EPIDEMIOLOGY REPORT

EPIDEMIOLOGY REPORT
Volume 2, Issue 10
October 2010
WESTERN CAPE DEPARTMENT OF AGRICULTURE
VETERINARY SERVICES
Avirulent Newcastle Disease Virus in Ostriches—Oudtshoorn
Introduction
Suspect positive virulent Newcastle disease virus (NCDV) results were obtained from samples taken during routine, annual
NCD surveillance of an ostrich farm in the Oudtshoorn district. These samples were taken on the 21 September 2010. NCD
is a controlled animal disease but, more importantly in this case, it is a trade sensitive disease for the ostrich industry.
European Union (EU) requirements on importation of ostrich meat have got several statements which refer to NCD.
In summary these consist of the following with regard to the de-boned and skinned fresh meat obtained from farmed
ratites:
• A NCD outbreak should not have occurred on the farm of origin within the last 6 months
• A NCD outbreak should not have occurred within 10 kilometres of the farm of origin within the last 3 months
• The farm of origin must have been sampled (statistically based sampling plan) for NCD surveillance, with
negative
results , for at least 6 months
• During transport to the slaughterhouse the ostriches must not come into contact with poultry and/or ratites infected with
NCD.
Outbreak Response
Due to the above requirements the State Vet service responded
immediately after receiving the suspect positive results. Movement control
measures were instituted on the farm of origin (quarantined) as well as on
registered ostrich farms within 10 kilometres of the farm of origin. The Klein
Karoo (KK) Export abattoir unfortunately fell within 10 kilometres of the
suspected outbreak (See Fig 1.) Ironically it just fell into the buffer zone, by a
few hundred meters, bringing back memories of the Linga Longa NCD
outbreak in the Swartlland in Aug/Sept last year. This immediately added a
lot of pressure and complexity to the events as restrictions on the abattoir
did not allow ostriches to be slaughtered there should their meat be
earmarked for the EU. This was not the only part of the industry to be
affected. Along with the suspect farm another 27 registered export ostrich
farms could not send birds for slaughter and export (see Fig 2 on the
Figure 1: KK Ostrich Abattoir within 10 km of suspect farm
following page). The number of ostriches within the buffer zone were
estimated to total 22 485 with +- 19 000 of these being at ready for slaughter
age. These totals do not include chicks on chick raiser farms. The events occurred in an area of Oudtshoorn which has a
number of ostrich chick raiser enterprises (n=13). These farms were also initially put under movement restrictions but these
were soon reduced as these farms are not equipped to house chicks for longer than a few days as the chicks are
generally sent to their growing farms at < 7 days old. It is fortunately standard practise for these chicks to travel under a
movement permit so monitoring these movements in conjunction with the SAOBC did not prove to be difficult.
Some epidemiological aspects of the event
A total of 120 +-6 month old ostrich chicks were trucked onto the suspect farm at the beginning of September 2010. They
were split into 2 ≈ groups which were then separated by a single strand wire fence. Only the one group of birds ever tested
positive to NCDV. On first inspection and during follow up investigations 2 weeks later no clinical signs were noted in the
birds. An evaluation was done, using the KK export abattoir vaccination data, of all NCD vaccine usage on farms near to
the suspect farm. KK abattoir vaccinates poultry in an 11 kilometre radius of the plant on a quarterly basis to produce a
zone of resistant poultry to NCD. The vaccine they use is a modified live LaSota NCD vaccine. See Table 1 for an indication
of the poultry vaccinations performed by KK abattoir during September 2010. There was definitely an indication that
LaSota vaccinations occurred quite close to the suspect farm and due to this we considered this as a possible source of
virus for the ostriches.
I mmedi ate vicini ty o f Suspe ct Farm?
Yes
No
Tot al
Chic ke ns vac cinated
73
884
957
Do ves/Birds vacci nated
74
142
216
Table 1: Birds vaccinated by the KK Abattoir between the 6th and 10th September 2010
Ducks/ Geese vacc inate d
3
159
162
Turke ys vacc inated
0
2
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VOLUME 2, ISSUE 10
Outcome
Results from increased sampling (tracheal and cloacal swabs) during the investigation were initially conflicting and
inconclusive, with antigen detection being undertaken by both Deltamune and OVI laboratories. Deltamune returned
negative results for NCDV matrix gene but OVI still had some swab pools that tested positive for NCDV matrix gene. Further
testing of these pools eventually returned positive avirulent NCDV. SPVL results for these samples were not considered as
possible contamination of the
assay took place. Based on
the avirulent test results, the
lack of clinical signs in the birds
and the proximity of poultry
NCDV
vaccinations,
movement and export control
measures were lifted. Further
clinical
surveillance
and
sampling was planned and
initiated on the suspect farm.
All in all it took 8 days
between when the first control
measures were instituted to
when they could be removed
again.
Conclusions
There
have
been
some
publications of NCD outbreaks
in ostriches. The first reports of
NCD in ostriches were in zoo
birds in the 1950’s and the
clinical symptoms there were
predominantly neurological1. It
does
seem
as
if
natural
infection
of
ostriches
results in neurological
Figure 2 : Affected ostrich farms within 10 km of suspect farm
symptoms but these may vary with age1. Some authors suggest that the
only symptoms in ostriches are typical nervous symptoms2 and, since there is no respiratory involvement, there is no
airborne transmission of the virus. Respiratory symptoms have however been noted in experimental trials3. The lack of
airborne transmission may be a reason why few birds show clinical infection during an outbreak and why the infection
does not easily transmit to other birds on the farm2. In the case in point we were initially confused as to why a group of birds
in close contact with another group failed to test positive for the disease, but in retrospect this does seem to be possible
had virulent NCD been present.
Throughout the event serological testing was also performed and the haemagglutination inhibition (HI) test was used. This
test for NCD in ostriches has had mixed reviews, with some authors not confident in the sensitivity of the test1. We initially
tested both groups (n=30 per group) of birds serologically and in duplicate. Two labs did HI testing on the same samples
and from the first group tested we got 3/30+ and 10/30+ from the labs respectively and on the second group both labs
reported 0/30+. These results didn’t give much confidence in an interlab correlation. Repeat samples were taken again
from the same 60 birds 10 days later with 0/60 returning positive results on the HI test (samples tested at only 1 lab).
Alexander1 concludes that the estimation of serum antibodies in ostriches against NCDV is not as straightforward as in other
poultry.
Positive and suspect positive NCD results create much concern and consternation, particularly when they occur in high
density ostrich farming areas and in close proximity to export abattoirs. In the space of the past 14 months two of the 4
registered export ostrich abattoirs in the Western Cape have been put under restrictions as a result of NCD.
References
1.
2.
3.
Alexander D J 2000 Newcastle disease in ostriches (Struthio camelus) - a review. Avian Pathol. 29: 95-100
Huchzermeyer F W 2002 Diseases of farmed crocodiles and ostriches. Rev.Sci.Tech. 21: 265-276
Verwoerd D J, Gerdes G H, Olivier A, Williams R 1997 Experimental infection of vaccinated slaughter ostriches with
virulent Newcastle disease virus. Onderstepoort J.Vet.Res. 64: 213-216
2
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Ovine epididymitis
Mongoose - Large
Grey
1
Rabies
Bovine
Ovine
-New outbreaks
and cases within
the Province October 2010
Cysticercosis
Total Cases during Month
1
New Outbreaks
1
26
5
0
5
10
15
20
25
30
- Total vaccinations recorded within the Province October 2010
3561
2026
778
1000
486
182
124
114
100
52
47
35
18
15
8
10
Species and Disease
3
Rabies
NCD
Enterotoxaemia
Canine
African Horse Sickness
Rabies
Distemper
Rabies
Lumpy skin disease
Botulism
Brucellosis
Bovine
Enterotoxaemia
Avian
Anthrax
1
NCD
Total vaccinations (Log Scale)
10000
Caprine
Equine
Feline
Ostrich
Ovine
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VOLUME 2, ISSUE 10
THE BACK PAGE
Outbreak Events
•
Rabies: One case of Rabies was reported late last month by the Beaufort West SV office and was not
included in the previous Epidemiology report. The case involved a bat-eared fox which showed abnormally
tame behavior by entering the yard and barn of a farmer in the Prince Albert local municipality. The farmer
shot and killed the fox and rabies was later confirmed by the Allerton laboratory. Both the rabies cases in
the Beaufort West State vet region this year have been in Bat-eared foxes. Another case of Rabies has
been reported by the Malmesbury State vet officials and it occurred in the Piketberg region. This case
occurred in a large grey mongoose which attacked a dog on a farmstead and then ran to a neighboring
house and tried to attack the farmer. It was destroyed and subsequently tested positive for rabies. There
was fortunately no evidence that the dog was bitten. There have been 4 cases of rabies in wild animals in
the Malmesbury State vet region during 2010 to date. 2 cases have been in bat-eared foxes and 1 case in
a common duiker, with the grey mongoose making up the 4th case. In total, of the 9 reported cases of
rabies this year in the Western Cape, only 1 has occurred in a domestic animal (cat) with the majority (5/9)
of cases occurring in bat-eared foxes. This is not surprising as the bat-eared fox is the enzootic host for rabies
in the region. It is very important to note however that this does not mean that bat-eared foxes are carriers
of the virus in the WC: if they get infected they will almost certainly perish. The bat-eared fox acts rather as
the maintenance host for the rabies virus variant that occurs in the WC and should the virus spill over to
another host like the domestic dog, the infection will generally not propagate further. The difficulties that
are currently facing the Johannesburg Health and Veterinary authorities is that the variant that has broken
out in their dog population is the domestic canid form, which is a variant of the virus that easily circulates
amongst susceptible domestic dogs. This is the variant that occurs endemically in KZN. The close association
of domestic dogs and humans in urban populations then predisposes the outbreak spilling over into the
human population, but again, as mentioned above, humans in this case will act as dead end hosts. The
major concern regarding rabies in the Western Cape is the ‘importation’ of the domestic canid form of the
rabies virus, as has occurred in JHB. This would cause a significant outbreak in exposed, unvaccinated
populations of dogs within our borders.
•
Sheep Scab—Alpaca’s. After further investigation on the farm of origin of the alpacas which were reported
to have sheep scab last month, it was found that the infection and clinical signs were due to a mite within
the same family, viz. Chorioptes bovis. This mite looks very similar to Psoroptes ovis (sheep scab mite) and this
is why the initial diagnosis was incorrect. The reason further investigation was done was because there were
sheep on the farm of origin as well, and they seemed not to be affected at all. This created some confusion
as there was contact between the sheep and the alpaca’s, and the sheep had every reason to become
clinically infected with sheep scab. The infection of
Chorioptes bovis must therefore be kept in mind
when these anomalies present themselves. Not only
can C. bovis affect alpacas, it is apparently a
common infection of goats in RSA. Well done to the
State officials who persisted with the investigation,
the knowledge they have exposed will help us in
future cases of this sort.
Psoroptes ovis ♀
Chorioptes bovis ♀
John Grewar: State Vet Epidemiology
Phone: 0218085056 Cell: 0836420610
E-mail: [email protected]
Lugen Govender: Data Processor - Epidemiology
Phone: 021 808 7745
E-mail: [email protected]
Disclaimer: This newsletter is published on a monthly basis for the
purpose of providing up-to-date information regarding
epidemiology of animal diseases in the Western Cape Province.
Much of the information is therefore preliminary and should not
be cited/utilised for publication
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