D8753.PDF

Rev. sci. tech. Off. int. Epiz., 1993, 12 (3), 817-830
Epizootiology of foot and mouth disease
in Saudi Arabia:
II. Current status on dairy farms
and control measures in operation
S.M. HAFEZ, M.A. FARAG and A. AL-SUKAYRAN *
Summary: Specifically-designed
questionnaires were distributed to the
managers and/or veterinarians of all dairy farms in Saudi Arabia in order to
obtain data on the occurrence of foot and mouth disease (FMD) on these farms
from 1971 to 1989, as well as data on current control measures. Of 39 farms, 27
responded to the questionnaire and 15 (56%) reported FMD outbreaks.
Notification and collection of samples for diagnosis were not performed
consistently. Laboratory tests were undertaken at the World Reference
Laboratory for Foot and Mouth Disease, Pirbright, United Kingdom. FMD
virus serotypes O, A and C were isolated. Epizootiological factors contributing
to the occurrence of FMD in Saudi dairy farms and recommendations
for
improving control of the disease are discussed in depth.
K E Y W O R D S : Dairy farms - Epizootiology - Foot and mouth disease Saudi Arabia.
INTRODUCTION
In order to achieve self-sufficiency in dairy products in Saudi Arabia, large modern
dairy farms have b e e n recently established in various regions of the country. T h e
establishment of these farms was initiated by the importation of pregnant Fresian and
Holstein x Fresian heifers of good breeding stock from the United States of America,
Holland, G e r m a n y and Australia. Well-planned control measures were necessary in
order to protect these valuable animals from infectious diseases prevalent in Saudi
Arabia (9, 10). At present, following the national campaign for control of rinderpest,
the most serious economic losses on Saudi dairy farms are caused by foot and mouth
disease ( F M D ) . Despite vaccination, F M D occurred regularly in some dairy farms.
Therefore, investigations into this situation w e r e necessary in o r d e r to increase
understanding of the factors contributing to the occurrence and recurrence of F M D on
these farms. Such information should help to improve current control measures.
Most dairy farms in Saudi A r a b i a employ at least one v e t e r i n a r i a n . C u r r e n t
preventive m e a s u r e s for F M D are r e l a t e d to t h e experience of these individual
veterinarians. A t the time of this study, some farms were co-operatively managed by
technical groups, e.g. Masstock (E.D. Kopel, personal communication) and Mutahidah
* National Agriculture and Water Research Centre, Ministry of Agriculture and Water,
P.O. Box 17285, Riyadh 11484, Saudi A r a b i a .
818
(S. Al-Yahya, personal communication). These groups are based in Riyadh and have
specialists in various fields of animal health and production who pay regular visits to the
farms for routine m a n a g e m e n t and the solving of any problems which arise. These
technical groups are trying to unify and standardise the disease control programmes
applied on the various farms which they manage (4).
The purpose of this study was to analyse the epizootiological aspects of F M D on
Saudi dairy farms, with special emphasis on current control measures and the likely
factors which contribute to the recurrence of the disease on some farms.
HISTORY OF FOOT A N D MOUTH DISEASE
IN S A U D I D A I R Y F A R M S
D a t a on the occurrence of F M D in the past were collected by distributing a
specifically-designed questionnaire to all dairy farms in Saudi A r a b i a (Fig. 1). The
questionnaires were distributed in August 1989 through the Director General of the
National Agriculture and Water Research Centre. Of the 39 farms which received the
questionnaire, 27 (69%) responded. Between 1971 and 1989, 37 o u t b r e a k s of F M D
occurred in 15 (56%) of the 27 farms which responded to the questionnaire (Table I).
The occurrence of F M D was reported once on five (33%) farms, twice on four (27%)
farms, three times on three (20%) farms, four times on two (13%) farms and seven times
on one (7%) farm. Samples for l a b o r a t o r y diagnosis were collected from all F M D
outbreaks on nine (60%) of the farms, and from some but not all the outbreaks on three
(20%) of the farms; no samples were collected from the F M D outbreaks on the other
three farms (Table I). Testing of samples was conducted at the Office International des
Epizooties (OIE)/Food and Agriculture Organisation of the United Nations (FAO)
World Reference L a b o r a t o r y ( W R L ) for F M D in Pirbright, U n i t e d Kingdom. The
results revealed the involvement of F M D virus serotypes O, A and C. Serotype O was
the most prevalent, while serotype C was isolated from two farms in 1984 and serotype
A was isolated from two farms in 1986 and 1987 (Table I).
A d d i t i o n a l data were also collected from the records of t h e W R L . T h e s e data
indicated the isolation of serotypes O and C from samples collected in 1983 and 1984
from two of the twelve farms which did not respond to the questionnaire. The location
of farms in which F M D outbreaks were reported is shown in Figure 1.
CURRENT FOOT A N D MOUTH DISEASE CONTROL
PROGRAMMES
Most Saudi dairy farms are considering the application of animal health measures
and immunoprophylaxis to control both the F M D viruses prevalent in the Saudi
environment and those which could be introduced through live animal importation
from enzootic countries. However, the efficacy of such measures is inconsistent.
The methods currently undertaken are detailed below.
Structural measures
Most of the farms have fences to prevent free admission to the area of the farm, and
all farms have baths in front of the entrance gates for the disinfection of vehicle wheels.
819
•
Farms which responded to the questionnaire and in which foot and mouth disease
(FMD) outbreak(s) had occurred
O F a r m s which r e s p o n d e d to the q u e s t i o n n a i r e and had n o history of p r e v i o u s
occurrence of F M D
•
Farms which did not respond to the questionnaire, but in which previous occurrence
of F M D was previously confirmed by the O I E / F A O World Reference Laboratory
for F M D
•
Farms which did not respond to the F M D questionnaire
FIG. 1
Map of Saudi Arabia showing the location of dairy farms
Functional measures
Dairy animals are imported from FMD-free countries. They are transported by air to
Saudi A r a b i a in o r d e r to avoid contact in Saudi s e a p o r t s with slaughter animals
imported from countries enzootic for F M D and other tropical diseases.
All imported animals are vaccinated upon arrival against diseases enzootic in Saudi
Arabia, including F M D . T h e vaccination p r o g r a m m e is applied according to the
instructions of the vaccine m a n u f a c t u r e r or on the basis of the experience of the
veterinarian(s) on the farm.
Some farms submit, to the vaccine p r o d u c e r s , serum samples from vaccinated
animals collected at various times post-vaccination in order to evaluate vaccine efficacy.
820
TABLE I
Data obtained from Saudi dairy farms in response to a questionnaire
occurrence of foot and mouth disease (FMD)
Location
Total no. of
animals
Year of FMD
occurrence
Laboratory
diagnosis
(Y=Yes; N=No)
regarding
FMD
serotype
Farms managed by the Masstock Technical Group
1986
2,520
Durma
1988
1983
Near Kharj
2,027
1988
1985
3,105
Tawdihia
1988
1988
Near Kharj
2,024
Y
Y
Y
Y
N
Y
Y
A
O
O
O
Farms managed by the Mutahidah Technical Group
1983
Near Kharj
2,876
1985
1987
Near Kharj
3,482
1984
1986
1987
Haradh
5,316
1987
N
N
N
Y
Y
Y
Y
-
Farms managed individually
Hofuf
260
Near Kharj
1,424
Near Kharj
Kharj
Near Kharj
Near Kharj
Najran
16,434
891
1,008
3,747
516
Experimental university farm
Riyadh
215
1971
1983
1985
1988
1982
1983
1984
1984
1986
1987
1989
1982
1983
1983
1983
1986
1987
1989
1987
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
N
Y
Y
N
Y
Y
N
1983
1985
1986
1988
N
N
Y
N
-
o
o
c
oA
O
o
o
o
o
o
o
o
c
oA
O
-
_
o
o
-
not typed
O
—
—
A
-
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Some farms produce green fodder on site in order to avoid the purchase of possibly
contaminated fodder.
If F M D is suspected, the following measures are implemented by some farms (e.g.
farms belonging to the Masstock Group):
- isolating the affected animals and placing the entire farm under quarantine
- notifying the official veterinary authority of the Ministry of Agriculture
- collecting samples for laboratory diagnosis and data for epizootiological analysis
- immediately revaccinating the entire herd against F M D
- banning all movement of vehicles, equipment and personnel to or between any
dairy farms unless specifically authorised
- requiring any p e r s o n leaving t h e farm to have a shower and change working
clothes and footwear for freshly laundered clothes and other footwear which must be
disinfected before leaving the farm
- systematically treating affected animals
- disinfecting all authorised vehicles travelling to or from the farm.
If F M D is notified, the Veterinary Authorities of the Ministry of Agriculture co­
operate with the staff of the affected farm in controlling the disease. In such a case, the
Veterinary Authority distributes an official circular to other dairy farms and district
field veterinarians informing t h e m with regard to the clinical status of F M D in t h e
various regions of the country.
POSSIBLE FACTORS CONTRIBUTING T O T H E O C C U R R E N C E
OF FOOT A N D MOUTH DISEASE
The occurrence of F M D outbreaks on dairy farms would indicate one or both of the
following:
- the introduction of F M D virus onto the farm, or the excretion of F M D virus by
carrier animals present on the farm
- the presence of non- or partially-immune animals on the farm.
When attempting to specify the factors contributing to the occurrence of F M D on
Saudi dairy farms under current field conditions in the country, it is important to analyse
the possible factors leading to the two major conditions mentioned above.
POSSIBLE FACTORS CONTRIBUTING T O T H E TRANSMISSION
AND/OR PERSISTENCE OF FOOT A N D MOUTH DISEASE VIRUS
FMD virus could be introduced onto the dairy farms via the following routes:
a) the green fodder supply
b) vehicles used for transporting milk or animals
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c) farm workers, particularly those working on more than one farm
d) visitors to the farm or merchants buying young calves from the farm
e) the presence of sheep or other range animals on the dairy farm
f) grazing of range animals not belonging to the farm (sheep, goats or camels) on the
green fodder fields
g) location of the farm on a main road leading to other dairy farms or along which
there is continuous movement of animals
h) airborne transmission of the virus over relatively long distances (6, 8)
i) passive transmission of FMD virus by birds, rodents, dogs or insects (14).
The presence of one or more of these factors was reported by all the farms on which
F M D occurred. Comparison with other dairy farms which had no previous history of
FMD showed that the factors associated with F M D transmission to Saudi farms were
numerous and complex (Table II). Nevertheless, it is clear that the Saudi dairy farms are
not absolutely isolated from the environment in which F M D virus may be circulating,
and there is continuous risk of exposure to infectious sources.
Preliminary data have indicated the presence of FMD virus carrier animals on some
dairy farms with a previous history of F M D outbreaks (11). D u e to the relatively large
numbers of animals on dairy farms in Saudi Arabia, further studies are required to
investigate the persistence on the farms of carrier strains of F M D virus and the possible
role of such strains as a potential source of infection (5, 13).
TABLE II
Frequency of factors possibly contributing to the transmission of foot and mouth
disease (FMD) virus to Saudi dairy farms
No. (%) of farms indicating
possible contribution
Factors
Farms with
previous FMD
history
(n = 15)
Farms without
previous FMD
history
(n = 12)
10 (67%)
7 (58%)
Receiving raw milk from other farms for processing
4 (27%)
1 (8%)
Selling milk to other farms
7 (47%)
8 (67%)
Exchange of staff with other farms
4 (27%)
8 (67%)
Presence of sheep in the dairy farm
2 (13%)
2 (17%)
Grazing of range animals (not belonging to the farm)
in the green fodder fields of the farm
6 (40%)
9 (75%)
Location of the farm on a main road leading
to other farms
7 (47%)
4 (33%)
Purchase of green fodder from outside the farm
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POSSIBLE FACTORS LEADING T O VACCINATION
FAILURE
Morbidity rates during F M D outbreaks on Saudi dairy farms since September 1988
ranged from 3 % to 5 3 % (unpublished findings). Some of these o u t b r e a k s occurred
among specific age groups of animals only a few weeks after t h e most r e c e n t F M D
vaccination. This vaccination failure might be due to inadequacies in the vaccine itself,
the vaccination programme(s) and/or the immune response of vaccinated animals.
Vaccine currently used in Saudi Arabia
Laboratory diagnosis of F M D outbreaks in Saudi Arabia showed the presence of a
variety of virus serotypes ( 2 , 1 1 ) . T h e F M D vaccines e m p l o y e d a r e f o r m u l a t e d to
incorporate strains which are antigenically related to the Saudi field isolates. However,
the appearance of new F M D viruses which show antigenic differences when compared
with the previously-isolated viruses raises the question of the efficacy of the vaccines
currently in use. Such was the case with F M D virus serotype A isolated from Saudi
Arabia in 1986 (18) and serotype O isolated in 1988 (19). Accordingly, it is important to
continuously monitor the antigenic profile of F M D virus strains currently circulating in
the field, in order to confirm the likelihood of the vaccine in use providing protection
against these isolates. A t present, the Saudi Veterinary Authorities are following the
advice of the W R L (where the Saudi isolates of F M D virus are subtyped and compared
with the c u r r e n t vaccine strains) r e g a r d i n g any necessity for F M D vaccine
reformulation. The vaccine presently in use is quadrivalent, incorporating serotypes O
(2 strains), A (2 strains), C and Asia 1.
In addition to antigenic specificity, the potency and freedom from residual infectivity
of the vaccine should also b e considered. Currently, batches of commercial F M D
vaccines are imported but not tested locally for potency and safety. T h e potency of a
vaccine would be reduced if the cold chain is not optimally maintained during storage
and transportation, or if the vaccine is used after the expiry date.
Vaccination programmes
Analysis of data obtained through the questionnaire revealed that most of the F M D
vaccination programmes applied were not based on clear scientific criteria. A number
of programmes are used for the primary vaccination of calves (Table III). The vaccineproducing c o m p a n i e s r e c o m m e n d that calves b o r n to vaccinated dams should b e
vaccinated with three successive doses at eight, eleven and sixteen weeks of age, and
thereafter every four m o n t h s (vaccine i m p o r t e d from t h e U n i t e d Kingdom;
C. Schermbrucker, personal communication) or with one dose at ten to twelve weeks of
age and thereafter vaccinated as for adult cattle (vaccine i m p o r t e d from F r a n c e ;
M. Lombard, personal communication). However, none of the farms applied exactly the
recommendations of the vaccine-producing companies.
The vaccine-producing companies recommend that routine herd vaccination be
performed at either four- or six-month intervals (British and French vaccines,
respectively). On Saudi dairy farms at present, herd vaccination is performed at four-, sixor twelve-month intervals, irrespective of the source of the vaccine (Table IV). A small
number of farms applying herd vaccination at four-month intervals submit serum samples
for evaluation of the immune response, but no results are available from these tests.
Due to c o n t i n u o u s changes in technical staff working on Saudi dairy farms and
unrecorded modifications in the F M D vaccination programmes applied, it is difficult to
824
TABLE
m
Programmes of primary vaccination of calves against foot and mouth disease
applied in Saudi dairy farms in 1988-1989
(FMD)
Number of doses
Age of calves
1 dose
2 doses
3 doses
0 days
O
?
3 weeks
o
O
1 month
6 weeks
2 months
O
O
O
•
10-12 weeks
11 weeks
3 months
O
C
4 months
O
5 months
6 months
O
O
[
9
i
•
•
7 months
8 months
9 months
C3
O timing and regimen of FMD vaccination applied by dairy farms
• recommended by the vaccine-producing agencies
correlate between the occurrence of F M D outbreaks in these farms and the efficacy of
vaccination programmes. Some calfhood vaccination programmes seem to commence
too early, which could result in interference from maternally-derived immunity (1, 15).
One annual dose of vaccine for routine herd vaccination will not maintain a protective
level of immunity over a long period of time. In E u r o p e , a single vaccination against
F M D is seen as a m e a n s of priming animals to develop a rapid and high level of
immunity following an emergency vaccination (16). This programme is not suitable for
dairy animals in Saudi Arabia, where there is continuous risk of exposure to F M D virus,
unlike the situation in Europe.
Variation in the immune response of individual animals
Primary vaccination of cattle of the same age and breed with a fixed dose of FMD
vaccine revealed a wide variation in serum neutralising antibody titres between
individual animals (from 1:20 to 1:720) (17). In most outbreaks on the dairy farms,
clinical cases were observed in yearling heifers or first lactation cows. Serological
investigations by enzyme-linked i m m u n o s o r b e n t assay ( E L I S A ) in one outbreak
revealed t h a t some animals in the affected age group had E L I S A titres below 1:100
(which is considered to correspond to a minimum protective level of anti-FMD virus
a n t i b o d y when m e a s u r e d by the E L I S A employed; R.P. Kitching, personal
825
TABLE I V
Foot and mouth disease herd vaccination programme
and the source of vaccine used on Saudi dairy farms in
applied
1988-1989
Number of farms using
Frequency
of vaccination
Total number
of farms
British
vaccine *
French
vaccine **
Unidentified
vaccine
16
15
-
1
Every 6 months
9
2
7
Annually
2
1
1
-
27
18
8
1
Every 4 months
Total
:
* the producer recommended repeating herd vaccination every four months
* the producer recommended repeating herd vaccination every six months
communication). Significant differences have been reported in the immune response
following F M D vaccination of three genetically-distinct strains of Fresian cattle of the
same age and u n d e r identical systems of husbandry (7). T h e possible occurrence of
genetic variation between animals on Saudi dairy farms - where artificial insemination
is performed at p r e s e n t with i m p o r t e d semen from some selected bulls - is a n o t h e r
probable factor which might cause significant differences in immune response following
FMD vaccination.
Some animals (or even a specific g r o u p of animals) may b e missed during h e r d
vaccination and/or the inoculation of some animals with lower doses of the vaccine may
occur. Consequently, certain "vaccinated" animals would be seen to be susceptible to
infection by F M D virus.
Revaccination of the dairy herd during outbreaks
When clinical cases of F M D appear on the farm, some veterinarians wrongly believe
that i m m e d i a t e revaccination of the h e r d should not be p e r f o r m e d (3). Failure to
revaccinate increases t h e force of infection and p a r t i a l l y - i m m u n e animals will b e
infected, leading to high morbidity (16). Under such conditions, revaccination with the
available vaccine is very important. This will cause an anamnestic response in partiallyimmune animals, increasing the likelihood of protective levels of immunity developing
and subsequently reducing the number of affected animals in the herd.
RECOMMENDATIONS FOR IMPROVING FOOT
AND MOUTH DISEASE CONTROL
The following recommendations have been summarised from proposals submitted
by veterinarians working on Saudi dairy farms.
Prevention of transmission of FMD
Transmission of F M D to the farm can b e p r e v e n t e d by strict application of the
following animal health measures:
826
a) purchasing green fodder from a FMD-free source
b) preventing the introduction of range animals onto the farm
c) preventing the grazing of range animals not belonging to the farm in the green
fodder of the farm
d) disinfecting the wheels of vehicles before they enter the farm
e) avoiding visits from persons having had contact with other farms and/or range and
slaughter animals
f) transporting calves and other culled animals to the m a r k e t for sale, instead of
allowing animal merchants to enter the farm.
Increasing resistance of animals
T h e resistance of animals against infection with F M D virus can be increased by
applying an effective vaccination programme, as follows:
a) using an appropriate vaccine, incorporating virus strains antigenically-related to
the F M P viruses circulating in the field
b) properly maintaining the cold chain during both transportation and storage of the
vaccine; using the vaccine before the expiry date
c) applying a standard calfhood and herd vaccination programme for all dairy farms
in the country, which should induce optimal levels of immunity for all age groups of
animals
d) conducting a serological evaluation of the efficacy of the current vaccination
programme.
Improving national FMD control
National FMD control can be improved by the establishment of effective regulatory
measures as follows:
a) implementing a nationwide vaccination campaign
b) accurately applying the F M D control regulations imposed by the Ministry of
Agriculture, with special emphasis on notifying every focus of the disease, collecting
samples for laboratory diagnosis, and applying ring vaccination and local quarantine of
animals in infected areas
c) distributing a periodical circular indicating the geographical prevalence of
important epizootics (including FMD) in the different regions of the country
d) improving the quarantine system for imported animals
e) establishing regional coordination with neighbouring countries regarding the
control of infectious animal diseases
f) organising regular meetings between the technical staff of dairy farms and
relevant officials of the Ministry of Agriculture in order to exchange information on the
current status of F M D in the field and possible means of improving control of the
disease
g) establishing a National Foot and Mouth Disease Commission.
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DISCUSSION
Control of F M D in dairy farms of countries where the disease is enzootic should be
based on simultaneous application of effective animal health m e a s u r e s and
immunoprophylaxis. D u r i n g any vaccination campaign, t h e r e will always be a
proportion of n o n - i m m u n e animals within a h e r d , e.g. animals in the following
categories:
- young animals which have not yet b e e n vaccinated and which have not b e e n
properly fed with the colostrum of vaccinated dams
- calves at the age when maternal immunity declines and which have not yet been
vaccinated
- individuals which have responded poorly to vaccination
- individuals in which immunity has waned.
Therefore, vaccination alone will not protect a dairy herd and it is dangerous to
neglect the application of efficient animal health m e a s u r e s . If the latter are not
effectively applied, the risk of transmitting F M D virus to the farm will increase, together
with the probability of non-immune animals becoming infected. Once infected, a non­
immune animal can excrete large quantities of virus. Animals in close contact, which
have a level of anti-FMD virus immunity capable of protecting against infection from
sources external to the farm, can develop F M D following the inhalation of such large
quantities of virus (16).
Emphasis should be placed on the necessity of confirming the efficacy of current
animal health measures. A standard F M D vaccination programme is also obligatory.
Primary vaccination at the age of four months is recommended, followed by a booster at
five months of age and herd vaccination at four-month intervals.
The recent establishment of local laboratory facilities to investigate the p r e s e n t
status of F M D in Saudi Arabia (11) will allow continuous surveillance of the disease
throughout the country. It is very important that laboratory diagnosis be performed for
each suspected focus of the disease among indigenous animals, in order to confirm that
the applied vaccine can protect against the F M D viruses circulating in Saudi Arabia. Of
course, this requires a continuous effort to stimulate the awareness of animal owners
and dairy farm managers to co-operate with the Veterinary Authorities of the Ministry
of Agriculture. Unfortunately, the reluctance of some dairy farms to complete the F M D
questionnaire indicates that these farms prefer not to co-operate with the national
Veterinary Services. As a result of the recent establishment of national regulations for
the control of F M D in Saudi A r a b i a (12), it is h o p e d that field staff, including
veterinarians on dairy farms, will notify the central Veterinary A u t h o r i t i e s of any
suspected focus of F M D and collect t h e a p p r o p r i a t e samples and relevant
epizootiological data.
ACKNOWLEDGEMENTS
The authors wish to thank the staff of the dairy farms who responded to the F M D
questionnaire for their kind help and co-operation.
828
This study was funded by Research Grant No. AR-10-14 of the King Abdul-Aziz
City for Science and Technology.
* *
ÉPIZOOTIOLOGIE DE LA FIÈVRE APHTEUSE EN ARABIE SAOUDITE :
II. SITUATION ACTUELLE DANS LES ÉLEVAGES LAITIERS ET MESURES
DE PROPHYLAXIE EN VIGUEUR. - S.M. Hafez, M.A. Farag et A. Al-Sukayran.
Résumé : Des questionnaires spécifiques ont été distribués aux responsables
et/ou vétérinaires de toutes les exploitations laitières d'Arabie Saoudite en vue de
recueillir des données sur l'incidence de la fièvre aphteuse dans ces élevages de
1971 à 1989, ainsi que sur les mesures prophylactiques actuellement en vigueur.
Sur 39 exploitations, 27 ont répondu au questionnaire et 15 (56 %) ont signalé
des cas de fièvre aphteuse. La collecte et la communication des prélèvements
pour diagnostic n'ont pas été réalisées régulièrement. Les épreuves de
laboratoire ont été assurées par le Laboratoire de référence mondial pour la
fièvre aphteuse de Pirbright, Royaume-Uni. Les sérotypes O, A et C du virus de
la fièvre aphteuse ont été isolés. Les facteurs épizootiologiques contribuant à
l'incidence de la fièvre aphteuse dans les exploitations laitières saoudiennes
ainsi que les recommandations pour une meilleure prophylaxie de la maladie
font l'objet d'une discussion approfondie.
MOTS-CLÉS : Arabie Saoudite - Epizootiologie - Exploitations laitières Fièvre aphteuse.
EPIZOOTIOLOGÍ A DE LA FIEBRE AFTOSA EN ARABIA SAUDÍ: II SITUACIÓN
ACTUAL EN LAS EXPLOTACIONES LECHERAS Y MEDIDAS VIGENTES
DE CONTROL. - S.M. Hafez, M.A. Farag y A. Al-Sukayran.
Resumen: Se distribuyeron cuestionarios específicos a responsables y/o
veterinarios del conjunto de las explotaciones lecheras de Arabia Saudi para
obtener datos sobre la incidencia de la fiebre aftosa en los rebaños entre 1971 y
1989, así como sobre las medidas de control actualmente vigentes. Sobre 39
explotaciones lecheras, 27 respondieron al cuestionario y 15 (56%) señalaron
casos de fiebre aftosa. La notificación y la colecta de las muestras para
diagnóstico no se llevaron a cabo con regularidad. Las pruebas de laboratorio
estuvieron a cargo del Laboratorio de referencia mundial para la fiebre aftosa de
Pirbright, Reino Unido. Se aislaron los serotipos O, A y C del virus de la fiebre
aftosa. Los autores discuten en detalle los factores epizootiológicos que
contribuyen a la incidencia de la fiebre aftosa en las explotaciones lecheras saudíes,
así como las recomendaciones que caben para un mejor control de la enfermedad.
PALABRAS CLAVE: Arabia Saudi - Epizootiología - Explotaciones
lecheras - Fiebre aftosa.
* *
829
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