WAVLD Symposium Handbook_V4.indd - csiro

World Association of Veterinary Laboratory Diagnosticians – 13 th International Symposium, Melbourne, Australia, 11-14 November 2007
CANINE RABIES IN SOUTH AFRICA: IDENTIFICATION OF A NEW LINEAGE IN LIMPOPO AND A
RECENT SPREAD INTO THE FREE STATE PROVINCE
Introduction
Chuene Ernest Ngoepe a, * , Gugulethu Zulu a , Claude Sabeta a , Louis Nel b
a Rabies Unit, Onderstepoort Veterinary Institute, Private Bag X05, Onderstepoort, 0110
b University of Pretoria, Microbiology and Plant Pathology, 0002 Pretoria, South Africa
In 2005, there was a drastic and unexpected increase of dog rabies cases in the Limpopo province.
Laboratory confirmed cases increased from 5 in 2004 to 35 in 2005 and to 100 in 2006. The outbreak of
rabies in domestic dogs was followed by a human rabies outbreak in which at least 30 human deaths were
confirmed between 2005 and 2006. In contrast, the Free State province has been historically associated with
endemic rabies in the yellow mongoose Cynictis penicillata (Snyman, 1940; Swanepoel et al. 1993). Due to
spillover events, rabies viruses of the mongoose biotype were recovered from domestic dogs. More recently,
there has been increased number of rabies cases of the canid biotype reported in domestic dogs in this
province. The objectives of this study were; 1. to establish the exact source of infection in the human rabies
cases and the origin of the rabies virus lineage responsible for the recent rabies outbreak in Limpopo, and 2.
to trace the origin of canid rabies and assess the public health threat of mongoose rabies (in dogs) in the
Free State province.
Material & methods
A molecular epidemiological study was therefore performed on a cohort of 98 rabies viruses recovered from
domestic dogs between 1995 and 2007 from the Free State province and 52 rabies viruses recovered from
domestic dogs, jackals and humans from Limpopo and southern Zimbabwe. The cytoplasmic domain of the
glycoprotein and the G-L intergenic region of the rabies viruses in this study sample were amplified and
sequenced. Phylogenetic trees were reconstructed from an alignment of a 592-bp region of the genome
under investigation.
Results
Case 1: Phylogenetic analysis revealed that human rabies viruses were closely related to those obtained
from domestic dogs in the same locality and the rabies viruses from Limpopo were closely related to viruses
obtained from southern Zimbabwe.
Case 2: The phylogenetic analyses segregated the rabies viruses in this study sample into two main
clusters; the genetically compact canid rabies biotype and a second group of heterogeneous viruses of the
mongoose rabies biotype. From the data, it could be demonstrated that viruses of the canid rabies group
were recently introduced into this part of South Africa.
Discussions & conclusions
The reasons for the emergence and rapid dissemination of the new dog rabies strain in Limpopo are not very
clear. It appears that common rabies infection cycles persist between domestic dogs and jackals in southern
Zimbabwe and northern South Africa. It is evident that the new canid group belongs to the same
epidemiological cycle circulating in dogs in both the Free State province and across the international border
with Lesotho. Our results confirm that spillover of the mongoose biotype into domestic dogs lead to dead-end
infections. In comparison to mongoose rabies that is endemic here, canid rabies has emerged to become of
much greater importance to the public and veterinary health sectors of this region.
References
1. Swanepoel, R., Barnard, B. J. H., Meredith, C. D., Bishop, G. C., Bruckner, G. K., Fogging, C. M.,
Hubschle, O. J. B., 1993. Rabies in Southern Africa. Onderstepoort Journal of Veterinary Research, 60: pp.
325-346.
2. Snyman, P.S., 1940. The study and control of vectors of rabies in South Africa. Onderstepoort Journal of
Veterinary Science Animal Husbandry, 66: pp. 296-307
Mon 12 November
Mon 12 November
World Association of Veterinary Laboratory Diagnosticians – 13 th International Symposium, Melbourne, Australia, 11-14 November 2007
CAPRIPOXVIRUS TROPISM AND SHEDDING: A QUANTITATIVE TIME-COURSE STUDY IN
EXPERIMENTALLY INFECTED SHEEP AND GOATS
T R Bowden 1,* , S L Babiuk 2,3 , M P Anderson 1 , G R Parkyn 2 , R P Kitching 2 , J S Copps 2 and D B Boyle 1
1 CSIRO Livestock Industries, Australian Animal Health Laboratory, Private Bag 24, Geelong, Victoria 3220, Australia
2 Canadian Food Inspection Agency, National Centre for Foreign Animal Disease, 1015 Arlington Street, Winnipeg,
Manitoba R3E 3M4, Canada
3 University of Manitoba, Department of Immunology, Basic Medical Sciences Building 730 William Avenue, Winnipeg,
Manitoba R3E 0W3, Canada.
Introduction
Sheeppox virus (SPPV) and goatpox virus (GTPV), which are members of the genus Capripoxvirus in the
family Poxviridae, cause systemic disease in sheep and goats that is characterized by fever, generalized
skin nodules, lesions in the respiratory and gastrointestinal tracts and lymph node enlargement. SPPV and
GTPV are endemic in north and central Africa, the Middle East, central Asia and the Indian subcontinent,
where they are a cause of significant morbidity and mortality in susceptible sheep and goats. Despite the
considerable threat that these viruses pose to small ruminant production and to global trade in sheep, goats
and their products, knowledge of the underlying pathogenesis of sheeppox and goatpox has long been
deficient. To increase understanding of the pathogenesis of these diseases, we undertook quantitative timecourse
studies in sheep and goats, utilizing real-time PCR and traditional virological assays, following
intradermal inoculation of Nigerian SPPV or Indian GTPV in their respective homologous hosts.
Materials & methods
Nine sheep and nine goats were inoculated intradermally with either 10 4.9 TCID50 of Nigerian SPPV (sheep)
or 10 4.4 TCID50 of Indian GTPV (goats). To enable absolute quantitation of viral DNA concentrations in blood,
swabs and tissue samples, we developed a quantitative real-time PCR TaqMan assay to amplify and detect
a short product from within ORF074 of capripoxvirus genomes. Multiplexed detection of either an
endogenous or exogenous control, depending on the sample type, provided a means of verifying the
absence of PCR inhibitors in samples tested. Isolation of infectious virus from clinical materials was routinely
attempted by inoculation of samples, in duplicate, onto 80-90% confluent ovine testis cell monolayers.
Capripoxvirus-positive specimens were subsequently titrated on replicate cell monolayers to determine
sample infectivity.
Results
Viral DNA concentrations in blood, swabs, urine, faeces and solid tissues varied by as many as six orders of
magnitude. Viraemia, determined by real-time PCR and virus isolation, cleared within two to three weeks
post inoculation. Peak shedding of viral DNA and infectious virus in nasal, conjunctival and oral secretions
occurred between days 10 and 14 post inoculation, and persisted at low levels for up to an additional three to
six weeks. The highest infectious titres in nasal, conjunctival and oral swabs were observed in goats, and
correlated with the greater severity of disease observed in these animals. Although gross lesions were
evident in multiple organs at necropsy, highest viral titres were detected in skin as well as in lung and
discrete sites within oronasal tissues and gastrointestinal tract. Of all tissues tested, skin was consistently
positive throughout the sampling period.
Discussion & conclusions
Our studies have provided novel insights regarding replication, dissemination and shedding of
capripoxviruses in their natural hosts, the pathogenesis of which is similar to smallpox and monkeypox
where greatest viral replication occurs in the skin. The consistently high concentrations of viral DNA in skin,
along with its high infectivity, suggest that mechanical transmission by biting insects might occur more
frequently than previously thought. Furthermore, long term shedding of virus from mucosal surfaces
illustrates the potential for some animals to remain infectious for up to two months after the onset of fever.
These findings should facilitate development of improved strategies for detection and control of capripoxvirus
infections in sheep and goats.