Presence of Maedi Visna Virus (MVV)-Proviral DNA in the Genital Tissues of Naturally Infected Ewes

Detection and isolation of small ruminant lentivirus in the amniotic fluid of goats

The objective of this study was to verify the presence of small ruminant lentivirus in the amniotic fluid of goats using molecular tests and viral isolation by cocultivation in the amniotic fluid of naturally infected goats. The study analyzed eight goats: seven were small ruminant lentivirus-positive and one was negative. The amniotic fluid was collected from each of the eight animals during cesarean section at 147 days of pregnancy. Cocultivation was undertaken using secondary goat nictitating membrane cell cultures obtained by explant from a small ruminant lentivirus-negative calf followed by trypsinization and sub-cultivation of the cells for 63 days. During this period, five supernatant collections were performed for DNA extraction and subsequent nested polymerase chain reaction. DNA was extracted from the amniotic fluid after 3 h of cellular sedimentation, from which a sample of 600 μL was taken from the sediment and another 600 μL sample from the supernatant. After DNA extraction, nested polymerase chain reaction was performed. Of the eight goats, 62.5 % (05/08) were small ruminant lentivirus-positive, with 43.75 % (07/16) of the total samples positive when considering the two repetitions (supernatant and cell sediment). Moreover, positivity was confirmed by small ruminant lentivirus pro-viral DNA amplification in the cell supernatant throughout the cocultivation period. Small ruminant lentivirus were present in the amniotic fluid samples from the naturally infected goats indicating an intrauterine transmission route. Moreover, this biological fluid can be adopted for the diagnosis of these lentiviruse because it is an important risk factor related to intrauterine transmission.

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.

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.

Genome-wide association identifies multiple genomic regions associated with susceptibility to and control of ovine lentivirus

BACKGROUND

Like human immunodeficiency virus (HIV), ovine lentivirus (OvLV) is macrophage-tropic and causes lifelong infection. OvLV infects one quarter of U.S. sheep and induces pneumonia and body condition wasting. There is no vaccine to prevent OvLV infection and no cost-effective treatment for infected animals. However, breed differences in prevalence and proviral concentration have indicated a genetic basis for susceptibility to OvLV. A recent study identified TMEM154 variants in OvLV susceptibility. The objective here was to identify additional loci associated with odds and/or control of OvLV infection.

METHODOLOGY/PRINCIPAL FINDINGS

This genome-wide association study (GWAS) included 964 sheep from Rambouillet, Polypay, and Columbia breeds with serological status and proviral concentration phenotypes. Analytic models accounted for breed and age, as well as genotype. This approach identified TMEM154 (nominal P=9.2×10(-7); empirical P=0.13), provided 12 additional genomic regions associated with odds of infection, and provided 13 regions associated with control of infection (all nominal P<1 × 10(-5)). Rapid decline of linkage disequilibrium with distance suggested many regions included few genes each. Genes in regions associated with odds of infection included DPPA2/DPPA4 (empirical P=0.006), and SYTL3 (P=0.051). Genes in regions associated with control of infection included a zinc finger cluster (ZNF192, ZSCAN16, ZNF389, and ZNF165; P=0.001), C19orf42/TMEM38A (P=0.047), and DLGAP1 (P=0.092).

CONCLUSIONS/SIGNIFICANCE

These associations provide targets for mutation discovery in sheep susceptibility to OvLV. Aside from TMEM154, these genes have not been associated previously with lentiviral infection in any species, to our knowledge. Further, data from other species suggest functional hypotheses for future testing of these genes in OvLV and other lentiviral infections. Specifically, SYTL3 binds and may regulate RAB27A, which is required for enveloped virus assembly of human cytomegalovirus. Zinc finger transcription factors have been associated with positive selection for repression of retroviral replication. DLGAP1 binds and may regulate DLG1, a known regulator of HIV infectivity.