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

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.

Immediate vicini ty o f Suspect Farm? Chickens vaccinated Doves/Birds vacci nated Ducks/Geese vacc inated Turkeys vacc inated

Yes 73 74 3 0

No 884 142 159 2

Total 957 216 162 2

WESTERN CAPE DEPARTMENT OF AGRICULTURE

VETERINARY SERVICES

October 2010 Volume 2, Issue 10

EPIDEMIOLOGY REPORT

Avirulent Newcastle Disease Virus in Ostriches—Oudtshoorn

Figure 1: KK Ostrich Abattoir within 10 km of suspect farm

Table 1: Birds vaccinated by the KK Abattoir between the 6th and 10th September 2010

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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

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. Alexander D J 2000 Newcastle disease in ostriches (Struthio camelus) - a review. Avian Pathol. 29: 95-100

2. Huchzermeyer F W 2002 Diseases of farmed crocodiles and ostriches. Rev.Sci.Tech. 21: 265-276

3. 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

Figure 2 : Affected ostrich farms within 10 km of suspect farm

3

5

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0 5 10 15 20 25 30

Cysticercosis

Rabies

Ovine epididymitis

Bovine

Mongoose -Large

Grey

Ovine

-New outbreaks

and cases withinthe Province -

October 2010

Total Cases during Month

New Outbreaks

2026

486

47

182

5235

8

3561

114

18

778

15

124

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Avian Bovine Canine Caprine Equine Feline Ostrich Ovine

Total vaccinations (Log Scale)

Species and Disease

- Total vaccinations recorded within the Province -

October 2010

4

5

• 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.

Outbreak Events

THE BACK PAGE VOLUME 2, ISSUE 10

John Grewar: State Vet Epidemiology

Phone: 0218085056 Cell: 0836420610

E-mail: JohnG@elsenburg.com

Lugen Govender: Data Processor - Epidemiology

Phone: 021 808 7745

E-mail: LugenG@elsenburg.com

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

Chorioptes bovis ♀ Psoroptes ovis ♀