Characterization of small ruminant lentivirus A4 subtype isolates and assessment of their pathogenic potential in naturally infected goats.
BACKGROUND
Small ruminant lentiviruses escaping efficient serological detection are still circulating in Swiss goats in spite of a long eradication campaign that essentially eliminated clinical cases of caprine arthritis encephalitis in the country. This strongly suggests that the circulating viruses are avirulent for goats.To test this hypothesis, we isolated circulating viruses from naturally infected animals and tested the in vitro and in vivo characteristics of these field isolates.


METHODS
Viruses were isolated from primary macrophage cultures. The presence of lentiviruses in the culture supernatants was monitored by reverse transcriptase assay. Isolates were passaged in different cells and their cytopathogenic effects monitored by microscopy. Proviral load was quantified by real-time PCR using customized primer and probes. Statistical analysis comprised Analysis of Variance and Bonferroni Multiple Comparison Test.


RESULTS
The isolated viruses belonged to the small ruminant lentiviruses A4 subtype that appears to be prominent in Switzerland. The 4 isolates replicated very efficiently in macrophages, displaying heterogeneous phenotypes, with two isolates showing a pronounced cytopathogenicity for these cells. By contrast, all 4 isolates had a poor replication capacity in goat and sheep fibroblasts. The proviral loads in the peripheral blood and, in particular, in the mammary gland were surprisingly high compared to previous observations. Nevertheless, these viruses appear to be of low virulence for goats except for the mammary gland were histopathological changes were observed.


CONCLUSIONS
Small ruminant lentiviruses continue to circulate in Switzerland despite a long and expensive caprine arthritis encephalitis virus eradication campaign. We isolated 4 of these lentiviruses and confirmed their phylogenetic association with the prominent A4 subtype. The pathological and histopathological analysis of the infected animals supported the hypothesis that these A4 viruses are of low pathogenicity for goats, with, however, a caveat about the potentially detrimental effects on the mammary gland. Moreover, the high proviral load detected indicates that the immune system of the animals cannot control the infection and this, combined with the phenotypic plasticity observed in vitro, strongly argues in favour of a continuous and precise monitoring of these SRLV to avoid the risk of jeopardizing a long eradication campaign.
Martina
M
Deubelbeiss
Laure
L
Blatti-Cardinaux
Marie-Luise
ML
Zahno
Reto
R
Zanoni
Hans-Rudolf
HR
Vogt
Horst
H
Posthaus
Institute of Virology and Immunology, Vetsuisse Faculty, University of Bern, Bern, Switzerland. bertoni@vetsuisse.unibe.ch.
Giuseppe
G
Bertoni
D000818:Animals; D016088:Arthritis-Encephalitis Virus, Caprine / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity*; D001769:Blood / Q000821:virology; D002478:Cells, Cultured; D016000:Cluster Analysis; D003588:Cytopathogenic Effect, Viral; D005347:Fibroblasts / Q000821:virology; D005838:Genotype; D015511:Goat Diseases / Q000453:epidemiology / Q000821:virology*; D006041:Goats; D006801:Humans; D016180:Lentivirus Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D008264:Macrophages / Q000821:virology; D042361:Mammary Glands, Human / Q000821:virology; D008853:Microscopy; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011533:Proviruses / Q000235:genetics / Q000302:isolation & purification; D012367:RNA, Viral / Q000235:genetics; D017422:Sequence Analysis, DNA; D012756:Sheep; D013557:Switzerland / Q000453:epidemiology; D019562:Viral Load
D012367:RNA, Viral