Presence of caprine arthritis-encephalitis virus (CAEV) proviral DNA in genital tract tissues of superovulated dairy goat does

The genetic variability of small-ruminant lentiviruses and its impact on tropism, the development of diagnostic tests and vaccines and the effectiveness of control programmes

Introduction

Maedi-visna virus and caprine arthritis encephalitis virus are two closely related lentiviruses which cause multisystemic, progressive and persistent infection in goats and sheep. Because these viruses frequently cross the species barrier, they are considered to be one genetic group called small-ruminant lentiviruses (SRLV). They have in vivo tropism mainly for monocytes and macrophages and organ tropism with unknown mechanisms. Typical clinical signs are pneumonia in sheep, arthritis in goats, and mastitis in both species. Infection with SRLV cannot currently be treated or prevented, and control programmes are the only approaches to avoiding its spread. These programmes rely mainly on annual serological testing and elimination of positive animals. However, the high genetic and antigenic variability of SRLV complicate their early and definitive diagnosis. The objective of this review is to summarise the current knowledge of SRLV genetic variation and its implications for tropism, the development of diagnostic tests and vaccines and the effectiveness of control and eradication programmes.

Material and Methods

Subject literature was selected from the PubMed and the Google Scholar databases.

Results

The high genetic diversity of SRLV affects the performance of diagnostic tools and therefore control programmes. For the early and definitive diagnosis of SRLV infection, a combination of serological and molecular tests is suggested. Testing by PCR can also be considered for sub-yearling animals. There are still significant gaps in our knowledge of the epidemiology, immunology and biology of SRLV and their impact on animal production and welfare.

Conclusion

This information may aid selection of the most effective SRLV spread reduction measures.

Vertical transmissibility of small ruminant lentivirus

This study aimed to evaluate by means of Nested Polymerase Chain Reaction (nPCR), co-cultivation and sequencing, with genetic comparison between strains (mother/newborn), the occurrence of vertical transmission of Small Ruminant Lentiviruses (SRLV) from naturally occurring nannies infected for their offspring. For the detection of SRLV seropositive progenitors, blood was collected from 42 nannies in the final third of gestation in tubes with and without anticoagulant. The diagnostic tests used were Western Blot (WB) and nPCR. During the period of birth, the same blood collection procedure was performed on 73 newborns at zero hours of birth, with the same diagnostic tests. Seventeen blood samples from seven-day-old kids, proven positive for SRLV by nPCR, chosen at random, were subjected to coculture in goat synovial membrane (GSM) cells for 105 days. The pro-viral DNA extracted from the cell supernatant from the coculture was subjected to nPCR. For DNA sequencing from the nPCR products, nine positive samples were chosen at random, four nannies with their respective offspring, also positive. Each sample was performed in triplicate, thus generating 27 nPCR products of which only 19 were suitable for analysis. Among the 42 pregnant goats, in 50% (21/42) pro-viral DNA was detected by nPCR, while in the WB, only 7.14% (3/42) presented antibodies against SRLV. Regarding neonates, of the 73 kids, 34 (46.57%) were positive for the virus, using the nPCR technique, while in the serological test (WB), three positive animals (4.10%) were observed. The coculture of the 17 samples with a positive result in the nPCR was confirmed in viral isolation by amplification of the SRLV pro-viral DNA. When aligned, the pro-viral DNA sequences (nannies and their respective offspring) presented homology in relation to the standard strain CAEV Co. It was concluded that the transmission of SRLV through intrauterine route was potentially the source of infection in the newborn goats.

Viruses in the reproductive tract: On their way to the germ line?

Studies of vertebrate genomes have indicated that all species contain in their chromosomes stretches of DNA with sequence similarity to viral genomes. How such 'endogenous' viral elements (EVEs) ended up in host genomes is usually explained in general terms such as 'they entered the germ line at some point during evolution'. This seems a correct statement, but is also rather imprecise. The vast number of endogenous viral sequences suggest that common routes to the 'germ line' may exist, as relying on chance alone may not easily explain the abundance of EVEs in modern mammalian genomes. An increasing number of virus types have been detected in human semen and a growing number of studies have reported on viral infections that cause male infertility or subfertility and on viral infections that threaten in vitro fertilisation practices. Thus, it is timely to survey the pathway(s) that viruses can use to gain access to the human germ line. Embryo transfer and semen quality studies in livestock form another source of relevant information because virus infection during reproduction is clearly unwanted, as is the case for the human situation. In this review, studies on viruses in the male and female reproductive tract and in the early embryo will be discussed to propose a plausible viral route to the mammalian germ line.

Impact of the subclinical small ruminant lentivirus infection of female goats on the litter size and the birth body weight of kids

A longitudinal study was conducted in a single dairy goat herd to investigate the relationship between subclinical small ruminant lentivirus (SRLV) infection in does and litter size (LS) or birth body weight of kids (BW). Each year kids born to seropositive and seronegative does were weighed before the first consumption of colostrum. LS and BW of each kid were recorded. BW was significantly negatively linked to LS (p = 0.006) - singletons weighed (mean ± SD) 4.20 ± 0.67 kg, twins - 3.75 ± 0.62 kg, and triplets and quadruplets - 3.38 ± 0.47 kg. Male kids were significantly heavier than female kids in twin litters (3.97 ± 0.53 kg vs. 3.52 ± 0.60 kg; p < 0.001) and triplet or quadruplet litters (3.62 ± 0.40 kg vs. 3.17 ± 0.43 kg; p < 0.001). However, BW of male and female kids from singleton litters did not differ (4.31 ± 0.71 kg vs. 4.07 ± 0.65 kg; p = 0.154). Then, two mixed models were developed to assess the relationship between LS (mixed Poisson log linear regression model) or BW (mixed linear model) and SRLV infection in the doe, controlling for potential confounders such as the effect of an individual doe, year in which the parturition took place, parity and kid's sex. Neither LS nor BW proved to be significantly associated with SRLV infection (p = 0.788 and p = 0.214, respectively). On this basis it was concluded that LS and BW were not affected by the subclinical SRLV infection of a doe.

Small ruminant lentiviruses: economic and productive losses, consequences of the disease

ABSTRACT: Small ruminant lentiviruses, caprine arthritis encephalitis virus, and Maedi-Visna virus cause diseases that result in significant productive losses, mostly in dairy animals. These viruses belong to the Retroviridae family, Lentivirus genus, and constitute a heterogeneous group, which may generate implications for the diagnosis and control of small ruminant lentiviruses. Losses caused by them are associated with reproductive failure, short productive life, and decreased milk production by the infected animals. In addition, these viruses may reduce milk quality, affecting the production of dairy products such as cheese. Small ruminant lentiviruses lead to indirect losses, decreasing herd value and forcing the development of epidemiological trade barriers for animal germplasm. Control of small ruminant lentiviruses is important to promote optimal milk production and to reduce costs with medicine and technical assistance. This control may vary in caprine and ovine populations of each country, according to seroprevalence, variety of breeds, and peculiarities of the practiced management.

Evaluation of caprine arthritis-encephalitis virus transmission in newborn goat kids

ABSTRACT: Caprine arthritis encephalitis causes considerable losses in goat production. The main form of the caprine arthritis encephalitis virus transmission is through the ingestion of colostrum or milk from infected females. However, some transmissions cannot be explained in this manner. Therefore, this study aimed to evaluate transplacental transmission of caprine arthritis encephalitis virus. Blood samples were collected from 283 newborn kids of Anglo-Nubian and Saanen breeds born from seropositive and seronegative goats. Samples were collected immediately after birth and analyzed with agarose gel immunodiffusion and western blot. All samples were negative in the agarose gel immunodiffusion. However, the western blot test demonstrated that four kids were born positive for caprine arthritis encephalitis virus. This result indicates that although in a low frequency (1.4%), there is a possibility of transplacental transmission of small ruminant lentivirus.

The presence of small ruminant lentiviruses in Mexican Pelibuey sheep

The transmission frequency of small ruminant lentiviruses (SRLVs) through the placenta is controversial and may be associated with breed susceptibility. In Mexico, SRLV infections in sheep have been poorly studied. This work explores the presence of antibodies and proviral DNA in Mexican Pelibuey sheep. Enzyme-linked immunosorbent assays (ELISAs; three commercial kits and two on the basis of synthetic peptides) and polymerase chain reaction (PCR; amplifying the long terminal repeat and gag segments) were performed to diagnose SRLV infection in 25 adult Pelibuey ewes with an average age of 2.5 years and 32 fetuses with gestational ages ranging from 40 to 90 days without clinical signs of SRLV. Two of the three commercial ELISAs and the synthetic peptide-based ones were positive for SRLV antibody detection in 28% and 24% of the ewes, respectively, whereas none of the fetuses were positive by any of the ELISAs. By PCR, 31% of the ewes and, interestingly, two fetuses were positive. Characteristic SRLV lesions were not found in the fetal and/or ewe tissues, including those with positive PCR results. These findings demonstrate the susceptibility of Pelibuey sheep to SRLV infection and the low transmission frequency through the placenta.

Caprine arthritis encephalitis: an example of risk assessment for embryo trading

The risk of transmission of caprine arthritis encephalitis virus (CAEV) during embryo transfer has been demonstrated in vivo through the detection of CAEV proviral DNA in: (1) flushing media for embryo collection; (2) cells of the cumulus oophorus surrounding the oocytes, ovarian follicle, oviduct and uterine tissues; and (3) testis, epididymis, vas deferens and vesicular glands. Experimentally infected embryos without a zona pellucida (ZP), washed 10 times with Minimum Essential Media (MEM) and 5% Fetal Calf Serum (FCS) solution, were capable of transmitting CAEV. In vitro we demonstrated that granulosa, oviductal, epididymal and embryo cells are fully susceptible to CAEV infection and allow active replication. However, AI with in vitro-infected semen can result in the production, after ten washing, of CAEV-free embryos, and ten washing in vitro- or in vivo-infected embryos with an intact ZP, or ten washing oocytes with an intact ZP, resulted in the production of virus-free female gametes or embryos that can be used for IVF or embryo transfer. Therefore, we have demonstrated that: (1) that CAEV-free embryos can be produced by IVF using spermatozoa infected in vitro by CAEV; and (2) embryo transfer can be used under field conditions to produce CAEV-free kids from CAEV-infected biological mothers.

Seropositive bucks and within-herd prevalence of small ruminant lentivirus infection

Caprine arthritis-encephalitis is an economically important disease of goats. It is evident that horizontal transmission through respiratory secretions and milk plays an important part in the disease spread whereas the role of sexual transmission remains questionable. The cross-sectional study was carried out to investigate the relationship between presence of small ruminant lentivirus (SRL V)-seropositive bucks and seroprevalence of SRL V infection in does in herds. The analysis included 76 goat herds seropositive for SRL V infection. A sample of adult female goats from each herd was selected in a simple random fashion. All males present in a herd were also enrolled in the study. The animals were screened with commercial serological immunoenzymatic tests. Standardized questionnaires were used to gather knowledge of 3 hypothesized herd-level confounding factors: number of years for which a herd had existed until testing, goat replacement from other herds in Poland and use of machine milking. Three-level hierarchical linear regression model was developed to evaluate the relationship (α = 0.05). Median (interquartile range) within-herd seroprevalence of SRL V was 60.1% (35.7% to 87.9%) and 35.8% (10.1% to 49.6%) in herds where seropositive males were present and absent, respectively. Controlling for possible confounders presence of SRL V-seropositive bucks proved to be an independent factor linked to the higher within-herd seroprevalence of SRL V (p = 0.001). The study indicates that seropositive bucks may facilitate the spread of SRL V infection in goat herds and therefore their presence should be considered as a risk factor.

Comparative Analysis of Tat-Dependent and Tat-Deficient Natural Lentiviruses

The emergence of human immunodeficiency virus (HIV) causing acquired immunodeficiency syndrome (AIDS) in infected humans has resulted in a global pandemic that has killed millions. HIV-1 and HIV-2 belong to the lentivirus genus of the Retroviridae family. This genus also includes viruses that infect other vertebrate animals, among them caprine arthritis-encephalitis virus (CAEV) and Maedi-Visna virus (MVV), the prototypes of a heterogeneous group of viruses known as small ruminant lentiviruses (SRLVs), affecting both goat and sheep worldwide. Despite their long host-SRLV natural history, SRLVs were never found to be responsible for immunodeficiency in contrast to primate lentiviruses. SRLVs only replicate productively in monocytes/macrophages in infected animals but not in CD4+ T cells. The focus of this review is to examine and compare the biological and pathological properties of SRLVs as prototypic Tat-independent lentiviruses with HIV-1 as prototypic Tat-dependent lentiviruses. Results from this analysis will help to improve the understanding of why and how these two prototypic lentiviruses evolved in opposite directions in term of virulence and pathogenicity. Results may also help develop new strategies based on the attenuation of SRLVs to control the highly pathogenic HIV-1 in humans.

Immunogenetics of small ruminant lentiviral infections

The small ruminant lentiviruses (SRLV) include the caprine arthritis encephalitis virus (CAEV) and the Maedi-Visna virus (MVV). Both of these viruses limit production and can be a major source of economic loss to producers. Little is known about how the immune system recognizes and responds to SRLVs, but due to similarities with the human immunodeficiency virus (HIV), HIV research can shed light on the possible immune mechanisms that control or lead to disease progression. This review will focus on the host immune response to HIV-1 and SRLV, and will discuss the possibility of breeding for enhanced SRLV disease resistance.

Expanding possibilities for intervention against small ruminant lentiviruses through genetic marker-assisted selective breeding

Small ruminant lentiviruses include members that infect sheep (ovine lentivirus [OvLV]; also known as ovine progressive pneumonia virus/maedi-visna virus) and goats (caprine arthritis encephalitis virus [CAEV]). Breed differences in seroprevalence and proviral concentration of OvLV had suggested a strong genetic component in susceptibility to infection by OvLV in sheep. A genetic marker test for susceptibility to OvLV has been developed recently based on the TMEM154 gene with validation data from over 2,800 sheep representing nine cohorts. While no single genotype has been shown to have complete resistance to OvLV, consistent association in thousands of sheep from multiple breeds and management conditions highlight a new strategy for intervention by selective breeding. This genetic marker-assisted selection (MAS) has the potential to be a useful addition to existing viral control measures. Further, the discovery of multiple additional genomic regions associated with susceptibility to or control of OvLV suggests that additional genetic marker tests may be developed to extend the reach of MAS in the future. This review will cover the strengths and limitations of existing data from host genetics as an intervention and outline additional questions for future genetic research in sheep, goats, small ruminant lentiviruses, and their host-pathogen interactions.

Detecção do vírus da Artrite Encefalite Caprina por nested PCR e nested RT-PCR em ovócitos e fluido uterino

A Artrite Encefalite Caprina (CAE) é uma enfermidade infectocontagiosa causada por um vírus pertencente ao gênero lentivírus, denominado de vírus da Artrite Encefalite Caprina (CAEV). O CAEV é encontrado em vários tecidos, como o nervoso, o pulmonar, o da glândula mamária e do trato genital masculino e feminino. Desta forma, objetivou-se com este trabalho identificar a presença do CAEV, pelas técnicas de diagnóstico moleculares, em ovócitos e fluido uterino, visando avaliar a possibilidade de transmissão do CAEV pela reprodução. Foram selecionadas 13 cabras comprovadamente infectadas, as quais foram submetidas à eutanásia para coleta do aparelho reprodutor, aspiração do fluido uterino e dissecção dos ovários para coleta de ovócitos. Para identificação do CAEV nas amostras coletadas, na forma de provírus e na forma livre, foram realizadas as técnicas de PCRn e RT-PCRn, respectivamente. Observaram-se que 53,8% dos ovócitos foram positivos à técnica de RT-PCRn, enquanto apenas 9,1% foram positivos à PCRn. A técnica de RT-PCRn também identificou o vírus no fluido uterino de 46,1% das fêmeas testadas. Embora as 13 cabras em experimento fossem portadoras do CAEV, 30,8% apresentaram resultados negativos na PCRn e RT-PCRn em todas as amostras analisadas (ovócito e fluido uterino). Conclui-se que a PCRn e a RT-PCRn podem ser utilizadas no diagnóstico da CAE tendo os ovócitos e o fluido uterino como materiais de análise, e que a presença do CAEV nestes materiais aponta para o risco da transmissão do CAEV através das tecnologias reprodutivas aplicadas às fêmeas.

Development of a loop-mediated isothermal amplification method for rapid detection of caprine arthritis-encephalitis virus proviral DNA

A rapid detection assay based on loop-mediated isothermal amplification (LAMP) has been developed for detecting caprine arthritis-encephalitis (CAEV) proviral DNA. The LAMP assay utilized a set of five primers designed against highly conserved sequences located within the p25 gene region. The assay successfully detected CAEV proviral DNA in total DNA extracts originating from cell culture, whole blood samples and separated PBMCs. There was no cross-reaction with the negative control. Amplification was monitored using a Loopamp real-time turbidimeter; turbidity and the corresponding time were recorded. Amplification from CAEV-Shanxi DNA was detected as early as 17 min, with a maximum sensitivity of 0.0001 TCID(50), reached at 32 min. Sixty-eight animal blood samples were tested using AGID, PCR and LAMP assay, and the positive rates were 30.9 %, 33.8 % and 47.1 %, respectively. Whole blood can be used directly, eliminating the need for separation of PBMCs and nucleic acid extraction, reducing the overall procedure time to approximately 80 min. Therefore, the LAMP assay provides a specific and sensitive means for detecting CAEV proviral DNA in a simple, fast, and cost-effective manner and should be useful in eradication programs and epidemiological studies. Furthermore, the LAMP assay can be performed in less-well-equipped laboratories as well as in the field.

Is caprine arthritis encephalitis virus (CAEV) transmitted vertically to early embryo development stages (morulae or blastocyst) via in vitro infected frozen semen?

The aim of this study was to determine, in vivo, whether in vitro infected cryopreserved caprine sperm is capable of transmitting caprine arthritis-encephalitis virus (CAEV) vertically to early embryo development stages via artificial insemination with in vitro infected semen. Sperm was collected from CAEV-free bucks by electroejaculation. Half of each ejaculate was inoculated with CAEV-pBSCA at a viral concentration of 10(4) TCID(50)/mL. The second half of each ejaculate was used as a negative control. The semen was then frozen. On Day 13 of superovulation treatment, 14 CAEV-free does were inseminated directly into the uterus under endoscopic control with thawed infected semen. Six CAEV-free does, used as a negative control, were inseminated intrauterine with thawed CAEV-free sperm, and eight CAEV-free does were mated with naturally infected bucks. Polymerase chain reaction (PCR) was used to detect CAEV proviral-DNA in the embryos at the D7 stage, in the embryo washing media, and in the uterine secretions of recipient does. At Day 7, all the harvested embryos were PCR-negative for CAEV proviral-DNA; however, CAEV proviral-DNA was detected in 8/14 uterine smears, and 9/14 flushing media taken from does inseminated with infected sperm, and in 1/8 uterine swabs taken from the does mated with infected bucks. The results of this study confirm that (i) artificial insemination with infected semen or mating with infected bucks may result in the transmission of CAEV to the does genital tack seven days after insemination, and (ii) irrespective of the medical status of the semen or the recipient doe, it is possible to obtain CAEV-free early embryos usable for embryo transfer.

Goat uterine epithelial cells are susceptible to infection with Caprine Arthritis Encephalitis Virus (CAEV) in vivo

The aim of this study was to determine, using immunofluorescence and in situ hybridization, whether CAEV is capable of infecting goat uterine epithelial cells in vivo. Five CAEV seropositive goats confirmed as infected using double nested polymerase chain reaction (dnPCR) on leucocytes and on vaginal secretions were used as CAEV positive goats. Five CAEV-free goats were used as controls. Samples from the uterine horn were prepared for dnPCR, in situ hybridization, and immunofluorescence. The results from dnPCR confirmed the presence of CAEV proviral DNA in the uterine horn samples of infected goats whereas no CAEV proviral DNA was detected in samples taken from the uninfected control goats. The in situ hybridization probe was complementary to part of the CAEV gag gene and confirmed the presence of CAEV nucleic acids in uterine samples. The positively staining cells were seen concentrated in the mucosa of the lamina propria of uterine sections. Finally, laser confocal analysis of double p28/cytokeratin immunolabelled transverse sections of CAEV infected goat uterus, demonstrated that the virus was localized in glandular and epithelial cells. This study clearly demonstrates that goat uterine epithelial cells are susceptible to CAEV infection in vivo. This finding could help to further our understanding of the epidemiology of CAEV, and in particular the possibility of vertical transmission.

Lack of risk of transmission of caprine arthritis-encephalitis virus (CAEV) after an appropriate embryo transfer procedure

The aim of this study was to demonstrate that embryo transfer can be used to produce CAEV-free kids from CAEV-infected biological mothers when appropriate procedure is implemented. Twenty-eight goats that had tested positive for CAEV using PCR on vaginal secretions were used as embryo donors. Embryos with intact-ZP were selected and washed 10 times; they were then frozen and used for transfer into CAEV-free recipient goats. Nineteen of the 49 recipient goats gave birth, producing a total of 23 kids. Three blood samples were taken from each recipient goat, 10 days before, during, and 10 days after parturition; these were tested for CAEV antibodies using ELISA and for CAEV proviral DNA using PCR. The mothers were then euthanized. Tissue samples were taken from the lungs, udder, and retromammary and prescapular lymph nodes. The kids were separated from their mothers at birth. Seven of them died. At 4 months of age, 16 kids were subjected to drug-induced immunosuppression. Blood samples were taken every month from birth to 4 months of age; samples were then taken on days 15, 21, and 28 after the start of the immunosuppressive treatment. The kids were then euthanized and tissue samples taken from the carpal synovial membrane, lung tissue, prescapular lymph nodes, inguinal and retromammary lymph nodes, and uterus. All samples from the 19 recipient goats and 23 kids were found to be negative for CAEV antibodies and/or CAEV proviral DNA. Under acute conditions for infection this study clearly demonstrates that embryo transfer can be safely used to produce CAEV-free neonates from infected CAEV donors.

Overview of herd and CAEV status in dwarf goats in South Tyrol, Italy

The analysis of the electronic data processing proved that 323 dwarf goats older than 6 months from 165 farms were kept in 63 of the 116 communes of South Tyrol. The number of dwarf goats maintained ranged from 1 to 19 animals, the average farm size revealed to be of 2 dwarf goats/farm. 47 animals were aged between 6 months and 1 year (AG1), 97 were between 1 - 2 years of age (AG2) and 179 were aged older than 2 years (AG3). The mean age amounted to 3.8 years, the age limit being 10 years. 235 animals were female and 88 animals were male (sex ratio 2.7:1). 187 animals (57.9%) were born between November and April and 136 animals (42.1%) were born between May and October. 13 animals (4.0%) proved to possess antibodies against CAEV in a serological examination performed with ELISA. The herd seroprevalence was 6.1% (10 positive farms). The seropositivity did not vary significantly in the different age groups (AG1: 4.3%; AG2: 4.1%; AG3: 3.9%). The seroprevalence of animals born outdoors between November and April (5.9%) did not differ significantly from those born indoors between May and October (1.5%). The seroprevalence of the female animals (3.4%) did not vary significantly from that of the male goats (5.7%). The low seroprevalence ascertained in the dwarf goats in South Tyrol is due to the non-existing milk production, the marginal contact among each other as well as the sparse animal trade. This study should prompt adequate means of control to be established, so that the introduction of positive animals can be prevented. An eradication programme would be advisable, due to the low disease prevalence and its chances to be successfully implemented.

Proviral DNA of caprine arthritis encephalitis virus (CAEV) is detected in cumulus oophorus cells but not in oocytes from naturally infected goats

The aim of this study was to determine whether oocytes taken from ovarian follicles in 123 naturally infected goats were carrying the proviral CAEV genome. Examination of DNA isolated from 190 batches of oocytes with intact cumulus cells and 190 batches of oocytes whose cumulus cells had been removed, taken from follicles of the same ovaries, demonstrated that 42/190 batches of oocytes with intact cumulus cells had the proviral CAEV genome, whereas none of the 190 batches of oocytes without cumulus cells were positive for the provirus. To confirm that the proviral genome was present in the cumulus cells and not in the oocyte cells, 586 oocytes from 56 different ovaries, were separated from their cumulus cells. The DNA was then extracted from each fraction and examined. The purity of the oocyte fraction was verified by searching for granulosa cell-specific mRNA, using RT-PCR; this was negative in all the batches of oocytes in which the cumulus cells had been removed. PCR analysis demonstrated that none of the oocytes without cumulus cells were positive, whereas 22/56 of the batches with cumulus cells were found to be positive. This study clearly demonstrates that despite being surrounded by infected cumulus cells, the oocytes are not infected, and that the enzymatic and mechanical technique for removing the cells surrounding the oocyte, as used in this study, is effective, thus enabling CAEV-free oocytes to be obtained from infected goats.

Transmission of small ruminant lentiviruses

Small ruminant lentiviruses (SRLV) are classical slow retroviruses causing chronic inflammatory disease in a variety of target organs. The routes of transmission have been investigated and a large body of evidence has accumulated over many years. The main routes are through ingestion of infected colostrum and/or milk, or through inhalation of respiratory secretions. However, many studies also provide evidence that intrauterine infection may occur, though the extent and significance of this route is controversial. Embryos treated to IETS standards appear to pose very little risk of infection. SRLV have been detected in semen suggesting a potential source of transmission. However, such transmission has not been demonstrated to date. The application of control measures based on this information allows more efficient strategies to be developed which will reduce the rate of transmission.