Maedi-Visna virus: current perspectives.

Maedi-Visna virus (MVV) and caprine arthritis-encephalitis virus are commonly known as small ruminant lentiviruses (SRLVs) due to their genetic, structural, and pathogenic similarities. They produce lifelong lasting infections in their hosts, which are characterized by slow progression till overt disease happens. There are four major clinical forms derived from a chronic inflammatory response due to the constant low grade production of viruses from monocyte-derived macrophages: respiratory (caused by interstitial pneumonia), mammary (which may produce a decrease in milk production due to subclinical mastitis), joint (characterized by lameness), and neurological (characterized by chronic nonpurulent meningoencephalomyelitis). There are three levels which try to eliminate the virus: cellular, body, and the flock level. However, SRLVs have ways to counteract these defenses. This review examines some of them.

Evolution of specific antibodies and proviral DNA in milk of small ruminants infected by small ruminant lentivirus.

The diagnosis of Small Ruminant Lentivirus (SRLV) is based on clinical signs, pathological lesions and laboratory testing. No standard reference test for the diagnosis of maedi visna has been validated up to the present, and it is puzzling that tests which detect antibodies against the virus and tests which detect the proviral genome may render opposite results. The aim of this study was to evaluate the presence in milk throughout a lactation period of specific antibodies by ELISA and of SRLV proviral DNA by a PCR of the highly conserved pol region. A six-month study was conducted with the milk of 28 ewes and 31 goats intensively reared. The percentage of animals with antibodies against SRLV increased throughout the study period. Seroprevalence in sheep was 28% at the beginning of the study and by the end it had increased up to 52.4%. In goats, initial seroprevalence of 5.6% increased to 16%. The percentage of PCR positive ewes was stable throughout the study period. Of the positive sheep, 21.4% were PCR-positive before antibodies could be detected and most of them became PCR-negative shortly after the first detection of antibodies. This might suggest that antibodies have a neutralizing effect. In addition, an equal percentage of sheep were always PCR-negative but either became ELISA-positive or was always ELISA-positive, which might support this hypothesis. On the other hand, the PCR results in goats did not follow any pattern and oscillated between 35.3% and 55.6% depending on the month. Most goats positive by PCR failed to develop antibodies in the 6 months tested. We may conclude that the infection and the antibody response to it follow a different trend in sheep and goats.

Molecular epidemiology of Streptococcus zooepidemicus isolated from the respiratory tracts of Thoroughbred racehorses in training.

The objective of this study was to characterise the molecular epidemiology of Streptococcus zooepidemicus isolated from the respiratory tracts of 198 Thoroughbred racehorses based at three Newmarket training yards over a 10 month period. Typing utilised two separate PCR procedures targeting the M-like protein hypervariable and the 16S-23S RNA gene intergenic spacer regions of the bacterium. S. zooepidemicus, isolated from 23% (224/983) of study samples, comprised 24 different types of varying prevalence. The four most common types, A1HV4, A1HV2, C1HVu and D1HV1, accounted for 45% of all the typed isolates. Overall, the findings were similar to those reported in a study of Welsh Mountain ponies and confirm that in equids, S. zooepidemicus is not a homogeneous, clonal population but instead represents a wide diversity of strain types. This diversity also highlights potential difficulties in using vaccines to control S. zooepidemicus infections in horses as it is likely that the induction of a heterologous, cross-protective immunity will be required.

Risk factors for influenza infection in vaccinated racehorses: lessons from an outbreak in Newmarket, UK in 2003.

Between March and May 2003, clinical equine influenza was confirmed among vaccinated racehorses in Newmarket, UK. A particular feature was that 2-year-old horses were apparently less susceptible than older animals. Statistical analyses comparing infected and non-infected animals showed the unusual, apparently counter-intuitive inverse age effect was principally explained by more recent vaccination among younger animals, despite broadly equivalent antibody levels between age groups. There was novel evidence for sexual dimorphism in susceptibility to infection and data supported the hypothesis that vaccination at a young age in the presence of maternally derived antibody has detrimental long-term effects on protective immunity. The practice of blanket vaccination soon after initial diagnosis ('vaccinating in the face of the outbreak') was apparently supported as a method of control. Data suggested that protective immunity conveyed by aluminium hydroxide-only adjuvanted vaccine was sub-optimal compared to other vaccine preparations.

Evidence-based immunization in horses.

Evidence of vaccine efficacy is essential for practitioners when giving advice to clients about the relative merits of different vaccines or when trying to evaluate the economic benefits of instituting a vaccine program. In equine veterinary medicine, this sort of data, which are necessary to make informed decisions about vaccine use and effectiveness, are often not available. Veterinarians need to consider the epidemiology of the disease in question, the type of vaccine that they are administering to the animal, the immunologic constraints of the vaccine technology, and the available evidence of efficacy when they are evaluating which vaccine to use or whether to vaccinate at all.

Cells infected with scrapie and Creutzfeldt-Jakob disease agents produce intracellular 25-nm virus-like particles.

We had repeatedly found approximately 25-nm-diameter virus-like particles in highly infectious brain fractions with little prion protein (PrP), and therefore we searched for similar virus-like particles in situ in infected cell lines with high titers. Neuroblastoma cells infected with the 22L strain of scrapie as well as hypothalamic GT cells infected with the FU Creutzfeldt-Jakob disease agent, but not parallel mock controls, displayed dense 25-nm virus-like particles in orthogonal arrays. These particles had no relation to abnormal PrP amyloid in situ, nor were they labeled by PrP antibodies that faithfully recognized rough endoplasmic reticulum membranes and amyloid fibrils, the predicted sites of normal and pathological intracellular PrP. Additionally, phorbol ester stimulated the production of abnormal PrP gel bands by >5-fold in infected N2a + 22L cells, yet this did not increase either the number of virus-like arrays or the infectious titer of these cells. Thus, the 25-nm infection-associated particles could not be prions. Synaptic differentiation and neurodegeneration, as well as retroviruses that populate the rough endoplasmic reticulum of neuroblastoma cells, were not required for particle production. The 25-nm particle arrays in cultured cells strongly resembled those first described in 1968 in synaptic regions of scrapie-infected brain and subsequently identified in many natural and experimental TSEs. The high infectivity of comparable, isolated virus-like particles that show no intrinsic PrP by antibody labeling, combined with their loss of infectivity when nucleic acid-protein complexes are disrupted, make it likely that these 25-nm particles are the causal TSE virions that induce late-stage PrP brain pathology.

Evaluation of a novel nested PCR for the routine diagnosis of feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV).

Laboratory diagnosis of feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) usually involves both viruses, as the clinical signs are similar and coinfection may occur. Serological methods may not represent an accurate diagnosis: maternal antibodies or cross-reactions may give false positive results to FIV, and false negative results may occur in latent FeLV status, or in certain FIV infection stages. A nested polymerase chain reaction (PCR) technique was designed to detect FeLV, FIV and feline endogenous retrovirus simultaneously. The detection of endogenous sequences was considered indicative of successful DNA extraction. The technique was used to diagnose FIV and FeLV in the blood cells of 179 cats. The kappa value with the serological data was 0.69 for FeLV and 0.87 for FIV. The joint detection of FeLV and FIV by this novel nested PCR is sensitive, specific, fast and convenient, and its applicability for clinical diagnosis is promising, as the direct evidence of the presence of the virus is more realistic than the indirect data provided by the serological detection.