An outbreak of visna-maedi in a flock of sheep in Southern Brazil.

Visna-maedi is a multisystemic and progressive inflammatory disease caused by a non-oncogenic retrovirus (Visna-maedi virus, VMV). An outbreak of visna-maedi occurred in Southern Brazil in sheep with clinical signs of blindness and stumbling gait. At post-mortem examination, all animals had similar lesions, including heavy non-collapsed lungs and multifocal yellow areas in the cerebral white matter, affecting mainly the periventricular region. These lesions corresponded histologically to lymphocytic interstitial pneumonia and histiocytic periventricular encephalitis surrounding areas of necrosis, in addition to significant demyelination in the brain. Serology was performed in all the sheep from the flock and 14% were seropositive for VMV. The presence of VMV was confirmed through PCR and partial sequencing of the 5'LTR. Sequencing demonstrated that the virus had 89.7 to 90.0% of nucleotide identity with VMV strains reported in the USA. This is the first description of clinical disease related to VMV in Brazil leading to economic losses. This study calls for the need to implement control measures to prevent the spread of small ruminant lentiviruses in Brazil.

First molecular characterization of visna/maedi viruses from naturally infected sheep in Turkey.

Recent worldwide serological and genetic studies of small ruminant lentiviruses (SRLV) have led to the description of new genotypes and the development of new diagnostic tests. This study investigated the detection and molecular characterization of visna/maedi virus (VMV) infection in serum and blood samples from pure and mixed sheep breeds acquired from different regions in Turkey using ELISA and PCR techniques. The prevalence of VMV was 67.8 % by ELISA and/or LTR-PCR with both assays showing a medium level of agreement (kappa: 0.26; ± 0.038 CI). Positivity of VMV in sheep increased according to the age of the animal, although PCR positivity was higher than ELISA in young individuals. Phylogenetic analysis of 33 LTR sequences identified two distinct clades that were closely related to American and Greek LTR sequences. Phylogenetic analysis of 10 partial gag gene sequences identified A2, A3, A5, A9, A11 subtypes of genotype A SRLVs. In vitro culture of all isolates in fetal sheep lung cells (FSLC) showed a slow/low phenotype causing less or no lytic infection compared with infection with the WLC-1 American strain characterized by a rapid/highly lytic phenotype. Phylogenetic analysis revealed that Turkish VMV sequences preceded the establishment of American or Greek strains that were associated with the migration of sheep from the Middle East to Western Europe several centuries ago. This is the first study that describes Turkish VMV sequences with the molecular characterization of LTR and gag genes, and it strongly suggests that SRLV-genotype A originated in Turkey.

Maedi in slaughtered sheep: a pathology and polymerase chain reaction study in southwestern Iran.

Maedi-visna (MV) is an important slow viral disease of sheep leading to a progressive lymphoproliferative disease. It affects multiple organs primarily the lungs, where it causes interstitial pneumonia (maedi). In this study, the lungs of 1,000 sheep carcasses were grossly inspected and those suspected to have maedi were studied at histopathological and molecular levels. A polymerase chain reaction (PCR) technique that amplified a 291-base pair DNA in the long terminal repeat (LTR) sequence of MV provirus was conducted on all the 50 suspected lungs together with 10 normal appearing lungs as controls. Amplicons of the expected size were detected in 11 (n=11/50) suspected sheep, and one of the 10 control sheep. Histopathologic study of the pulmonary lesions of all 11 (n=11/11) positive sheep showed MV lesions, including hyperplasia of the perivascular and peribronchiolar lymphoid cells, interstitial lymphoplasmacytic infiltration and smooth muscle hyperplasia and the histopathologic findings were correlated with PCR results. In contrast, the tissue sections of control animals were almost normal at histopathological level; however, PCR technique demonstrated that one of them was affected by maedi. This study showed that the LTR-PCR had high specificity and sensitivity in diagnosis of this viral infection. This study is the first to evaluate the prevalence of MV virus infection in sheep in Iran.

Prevalência de anticorpos contra os agentes da maedi-visna e clamidofilose em ovinos no município de Uberlândia, MG / Prevalence of antibodies against the agents of maedi-visna and chlamydophilosis in sheep from Uberlândia county, MG, Brazil

Objetivou-se com este estudo realizar o primeiro inquérito soro-epidemiológico para o vírus da maedi-visna e Chlamydophila spp. em 12 rebanhos de ovinos do Município de Uberlândia, MG. Foram utilizadas 334 amostras de soro sanguíneo de ovinos e aplicou-se um inquérito epidemiológico a cada propriedade. Os testes realizados para a pesquisa de anticorpos contra o vírus da maedi-visna e Chlamydophila spp. foram imunodifusão em gel de ágar (IDGA) e reação de fixação do complemento (RFC), respectivamente. Não foram detectados ovinos reagentes para maedi-visna. Verificou-se uma prevalência de 3,3% para Chlamydophila spp., com títulos variando de 32 a 64. Não houve diferença estatística significativa (p > 0,05) para os fatores de risco analisados. Ressalta-se a importância dos sistemas de vigilância epidemiológica para atuar no controle dessas infecções, evitando a introdução do vírus da maedi-visna e uma maior propagação da Chlamydophila spp. neste município.

The aim of this study was to carry out the first investigation into the serological prevalence of maedi-visna virus and Chlamydophila spp. on 12 sheep breeding farms in Uberlândia County, MG, Brazil. A total of 334 blood serum samples were used and an epidemiological survey was completed by each farm. The tests to detect maedi-visna and Chlamydophila spp. antibodies were an agar gel immunodiffusion (AGID) and a complement fixation test (CFT), respectively. None of the sheep were reactive to maedi-visna. The detection of antibodies against Chlamydophila spp. was 3.3%, with titers varying from 32 to 64. There was no statistically significant difference (p > 0.05) in regard to the risk factors analyzed. The importance of epidemiological surveillance systems to aid in the control of these infections is emphasized, in order to avoid the introduction of maedi-visna virus and a wider spread of Chlamydophila spp. in this county.

Pathological and epidemiological aspects of the coexistence of maedi-visna and sheep pulmonary adenomatosis.

Between 1982 and 1991, 159 sheep suffering from chronic respiratory disease were subjected to clinical, pathological, histopathological and serological examination. Maedi was diagnosed in 82 sheep and sheep pulmonary adenomatosis (SPA) in another 59. Forty-one of the latter (69.5 per cent) were seropositive for maedi-visna (MV) virus infection, but only six (10.2 per cent) showed concurrent lung lesions of maedi. Even disregarding the MV seronegative sheep and those younger than two years old, the rate of concurrent maedi lesions did not exceed 18 per cent. During a similar period, 5060 sheep from 161 flocks (86 of which also provided the 159 affected animals) were tested for antibodies to MV virus. The average seroprevalence of MV virus infection among flocks in which SPA was detected was 66.4 per cent, whereas in those in which SPA could not be demonstrated, and in those in which necropsies were not performed, the levels of MV virus infection were 55.1 per cent and 43.6 per cent, respectively. The effect of SPA on the seroprevalence of MV virus infection was independent of other factors, such as breed of sheep or the size of the flocks. These results provide evidence that SPA plays a role in the spread of MV virus infection, although a synergistic effect of the simultaneous infection on the expression of concurrent lesions does not seem to occur.

Prevalence and effect of subclinical ovine progressive pneumonia virus infection on ewe wool and lamb production.

The prevalence of infection with ovine progressive pneumonia (OPP) virus and its effects on ewe wool and lamb production were investigated in a flock of 2,976 ewes of 6 breed types (Rambouillet, Targhee, Columbia, Polypay, 1/4 cross Finnsheep, and 1/2 cross Finnsheep). Prevalence of seropositivity was significantly (P less than or equal to 0.01) lower among Rambouillet and Targhee breeds (44 and 42%, respectively), intermediate in Polypay, Columbia, and 1/4 cross Finnsheep (approximately 53%), and higher among 1/2 cross Finnsheep (62%). Seropositivity increased with age in all breed types from 11% at 1 year of age to 93% at greater than or equal to 7 years of age. Lateral disease transmission is indicated by linear increase of seropositivity prevalence with increasing age, including that in sheep greater than 6 years old. Subclinical infection with OPP virus had no apparent detrimental effect on number of lambs born, lamb viability, birth weight, number of lambs weaned, or growth rate of single and twin lambs, compared with findings for noninfected sheep in the same flock. Mature ewe body weight and grease fleece weight did not differ between subclinically infected seropositive and seronegative ewes. Subclinical infection with OPP virus does not appear to have an adverse economic effect on ewe wool and lamb production. Culling rate attributable to clinical manifestation of infection with OPP virus must be accurately determined before the true effects of virus infection on production can be determined and an eradication program can be recommended.

Concurrent maedi-visna virus infection and pulmonary adenomatosis in a commercial breeding flock in East Anglia.

The seroprevalence of maedi-visna virus infection in thin potential cull ewes aged over two years in a flock in East Anglia increased from 3.7 per cent in August 1985 to 39.0 per cent in September 1987 and 93.3 per cent in May 1989. This increase coincided with the first appearance of sheep pulmonary adenomatosis in the flock. Four emaciated ewes which were dyspnoeic were necropsied between 1987 and 1989. Maedi and pulmonary adenomatosis were confirmed histologically in one of these ewes and pulmonary adenomatosis was confirmed in the other three.

Seroreactivity of Peruvian sheep and goats to small ruminant lentivirus-ovine progressive pneumonia virus.

Sera from 3,369 sheep and 1,394 goats in Peru were examined by agar-gel immunodiffusion for antibodies to ovine progressive pneumonia virus (OPPV). The point prevalence rates for antibodies to OPPV in sheep were 1.7% to 40.6% (mean, 19.02%) in the 7 flocks studied, whereas for goats, the point prevalence rates for antibodies that cross-reacted with OPPV in 12 herds were 0.0% to 45.1%. For sheep, a direct association between increasing age and increasing seroreactivity to OPPV was established, and there was evidence to indicate that lambs born to primiparous ewes and raised separated from all other sheep after they were weaned may have been less likely to become infected with OPPV than those lambs born to multiparous ewes and not separated from other sheep after they were weaned. For goats, antibodies to OPPV were detected in 7 of 12 herds studied, the highest infection rate being present within a herd in the Lima department (district).

Serological surveillance for maedi-visna virus and caprine arthritis-encephalitis virus in Northern Ireland.

The results of serological testing for maedi-visna virus infection in indigenous and non-indigenous sheep in Northern Ireland, over a five year period (1980 to 1984) are presented. In tests carried out in 1980 and 1981 on pedigree breeds, 10 reactors were identified on seven farms and maedi-visna virus was isolated on three occasions from leucocyte cultures. None of the animals showed clinical signs of maedi-visna and all the reactors were subsequently destroyed. Nine of the reactors were imports from Scotland or the Republic of Ireland and the other was the progeny of an imported ewe. In subsequent tests (1982 to 1984) of exotic and indigenous flocks no further reactors were identified. A survey of goat herds for evidence of caprine arthritis-encephalitis virus infection was also negative.

Investigations of a flock heavily infected with maedi-visna virus.

Following the discovery that a flock of sheep in England was infected with the virus of maedi-virus, several seropositive sheep were brought to the Central Veterinary Laboratory and kept isolated and under observation for up to three years before being further examined at necropsy. Meanwhile, sheep in the infected flock which died or were culled were examined after death for evidence of the actual disease. At necropsy pulmonary disease was a common (although not always the sole) finding, the lesions being mostly chronic pasteurellosis and pulmonary adenomatosis. One of the 45 carcases examined showed classical lesions of advanced maedi. In four others, early or incipient lesions of maedi were found in otherwise normal lungs, while in three more, maedi was coincidental with the other pulmonary diseases. No clinical evidence to suggest maedi, other than emaciation, was seen in any of the sheep with lesions of the disease.

Preliminary observations on the presence of visna-maedi in Italy.

The presence of visna-maedi in Italy is reported for the first time. History, clinical findings and gross and microscopic lesions typical of the disease were observed in two sheep flocks in Central Italy. Affected animals were afebrile, lacked energy, lost condition and had progressively worsening dyspnoea which ended fatally. A few showed locomotor disturbances but remained alert. Anaemia and leukopenia were present. The lungs were affected with fleshy consolidation. Histologically, the pulmonary lesions included bronchiolar epithelial hyperplasia, peribronchiolar lymphoid cuffing, alveolar epithelialization and very marked interstitial changes. In agar gel diffusion tests on sera from 106 animals from the two flocks, 44 were positive. Furthermore, when the same test was conducted as a preliminary screening procedure on 682 animals randomly chosen from 94 flocks in five Regions, 93 positive animals were revealed in 39 flocks, involving all of the Regions. The infection is likely to be widespread in Italy and to constitute a problem in at least some flocks or areas.