used for
identification. Pigs entering abattoirs must have a farm code
tattooed on the back, and animals without farm code tattoos are
not allowed for slaughter. In the eventuality of animals giving
positive results at the abattoir, the traceback system using farm
codes to identify the affected farms was implemented and the
affected farms subjected to immediate quarantine and
classification as ‘high-risk farms’. All high-risk farms were
subjected to quarantine and given priority for testing.
A total of 896 farms (approximately 27,620 serum samples)
were tested twice over a ninety-day period. Fifty of these farms
were depopulated, based on the positive serological results.
Traceback of the affected farms was not a problem using the
farm code system.
A further 5,487 serum samples were collected from abattoirs,
and traceback of positive samples enabled the identification of
one high-risk farm. Further serological sampling and
investigation at the farm level revealed that this particular farm
was infected.
The principal difficulty encountered by the traceback system in
abattoir surveillance was the identification of farms through
farm codes tattooed on the back of animals. This was because
the tattoos were stamped by butchers themselves and the
possibility of irregularities could not be eliminated.
Phase III: surveillance of abattoirs and farms
(October 1999-October 2000)
To overcome the irregularity of farm identification in abattoirs,
an ear-notching system was made mandatory for farm
608
identification, commencing in October 1999. Ear notching was
proposed, using the international ear-notching system for all
pig farms in all states. All new-born piglets must be ear-notched
before one week of age, using the proposed state and farm
codes and these serve as a permanent identification of pigs from
a particular farm in various states when they reach abattoirs for
slaughter. From January 2000, all porkers must have
permanent ear notches when sent for slaughter in an abattoir.
Although these measures solved the problem of farm
identification, not all pig farms can be screened through
abattoir surveillance because some do not send pigs to the
government abattoirs for slaughter. To date (October 2000), the
government abattoirs have managed to cover approximately
500 farms of the 796 included in the abattoir surveillance
programme.
In March 2000, the Department of Veterinary Services decided
to screen all pig farms by randomly collecting a minimum of
thirty serum samples from breeding stock on all farms. Farms
are classified as serologically positive when positive ELISA
(immunoglobulin G) serology is confirmed by serum
neutralisation tests (SNT) at the AAHL.
Two of 796 farms screened were found to have positive
serology. Although further investigation failed to isolate any
virus, depopulation of these two affected farms in Perak was
performed, based on positive SNT results.
No new cases of Nipah virus infection have been diagnosed in
humans or pigs since the end of May 1999 (9).
Traceback investigation
of foot and mouth disease
in the Republic of Korea
Epidemiological background
Between 25 March and 15 April 2000, fifteen outbreaks of
FMD were reported in the Republic of Korea. Various control
measures, including stamping-out of infected and
neighbouring farms, movement controls and emergency
vaccination were undertaken in all affected regions.
Stamping-out was applied to all infected and neighbouring
farms within a 500-m radius, and a total of 2,216 susceptible
animals from 182 farms were destroyed.
Movement restrictions were applied to two defined zones, a
protection zone (area within a 10-km radius of the outbreak
farm) and a surveillance zone (area within a 20-km radius of
the outbreak farm). After extensive serological surveillance, all
movement restrictions were lifted on 19 July 2000.
Rev. sci. tech. Off. int. Epiz., 20 (2)
Vaccination of all susceptible livestock within the protection
zones was completed in August 2000. During the first and the
second rounds of booster vaccinations, 860,700 and 661,770
animals were vaccinated, respectively. Vaccinated animals,
except for finishing pigs to be slaughtered immediately, were
permanently marked by ear punching (pigs) and branding
(cattle, goats and deer).
By 25 August 2000, eighty-seven suspected cases had been
reported since the first outbreak. Except for the cases in the
fifteen outbreaks, the remaining seventy-two suspected cases
were later diagnosed as negative for FMD. A total of 5,400
animals from the surveillance zones and 3,568 animals from
the disease-free regions were tested using liquid phase blocking
(LPB) ELISA. In addition, a total of 8,863 vaccinated animals in
the protection zones were tested using ELISA for non-structural
protein (NSP). All samples from these zones gave negative
results when screened for FMD antibodies.
Cattle were the only animals affected during the outbreaks in
the Republic of Korea. However, the experiments performed at
the World Reference Laboratory, Pirbright, United Kingdom,
and at the Foreign Animal Disease Diagnostic Laboratory
(FADDL), Plum Island, United States of America, demonstrated
that pigs were susceptible to the Korean virus isolate
(O/SKR/2000). Sequence analysis of the VP1 gene showed close
similarity to the strains O/TAW/1/99 and O/Kinmen/TAW/99.
Traceback investigation
Although no conclusive evidence has been found to explain the
mode of entry of the FMD virus into the Republic of Korea, the
possible routes, as determined by epidemiological
investigations, are imported hay, movement of people (by
contaminated clothing, shoes, etc.) and wind-borne spread of
contaminated particles (yellow sand). Based on these findings,
farms using imported hay, imported hay samples from various
sites and yellow sand samples collected from across the country
were investigated. Other farms of epidemiological significance,
such as those that had contact through milk collection trucks
and feed delivery trucks, and those that had previously
reported illnesses with symptoms similar to FMD, were also
investigated. Clinical investigations and serological
examinations of animals on these farms were undertaken by the
provincial veterinary agencies and the National Veterinary
Research and Quarantine Service (NVRQS) as part of the FMD
Surveillance Programme. The results have been submitted to
the OIE FMD and Other Epizootics Commission.
Results
Farms using imported hay
Although imported hay was not used on any of the farms
involved in the outbreaks, it was used throughout the country.
A list of 1,823 farms was compiled, based on the records of the
companies that import hay. Of this list, 443 animals from 109
farms in the protection zones of Kyonggi Province (76 farms)
609
Rev. sci. tech. Off. int. Epiz., 20 (2)
and Chungnam Province (33 farms) were clinically
investigated. Serological examinations were also performed and
151 animals from 36 farms were tested with NSP ELISA. All
samples gave negative results when screened for FMD.
Imported hay samples
Imported hay samples were also collected from farms around
the outbreak regions and from storage facilities of various
companies that imported hay. Forty samples were collected
between March and June 2000. All samples were negative for
FMD using polymerase chain reaction (PCR) analysis (Table II).
The number of consignments and volume of imported hay and
straw used are detailed in Table III.
Table II
Samples of hay tested for foot and mouth disease virus in the
Republic of Korea by polymerase chain reaction
Sampling sites
Number of samples
Kyonggi
Chungbuk
Test results
15
Negative
2
Negative
Chungnam
4
Negative
Chonbuk
3
Negative
Kangwon
1
Negative
Storage facilities
15
Negative
Total
40
Table IV
Samples of yellow sand tested for foot and mouth disease virus
in the Republic of Korea (March-August 2000)
Area
Number of samples
Kyonggi
44
Negative
Chungbuk
17
Negative
Chungnam
15
Negative
Chonnam
2
Negative
Kangwon
19
Negative
Kyongbuk
2
Negative
Kyongnam
Total
1
100
Negative
Milk collection trucks
Clinical and serological investigation of farms that had contact
with milk collection trucks which visited farms in the outbreaks
was performed. Of 67 farms clinically investigated, 143 animals
from 15 farms were tested with NSP ELISA. All samples gave
negative results when screened for FMD (Table V).
Table V
Animals investigated on the farms that had contact with milk
collection trucks in the Republic of Korea (March-April 2000)
Province
Kyonggi
Yellow sand
Another possible route of introduction investigated was the
wind-borne spread of contaminated sand particles. One
hundred yellow sand samples were collected from across the
country between late March and early August 2000. All
samples gave negative results for FMD using PCR analysis
(Table IV).
Table III
Consignments and quantity of hay and straw imported into the
Republic of Korea (1 January-31 March 2000)
Country of origin
Item
Democratic People’s
Oak leaves
Republic of Korea
People’s Republic
of China
1
Number of
Farms
Animals
31
207
Chungbuk
0
0
Chungnam
36
36
Total
67
243
Feed delivery trucks
Farms that had contact with feed delivery trucks which made
deliveries to the farms in the outbreak areas were
investigated. Ninety-two farms were clinically investigated
and of these farms, 114 animals from twenty-eight farms
were tested with NSP ELISA. All samples gave negative
results for FMD (Table VI).
Weight
(tons)
7
Rice straw
5
2,474
Grass hay
80
21,358
Oak leaves
11
1,428
Wheat straw
28
3,577
Alfalfa
Total
Number of
consignments
Test results
Table VI
Animals investigated on the farms that had contact with feed
delivery trucks in the Republic of Korea (March-April 2000)
Province
Number of
Farms
Animals
1
33
Kyonggi
57
230
Corn stalks
15
732
Chungbuk
14
56
Corn cobs
7
798
Chungnam
21
80
148
30,407
Total
92
366
610
Rev. sci. tech. Off. int. Epiz., 20 (2)
Farms with animals presenting symptoms
Early cases of FMD were sometimes mild, showing symptoms
such as salivation, lameness, fever and respiratory problems.
Since these cases could have been overlooked, records
maintained by field veterinarians were checked to identify such
farms. Twenty-eight farms in the former protection zones had
recorded such symptoms in animals, and these farms were
clinically investigated. Of these farms, thirty-six animals from
nine farms were tested using the NSP ELISA. All samples gave
negative results for FMD (Table VII).
Table VII
Number of farms and animals presenting clinical signs of foot
and disease, Republic of Korea (March-April 2000)
Province
Kyonggi
Number of
Farms
Animals
11
44
1
4
Chungbuk
Chungnam
Total
6
24
28
72
Conclusions
Traceback investigation was performed on all farms of
epidemiological significance. By 28 October 2000, 1,088
animals from 250 farms had been clinically investigated. Of
these farms, 444 animals from 88 farms were tested by NSP
ELISA. All samples gave negative results for FMD. In addition,
forty hay samples and 100 yellow sand samples were tested by
PCR to establish the possible source of introduction. Although
all the samples were negative for FMD, additional studies are
required before ruling out hay and sand as possible sources of
infection. Delays occurred in identifying the farms, and a
number of farms had already been destocked by the time
traceback was completed and consequently could not be
investigated.
These investigations did not identify any other source of
infection or any evidence of spread of FMD. Further
investigations will be performed, including the areas outside
the outbreak zones.
employed and epidemiological investigations of the sources of
infection are detailed by Sugiura et al. (10).
Epidemiological investigations of the sources of
infection
Epidemiological studies were undertaken to investigate all
possible origins of infection (10). The potential sources
considered were infected animals, humans carrying
contaminated material (including tourists, veterinarians,
artificial inseminators, cattle claw-trimmers, owners of
animals and their families), contaminated vehicles (including
feed or animal delivery trucks and garbage collection trucks),
imported feed used in the infected areas, wind, potentially
contaminated livestock products, insects, wild animals and
pet animals.
All these potential sources of infection were ruled out by the
epidemiological investigation, except imported forage. Two
farms in which FMD was detected fed cattle with imported
forage. These farms used wheat straw imported from the
People’s Republic of China. The straw was imported during
the winter season and some straw packs contained faeces-like
substances.
Investigation of the quantity of wheat straw imported from
the People’s Republic of China revealed that the largest
volume of the imported straw from the People’s Republic of
China was consumed in Miyazaki Prefecture where the first
outbreak occurred in March 2000; the third largest amount
was consumed in Hokkaido where another outbreak
occurred in April 2000 (Table VIII). In Hokkaido, a small
amount of rice straw was also imported from Taipei China.
Table VIII
Wheat straw imported from the People’s Republic of China to
Japan (amount consumed in 1999 and stocks in June 2000)
Prefecture
Consumed in 1999
(tons)
Stock in June 2000
(tons)
Miyazaki
7,043
324
Kagoshima
6,456
297
Hokkaido
3,391
156
217
110
Others
Comparative epidemiology
Traceback investigation of foot
and mouth disease in Japan
Eradication campaign
The details of the FMD outbreaks in Japan, organisation of the
campaign, counter measures taken, surveillance systems
Straw and hay
Climatic conditions in Japan and the Republic of Korea before
March 2000 were suitable for maintaining the infectivity of
FMD viruses in the piles of hay and straw for prolonged
periods. Although attempts to detect FMD antigens in
imported hay from the People’s Republic of China gave
negative results (Table II), these results do not imply that the
611
Rev. sci. tech. Off. int. Epiz., 20 (2)
imported hay was safe for feeding cattle, as the probability of
detecting FMD viruses or antigens in a pile of hay or straw is
very low.
Even if an FMD virus or antigen were detected in the straw or
hay, a traceback to the origin of the virus would be impossible
under the present circumstances, unless the exact areas from
which this straw or hay was harvested and the data on the FMD
viruses prevalent in the harvested areas were made available,
and comparative studies were performed on those viruses.
Equally, the volume of imported straw and hay consumed in
Japan and the Republic of Korea respectively (3) was so large
that it would be impossible to ascertain that these forages were
harvested in FMD-free areas and were safe for cattle
consumption.
Further evidence that these forages were the most likely source
of infection is that FMD affected only cattle, and not pigs, both
in the Republic of Korea and Japan, despite the fact that,
experimentally, the strains of virus that originate in the Republic
of Korea and Japan are highly infectious to pigs (8).
Pathogenicity of foot and mouth disease viruses
An unusual character of the FMD virus that appeared in Taipei
China (O/TAW/99) and Japan (O/JPN/2000) was that these
strains did not produce clear signs of infection in yellow cattle
in Taipei China and in Holstein cattle in Japan, respectively (8).
These observations indicate that a variety of mild type O strains
existed in the country of origin in regard to pathogenicity in
cattle.
The strain from the Republic of Korea (O/SKR/2000) produced
visible signs of infection in both native and Holstein cattle, but
the molecular structure of the VP1 gene showed very close
similarity to the strain from Taipei China (O/TAW/99) which
gave much less clear signs of infection in yellow cattle.
Differences in pathogenicity clearly existed among the strains
isolated in the Republic of Korea, Japan and Taipei China,
although all these strains belonged to the pan-Asian topotype,
indicating that the most likely country of common origin had a
variety of type O viruses (8).
The search for such FMD viruses in the literature focused
attention on the live attenuated FMD vaccines used in the
People’s Republic of China. According to the literature
published in that country in May 1994, three types of
attenuated vaccine strains were used, two of which were type O
virus vaccines (2). Attenuated FMD type O-II vaccine for use in
cattle was developed after 130 to 146 passages in mice and
mass-produced in baby rabbits. This vaccine can be used for
adult cattle (yellow cows and yaks), adult sheep and goats, but
not for dairy cows, pigs or buffaloes. The use of the attenuated
vaccines has been officially discontinued in the People’s
Republic of China, but some people are thought to still use
them occasionally. If a live virus vaccine is used in a country, the
vaccine strain might persist in susceptible hosts by natural
passages in the field without showing clear signs of infection.
Although the OIE Emergency Meeting held in Tokyo in June
2000 strongly recommended against the use of any attenuated
vaccines for FMD (8), such a vaccine strain may remain in a
country where the attenuated vaccines were employed.
Therefore, it may be postulated that some of those FMD virus
strains which appeared in the recent epidemics in East Asia
originated from a vaccine strain(s) used in another country.
Comparative studies of the molecular structures of attenuated
vaccine strains and FMD viruses isolated in countries of the Far
East would be highly desirable.
Conclusion
Most countries of Asia need to strengthen traceability
mechanisms to determine the origins of pathogens causing new
epidemics. The origin of outbreaks of FMD in the Republic of
Korea could not be determined, despite efforts to detect the
antigens in imported hay and yellow sand. Epidemiological
studies performed in Japan to locate the origin of the FMD virus
concluded that wheat straw imported from the People’s
Republic of China was the most likely source of infection.
The origin of strains of low pathogenicity in East Asia
The occurrence of mild strains of type O virus in Taipei China
and Japan caused serious concern for those engaged in the
surveillance programmes, as these new FMD virus strains could
spread subclinically from animal to animal without manifesting
clear signs of infection.
■
612
Rev. sci. tech. Off. int. Epiz., 20 (2)
Systèmes de traçabilité ascendante utilisés lors des épizooties
récentes en Asie
Y. Ozawa, B.L. Ong & S.H. An
Résumé
Comme le montrent les réponses à un questionnaire adressé aux directions des
Services vétérinaires de treize pays asiatiques, les systèmes de traçabilité
ascendante ne sont pas encore bien développés dans la plupart des pays de la
région. Le marquage des animaux pour les besoins de la traçabilité n’est pratiqué
que dans un nombre limité de pays, dans des zones particulières et à des fins bien
précises.
La Malaisie satisfait aux exigences de la traçabilité ascendante chez les porcs en
les tatouant du code de l’élevage d’origine. Cela permet d’identifier les élevages
d’origine des porcs reconnus infectés par le virus de Nipah, lors de programmes
de sérosurveillance.
Suite à l’apparition du virus de la fièvre aphteuse en République de Corée, en mars
2000, des enquêtes épidémiologiques ont été réalisées pour rechercher les
sources possibles de contamination, par exemple le foin importé, les particules de
boue, les camions de collecte du lait et les camions de transport d’aliments pour
animaux. Aucune de ces recherches n’a permis d’identifier l’origine du virus de la
fièvre aphteuse. L’apparition du virus de la fièvre aphteuse au Japon en mars 2000
a également donné lieu à des études épidémiologiques, mais, cette fois, la paille
de blé importée a été incriminée comme la source la plus probable de l’infection.
Des études comparées sur le pouvoir pathogène des virus de la fièvre aphteuse
(type O) isolés à Taipei China, en République de Corée et au Japon, suggèrent que
ces virus ont peut-être pour origine des souches vaccinales utilisées dans un pays
tiers.
Mots-clés
Asie – Fièvre aphteuse – Japon – République de Corée – Traçabilité – Traçabilité
ascendante – Virus Nipah.
■
Sistemas de rastreo utilizados en Asia durante recientes epizootias
Y. Ozawa, B.L. Ong & S.H. An
Resumen
En la mayoría de los países asiáticos, los sistemas de rastreo son todavía
rudimentarios, como pone de manifiesto un cuestionario al que respondieron los
Servicios Veterinarios de trece países. El marcado de los animales con fines de
rastreo se practica sólo en algunos países y sólo en determinadas áreas o zonas
para cumplir con algún propósito específico.
En Malasia se han emprendido acciones de rastreo consistentes en tatuar el
código de la granja en la piel de los cerdos, lo que sirve para localizar las granjas
de origen de cerdos infectados por el virus Nipah cuando se aplican programas
de serovigilancia.
Para investigar el origen del virus de la fiebre aftosa detectado en la República de
Corea en marzo de 2000, se realizaron varios estudios epidemiológicos de
presuntas fuentes de contaminación, como heno importado, partículas de lodo o
613
Rev. sci. tech. Off. int. Epiz., 20 (2)
camiones de recogida de leche o de reparto de piensos. Ninguno de esos estudios
arrojó resultados que pudieran revelar el origen del virus de la fiebre aftosa.
También se recurrió a estudios epidemiológicos para investigar el origen del virus
de la fiebre aftosa que fue notificado en Japón en marzo de 2000, y en aquel caso
pudo determinarse que la fuente de infección más probable era una partida de
trigo importado. De una serie de estudios comparativos de la patogenicidad de los
virus de la fiebre aftosa (de tipo O) aislados en Taipei China, República de Corea y
Japón se deduce que esos virus podrían proceder de cepas de vacuna utilizadas
en algún otro país.
Palabras clave
Asia – Fiebre aftosa – Japón – Rastreabilidad – Rastreo – República de Corea –
Virus Nipah.
■
References
1. Chua K.B., Bellini W.J., Rota P.A., Harcourt B.H., Tamin A.,
Lam S.K., Ksiazek T.G., Rollin P.E., Zaki S.R., Shieh W.J.,
Goldsmith C.S., Gubler D., Roehrig J.T., Eaton B.T.,
Gould A.R., Olson J., Field H., Daniels P., Ling A.E.,
Peters C.J., Anderson L.J. & Mahy B.J. (2000). – Nipah virus:
a recently emergent deadly Paramyxovirus. Science, 288, 14321435.
2. Division of Animal Husbandry and Veterinary Medicine
(1994). – The prevention of foot and mouth disease, Appendix
3. Chinese Agriculture Technology Publishing Co., Beijing,
229-230.
3. Garner G. & Ozawa Y. (2000). – Assessment of the foot and
mouth disease situation in the Republic of Korea. In Mission
Report, Expert Mission of the Office International des
Epizooties (OIE), 6-20 May. OIE, Paris, 51 pp.
4. Middleton D., Westbury H., Morrissy C., van der Heide B.,
Russell G., Braun M., Muschialli J. & Carlson D. (2000). –
Experimental Nipah virus disease in pigs: clinical features,
virus excretion and subclinical infection. In Proc. 16th
International Pig Veterinary Society Congress, 17-20
September, Melbourne, 551-552.
5. Mohd Nor M.N. & Ong B.L. (2000). – Nipah virus infection in
animals and control measures implemented in peninsular
Malaysia. In Comprehensive reports on technical items
presented to the International Committee or to Regional
Commissions in 1999. Office International des Epizooties,
Paris, 241-250.
6. Mohd Nor M.N., Gan C.H. & Ong B.L. (2000). – Nipah virus
infection of pigs in peninsular Malaysia. In An update on
zoonoses (P.-P. Pastoret, ed.). Rev. sci. tech. Off. int. Epiz., 19 (1),
160-165.
7. Mohd Nor M.N. & Ong B.L. (2000). – The Nipah virus
outbreak and the effect on the pig industry. In Proc. 16th
International Pig Veterinary Society Congress, 17-20
September, Melbourne, 548-550.
8. Office International des Epizooties (OIE) (2000). – Report of
the OIE emergency meeting on foot and mouth disease in East
Asia, 20-22 June, Tokyo. OIE, Paris, 91 pp.
9. Ong B.L., Daniels P.W., Bunning M., Jamaluddin A.A.,
White J., Muniandy M., Olson J., Chang K.W., Morrissy C.,
Lim Y.S., Ksiazek T. & Nordin M.N. (2000). – A surveillance
program for the detection of pig herds exposed to Nipah virus
infections in peninsular Malaysia. In Proc. 9th Symposium of
the International Society for Veterinary Epidemiology and
Economics (ISVEE) (M.D. Salman, P.S. Morley & R. RuchGallie, eds), 6-11 August, Breckenridge, Colorado. ISVEE,
Department of Environmental Health, Colorado State
University, Fort Collins, Abstract ID 263. Website:
http://www.cvmbs.colostate.edu/cveadss/isvee/isvee.htm
(document accessed on 5 April 2001).
10. Sugiura K., Ogura H., Ito K., Ishikawa K., Hoshino K. &
Sakamoto K. (2001). – Eradication of foot and mouth disease
in Japan. Rev. sci. tech. Off. int. Epiz. (submitted for
publication).
11. White J.R., Narasiman M., Ramlan M., Yeoh N. Surianni,
Daniels P.W., Morrissy C., Olsen J., Crameri G., Eaton B.T. &
Jamaluddin A. (2000). – Establishment and operation of a
serological screening capacity within Malaysia for the
detection of Nipah virus antibodies in swine. In Abstracts of
the Australian Society of Microbiology Conference, July,
Cairns. Microbiol. Austr., 6, Abstract PP 5.5.