Characterisation, experimental infection and serological response to caprine retrovirus

Longitudinal Study on Seroreactivity of Goats Exposed to Colostrum and Milk of Small Ruminant Lentivirus-infected Dams

Introduction

Small ruminant lentivirus (SRLV) causes caprine arthritis-encephalitis in goats and maedi-visna disease in sheep. Transmission is via ingestion of colostrum and milk from infected dams or long-term direct contact between animals. Lifelong seroconversion can occur several weeks after infection via ingestion. However, sub-yearling lambs that ingest contaminated colostrum may be able to clear the infection and become seronegative. Whether a similar phenomenon occurs in goats remains unknown. Therefore, the serological status of goats was studied longitudinally from the moment of natural exposure to colostrum and milk of SRLV-positive dams through the age of 24 months.

Material and Methods

Between February 2014 and March 2017 a dairy goat herd was studied which had been infected with SRLV for more than 20 years and carried maedi-visna virus-like genotype A subtype A17. Thirty-one kids born to dams seropositive for SRLV for at least a year beforehand were followed. They ingested colostrum immediately after birth and then remained with their dams for three weeks. The goats were tested serologically every month using two commercial ELISAs. The clinical condition of the goats was also regularly assessed.

Results

Out of 31 goats, 13 (42%) seroconverted at the age ranging from 3 to 22 months with a median of 5 months. Two goats seroconverted in the second year of life. The other eleven did so before the age of one year; two of these reverted to seronegative status. Only 9 out of 31 goats (29%) seroconverted in the first year of life and remained seropositive. They were early and stable seroreactors to which SRLV was transmitted lactogenically. The age at which they seroconverted ranged from 3 to 10 months with a median of 5 months. In 8 of the 18 persistently seronegative goats, a single isolated positive result occurred. No goats showed any clinical signs of arthritis. The level of maternal antibodies at the age of one week did not differ significantly between the stable seroreactors and the remainder.

Conclusion

Seroconversion appears to occur in less than 50% of goats exposed to heterologous SRLV genotype A via ingestion of colostrum and milk from infected dams and is delayed by 3-10 months. The natural lactogenic route of transmission of SRLV genotype A in goats appears to be less effective than this route of genotype B transmission reported in earlier studies.

Diagnostic tests for small ruminant lentiviruses

Maedi visna virus and caprine arthritis encephalitis virus are closely related retroviruses that cause chronic inflammatory disease in small ruminants. The infections are characterised by insidious onset and slow progression. Diagnosis of infection is usually by serological testing. A variety of assays are available for this purpose, though the relative sensitivity and specificity of these assays has not been compared systematically. Here we review recent developments in laboratory diagnostic methods and their use in field diagnosis. The results suggest that a combination of ELISA and PCR might afford optimal detection of SRLV infection.

Efficient replication of caprine arthritis-encephalitis virus in goat granulosa cells

Recent reports demonstrated the susceptibility of epithelial cells from different organs to caprine arthritis-encephalitis virus (CAEV) both in vitro and in vivo. Since granulosa cells (GC) are of epithelial origin and currently used for in vitro oocyte maturation, we addressed the question whether these cells are susceptible or resistant to CAEV infection. GC were isolated from goats from certified CAEV-free herds. PCR analysis on GC DNA using CAEV specific primers confirmed the absence of CAEV infection and immunocytochemistry using specific K813 anti-cytokeratin monoclonal antibodies confirmed the epithelial nature of GC. These cells were then inoculated with CAEV using two strains: the CAEV-pBSCA molecular clone and the CAEV-3112 French field isolate. Cytopathic effects (CPE) were observed on cell culture monolayers inoculated with both CAEV strains. Expression of CAEV proteins was shown both by immunocytochemistry using anti-p24 gag specific antibodies and by immunoprecipitation using an hyperimmune serum. Supernatant of infected cells were shown to contain high titers (ranging 10(5) tissue culture infectious doses 50 per ml: TCID(50) per ml) of infectious cytopathic viruses when assayed onto the indicator goat synovial membrane (GSM) cells. Our findings demonstrate the large cell tropism of CAEV and suggest that GC could serve as a reservoir for the virus during the sub-clinical phase of infection. Furthermore, given the high seroprevalence of CAEV in the all industrialised countries and the large number of ovaries derived from unknown serological status animals used for in vitro goat embryo production, one can conclude that these feeder cell cultures might be a potential source of early transmission of CAEV to goat embryos.

Experimental infection of Mouflon-domestic sheep hybrids with caprine arthritis-encephalitis virus

OBJECTIVE

To determine whether monocyte-derived macrophages from Mouflon-domestic sheep hybrids (Ovis musimon X Ovis spp) were susceptible to productive infection with caprine arthritis-encephalitis virus (CAEV) in vitro and whether experimental inoculation of Mouflon-domestic sheep hybrids with a molecularly cloned CAEV would result in persistent infection.

ANIMALS

5 Mouflon hybrids.

PROCEDURE

Macrophage monolayers were inoculated with virus in vitro. Three animals were inoculated with virus intratracheally.

RESULTS

Productive replication of CAEV was demonstrated in monocyte-derived macrophages following in vitro and in vivo inoculation. Titer of infectious cytopathic CAEV produced by macrophages from the Mouflon hybrids was similar to titers produced by macrophages from an infected goat or by synovial membrane cells. Isolation of virus from monocyte-derived macrophages and use of a semiquantitative polymerase chain reaction assay to amplify a portion of the viral genome demonstrated persistent virus replication in all 3 inoculated animals. Two weeks after inoculation of sheep, approximately 1 of 5,000 monocytes was harboring the virus.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicate that Mouflon-domestic sheep hybrids are susceptible to infection with isolates of CAEV that cause infection in domestic small ruminants.

The proinflammatory and chondral activities of leukemia inhibitory factor in goat joints are partially a function of interleukin-1

We wished to determine if the effects of injected recombinant human leukemia inhibitory factor (LIF) are a function of endogenous goat interleukin-1 (IL-1) production and, conversely, if the effects of injected recombinant human IL-1 are a function of endogenous LIF production in goat radiocarpal joints (RCJ). In preliminary experiments, murine LIF binding protein (MuLBP) and recombinant HuIL-1RA were found to independently attenuate the cartilage proteoglycan resorbing activity of goat synovial membrane-conditioned medium (GSMCM), implying activity against goat LIF and goat IL-1, respectively. The present study shows that the proinflammatory and chondral actions of rHuLIF in goat RCJ are partially attenuated by rHuIL-1RA. This implies that a small but important component of the in vivo activity of rHuLIF is a result of IL-1 production in the synovial joint. With the exception of proteoglycan synthesis, the absence of significant effects by MuLBP on the actions of rHuIL-1alpha in goat RCJ suggests that the proinflammatory and chondral effects of IL-1alpha in vivo are probably not mediated by LIF.

Risk factors for transmission and methods for control of caprine arthritis-encephalitis virus infection

The major route of transmission of caprine-encephalitis virus (CAEV) is through the ingestion of CAEV-infected colostrum or milk. Less efficient routes of transmission are associated with prolonged contact with infected goats and are reviewed in this article. Prevention of CAEV is based on the removal of kids from their dam at birth, and feeding the kids heat-treated colostrum and pasteurized milk until weaning. Serologic testing and segregation or culling of seropositive goats is necessary to minimize horizontal transmission of CAEV.

Immune responses in goats to caprine arthritis-encephalitis virus

In this study, goats were experimentally infected with caprine arthritis-encephalitis virus (CAEV). Anti-CAEV antibodies were detected in vivo using indirect enzyme-linked immunosorbent assay (ELISA) and Western blot assays. The results showed that the sensitivity of detection of anti-CAEV antibodies using indirect ELISA was relatively high, whereas Western blotting was very sensitive for detection of P28 anti-CAEV antibody as 4 days postinfection. Apparently, because of high immunogenicity of P28 antigen, the detection of antibodies specific for this viral protein may represent a valuable assay to detect early infection. CAEV related to other lentiviruses may be useful in studies of human immunodeficiency virus (HIV) and related viruses in animal models.

The pathology and aetiology of lung lesions in goats infected with caprine arthritis-encephalitis virus

Fifty dairy goats, of various ages, sexes and breeds were selected for examination on the basis of positive serological reactions to caprine arthritis-encephalitis virus (CAEV). Thirty-one had lung lesions including chronic interstitial pneumonia of caudal or cranioventral lobes, bronchopneumonia, verminous pneumonia, pulmonary cryptococcosis or combinations of these. The only infective agent recovered from all the chronic interstitial pneumonia cases examined was CAEV, which was also recovered from lung tissue of 3 goats with arthritis but no lung lesions. The presence of CAEV in lavaged alveolar macrophages from normal lung tissue and from lungs affected with chronic interstitial pneumonia and verminous pneumonia, and the demonstration of a marked increase in nonspecific esterase staining macrophages in areas of chronic interstitial pneumonia, are discussed in relation to the aetiology of the pneumonia.

Caprine arthritis-encephalitis virus infection of goats in South Australia

Caprine arthritis-encephalitis virus (CAEV) infection of dairy goats was shown by virus isolation and serology to be widespread in South Australia. CAEV was isolated at necropsy from 24 of 27 dairy goats with swollen joints from 13 herds, and from 9 of 30 liver dairy goats in 7 herds. Virus was isolated most frequently from synovial membranes, and occasionally from mammary glands, mammary lymph nodes, choroid plexus, lungs, spleen, bone marrow, salivary glands, leucocytes, synovial fluid and milk. Antibody to CAEV was detected in the serum of 13 of 17 of the necropsied goats tested in a single-line gel diffusion test, and in another 3 retested with a modified double-line technique. Serum antibody was also demonstrated in 61 of 77 dairy goat herds, many with histories of arthritis. In 1984 to 1986 the annual number of serologically positive serums and proportions of the numbers tested were 134 (40%), 121 (45%) and 42 (18%), respectively. CAEV was isolated from leucocytes of 8 live goats in 6 of these herds. In fibre goats antibody was detected in the serum of 25 Angora and 19 crossbreds (0.1%) from the 33,279 Angora, 1,705 Cashmere, 8,715 crossbred and 904 feral goats tested.

Caprine arthritis-encephalitis virus: an efficient method for the large scale production of serological antigens

Caprine arthritis-encephalitis virus (CAEV) was grown on a large scale in lamb corneal cell cultures. Antigens for use in two different CAEV agar gel immuno-diffusion tests were prepared from the same culture fluid. These antigens were separated on the basis of size by membrane filtration.

The effect of colostrum-derived antibody on neo-natal transmission of caprine arthritis-encephalitis virus infection

Two groups of 6 newborn goat kids were artificially fed colostrum containing antibody to caprine arthritis-encephalitis (CAE) virus, obtained from clinically affected does. Kids in group A were fed the colostrum from birth until 7 days of age, while kids in group B were fed colostrum from 1 to 3 days after birth for 7 days. Kids were fed cow's milk at all other times. Serum antibody resulting from the consumption of colostrum, detected by agar gel immunodiffusion (AGID) tests, lasted for up to 8 weeks in group A, but none was detected in group B. Four kids from each group became infected with CAE virus as demonstrated by the emergence of active immunity and by virus isolation procedures. It appeared that uptake of colostral antibody by group A did not prevent viral transmission, interfere with development of active immunity, or modify the outcome of the CAE virus infection.

A review of the sheep-multiple sclerosis connection

This paper reviews a notion that the prevalence of multiple sclerosis is high in global areas where sheep populations are concentrated. Pilot studies are reported to serum antibodies in humans to three sheep diseases; focal symmetrical encephalomalacia (FSE), maedi visna and sarcocystis. In MS patients and controls antibodies were not found to the epsilon neurotoxin of the FSE organism, Clostridium welchii type D and to a caprine retrovirus that is closely related to maedi-visna virus. However, 34% of MS and control patients had antibodies to the protozoan parasite Sarcocystis spp., tissue cysts of which contain a powerful neurotoxin, sarcocystin. It is suggested that epidemiological MS prevalence rates for country areas of southern Australia require further study along with an examination for the prevalence of MS in vegetarians.

Characteristics of cell fusion induced by a caprine retrovirus

The mechanism of cell-fusion induced by caprine arthritis-encephalitis virus (CAEV) was investigated. Following infection with concentrated CAEV, cell fusion occurred prior to the production of infectious progeny virus. The time of initial detection of cell fusion was dependent on the multiplicity of infection and was not detected until 5 hours after infection. The virus-induced cell fusion was only partially inhibited by ultraviolet irradiation of the virus and was not inhibited by cytosine arabinoside. The results indicated that fusion by CAEV was a slow response to direct interaction of input virus with cells (fusion from without) and that virus replication was not required.

A physical map of caprine arthritis-encephalitis provirus

Terminally redundant linear proviral DNA of approximately 9.5 kb was the major unintegrated species recovered in the Hirt supernatant fraction of caprine synovial membrane cells infected with strain 75-G63 caprine arthritis-encephalitis virus. A physical map based on the cleavage sites of 13 restriction endonucleases was deduced for this proviral DNA.