Seropositivity for Maedi-Visna virus in sheep in Porto Acre city - Western Amazon, Brazil

Soropositividade para o vírus Maedi-Visna em ovinos da cidade de Porto Acre - Amazônia Ocidental, Brasil

Karolyne Teixeira Vinha Tamyres Izarelly Barbosa da Silva About the authors

Abstract

Lentivirosis of small ruminants (LVPR) are chronic and degenerative infectious diseases, caused by Lentivirus, associated with numerous losses such as: drop in meat and milk production, predisposition to secondary infections, expenses with veterinary assistance and, even, early disposal of animals. In the northern region of Brazil, the epidemiological situation is poorly understood. Thus, this study aimed to determine the seropositivity of sheep for Lentivirus in Porto Acre city, Western Amazon, Brazil. 122 blood samples from sheep were collected and as a diagnostic method, agarose gel immunodiffusion was used, using the p28 protein of the capsid as antigen. The seropositivity of the sheep to the test was 8.2% (10/122). In 80% (4/5) of the investigated properties, the presence of seropositive animals was detected. It is worth noting that the acquisition of small ruminants from other states likely represented a risk to sheep health in the municipality of Porto Acre, Western Amazon, Brazil. It is concluded that there is a need for more systematic investigations on the prevalence of LVPR in the state of Acre.

Keywords:
Lentivirus; Small ruminants; Amazon region; Serology

Resumo

As lentiviroses de pequenos ruminantes (LVPR) são enfermidades infecciosas crônicas e degenerativas, causadas por Lentivírus, associadas a inúmeros prejuízos como: queda na produção de carne e leite, predisposição a infecções secundárias, gastos com assistência veterinária e, até mesmo, descarte precoce dos animais. Na região norte do Brasil, a situação epidemiológica é pouco elucidada. Objetivou-se, assim, por meio deste estudo, determinar a soropositividade de ovinos para Lentivírus no município de Porto Acre, Amazônia Ocidental, Brasil. Foram coletadas 122 amostras de sangue de ovinos e como método diagnóstico foi empregada a imunodifusão em gel de agarose, utilizando a proteína p28 do capsídeo como antígeno. A soropositividade dos ovinos ao teste foi de 8,2% (10/122). Em 80% (4/5) das propriedades investigadas, detectou-se a presença de animais soropositivos. É válido ressaltar ainda que a aquisição de pequenos ruminantes advindos de outros estados provavelmente representou um risco à sanidade ovina no município de Porto Acre, Amazônia Ocidental, Brasil. Conclui-se que existe a necessidade de mais investigações sistemáticas sobre a prevalência de LVPR no estado do Acre.

Palavras-chave:
Lentivírus; Pequenos ruminantes; Região amazônica; Sorologia

Introduction

The first sheep introduced in the state of Acre came from the Northeast in the second half of the 19th century and at the beginning of the 20th century, during the period of rubber exploitation (11 Maia MS, Ribeiro VMF, Costa AL. Recomendações básicas para criação de caprinos e ovinos. Rio Branco, 1994.). Since 2004, sheep farming has grown constantly due to the intensification of meat production for self-consumption and the diversification of income in small and medium farms, with the effective number of sheep in the state at 52,559 animals (22 Monteiro AWU, Sá CP, Bayma MMA, Silva HC, Cunha ET. Tipificação da Ovinocultura no Acre. In: Congresso da Sociedade Brasileira de Economia, Administração e Sociologia Rural, 50, 2012. Anais... Vitória, 2012.,33 Instituto Brasileiro de Geografia e Estatística - IBGE. Efetivo de ovinos no município de Porto Acre. 2018. Available from: http: https://cidades.ibge.gov.br/brasil/ac/porto-acre/pesquisa/18/0 . Accessed on: 01 out. 2019.
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).

However, the sheep production chain in the state of Acre has not yet been consolidated, as the degree of technification in the properties is precarious, the extensive breeding system is prevalent and for the replacement of animals the uncontrolled natural breeding season is carried out. Product marketing logistics are also hampered by poor road infrastructure (22 Monteiro AWU, Sá CP, Bayma MMA, Silva HC, Cunha ET. Tipificação da Ovinocultura no Acre. In: Congresso da Sociedade Brasileira de Economia, Administração e Sociologia Rural, 50, 2012. Anais... Vitória, 2012.). In addition, infectious and parasitic diseases associated with insufficient technical assistance represent an important obstacle to health and productivity in herds (44 Brasil. Ministério da Agricultura, Pecuária e Abastecimento - MAPA. Manual de legislação - Programas Nacionais de Saúde Animal do Brasil. Brasília, 2009.).

Lentivirosis of small ruminants (LVPR) are infectious diseases caused by Lentiviruses (55 International Committee on Taxonomy of Viruses. Taxonomy history - ICTV. Visna-maedi vírus. 2017. Availabe from: https://talk.ictvonline.org//taxonomy/p/taxonomy-history?taxnode_id=201855035. Acessed on: 11 fev. 2020.
https://talk.ictvonline.org//taxonomy/p/...
), which result in economic losses in sheep farming and slow the growth of the production chain (66 Juste RA, Villoria M, Leginagoikoa I, Minguijon EUE. Milk production losses in Latxa dairy sheep associated with small ruminant lentivirus infection. Preventive Veterinary Medicine. 2020; 176.), however, due to their chronic evolution, they may go unnoticed by the producer (77 Gufler H. Challenges of the caprine lentivirus control programme in South Tyrol. Italy. Small Rumin. Res. 2013; 110: 112-114.). The disease triggers inflammatory, degenerative and immune-mediated lesions in the neurological, respiratory, mammary gland and joints (88 Martínez-Navalón B, Peris C, Gómez E A, Peris B, Roche M L, Caballero C, Goyena E, Berriatua E. Quantitative estimation of the impact of caprine arthritis encephalitis virus infection on milk production by dairy goats. The Veterinary Journal. 2013; 197:311-317.,99 Highland MA. Small Ruminant Lentiviruses: Strain Variation, Viral Tropism, and Host Genetics Influence Pathogenesis. Vet Pathol. 2017; 54(3):353-354.,1010 Gayo E, Polledo L, Magalde A, Balseiro A, Iglesias MJG, Martínez CP, Preziuso S, Rossi G, Marín JFG. Characterization of minimal lesions related to the presence of visna/maedi virus in the mammary gland and milk of dairy sheep. Veterinary Research. 2019; 15 (109): 1-9.) of the animals. Lentiviruses are classified into five phylogenetic groups and their viral prototypes for sheep and goats are the maedi-visna virus (MVV) and the caprine arthritis encephalitis virus (CAEV), respectively, although the possibility of interspecies transmission has already been demonstrated (1111 Gomez-Lucia E, Barquero N, Domenech A. Maedi-Visna virus: current perspectives. Veterinary Medicine. 2018; 21 (9): 11-21., 1212 Colitti B, Coradduzza E, Puggioni G, Capucchio MT, Reina R, Bertolotti L, Rosati S. A new approach for Small Ruminant Lentivirus full genome characterization revealed the circulation of divergent strains. PLoS One. 2019; 14 (2):1-12..1313 Olech M, Murawski M, Kuzmak J. Molecular analysis of small-ruminant lentiviruses in Polish flocks reveals the existence of a novel subtype in sheep. Archives of Virology. 2019; 164 (4):1193-1198.).

In the northern region, the lentivirosis of small ruminants and the impacts on production are only described in the states of Amazonas (1414 Lima NS. Incidência de Maedi-Visna na população de ovinos (Ovis aries) em propriedades rurais da região metropolitana de Manaus - AM. 2011. 35f. Dissertação (Mestrado em Medicina Veterinária) - Escola Superior Batista do Amazonas, Manaus, 2011.) and Tocantins (1515 Sobrinho PAM, Fernandes CHC, Ramos TRR, Campos AC, Costa LM, Castro RS. Prevalência e fatores associados à infecção por lentivírus de pequenos ruminantes em ovinos no estado do Tocantins. Ciência Veterinária nos Trópicos. 2008; 11(2/3):65-72.,1616 Mazzinghy CL, Almeida KDS, Veschi JLA, Castro RSD, Martins NEX, Sousa MG. Frequency of antibodies against ovine Lentivirus in sheep in Colinas do Tocantins, Tocantins state, Brazil. Arquivos do Instituto Biológico. 2016; 86.). It is believed that the survey of epidemiological data in a region can bring relevant information about viral circulation and possible risk factors, allowing for better planning of prophylactic measures and control of lentivirosis in herds, and minimizing impacts by decreasing the production of meat and milk, birth of weak offspring, the predisposition to secondary infections, early slaughter and commercial embargoes (1717 Minguijon E, Reina R, Perez M, Polledo L, Villoria M, Ramirez H, Leginagoikoa I, Badiola JJ, Garcia-Marin JF, Andres D. Small ruminant lentivirus infections and diseases. Veterinary. Microbiology. 2015; 181: 75-89.).

Thus, the objective of this study was to determine the seropositivity of sheep for maedi-visna virus in the municipality of Porto Acre, Western Amazon, Brazil, given that the situation in the state of Acre is still unknown.

Material and methods

This study was approved by the Animal Use Ethics Committee of the Federal University of Acre, under authorization No. 29/2017.

The state of Acre is located in the southwest of the northern region of Brazil in the Western Amazon, and is bordered by the Amazon to the north, Rondônia to the east, Bolivia to the southeast and Peru to the south and west. The region has an equatorial climate, with temperatures ranging between 25 and 40 ° C and forest vegetation in the Amazon. The state’s territorial extension is 152,581,388 km2, comprising 22 municipalities.

According to the last agricultural census, the population of sheep in the state is 52,557 heads, of which 5,544 animals are allocated in the municipality of Porto Acre (09 ° 35’18 ”S; 67 ° 31’57” W) (33 Instituto Brasileiro de Geografia e Estatística - IBGE. Efetivo de ovinos no município de Porto Acre. 2018. Available from: http: https://cidades.ibge.gov.br/brasil/ac/porto-acre/pesquisa/18/0 . Accessed on: 01 out. 2019.
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); area selected for the study because it is provided with a program to strengthen the sheep chain, in addition to factors such as access to the property, the infrastructure of the place and the availability of producers to participate in the study.

The sample size calculation was based on descriptive epidemiological studies (1818 Rouquayrol MZ, Gurgel M. Epidemiologia e Saúde. 8 ed. Rio de Janeiro: MedBook, 2017. 744p.,1919 Alves SM, Teixeira MFS, Pinheiro RR, Alves FSF, Lima AMC, de Farias DA, Aguiar TDAF. Seroepidemiological study of maedi-visna in sheep in Ceara, Rio Grande do Norte, Paraíba and Sergipe States. Semina: Ciências Agrárias. 2018; 39(5): 2017-2028.). The estimated prevalence was 1.62% (1414 Lima NS. Incidência de Maedi-Visna na população de ovinos (Ovis aries) em propriedades rurais da região metropolitana de Manaus - AM. 2011. 35f. Dissertação (Mestrado em Medicina Veterinária) - Escola Superior Batista do Amazonas, Manaus, 2011.), with a 95% confidence interval and statistical error of 5%, requiring at least 118 samples. For non-probabilistic convenience, five properties were selected in the municipality of Porto Acre, of which 20 to 25 animals were randomly assigned to the study, totaling 122 sheep. The profile of the studied population was then constituted by animals with aptitude for cutting, being 88 females and 34 males, of the Dorper races (4.1% - 5/122), Santa Inês (25.4% - 12/31) or without defined race (70.5% - 86/122), with a variable age range between two months to five years and an average weight of 25kg.

In a technical visit to the properties from July to October 2017, an evaluation form of the general characteristics of the creation (type of creation, degree of technification, origin of the animals and sanitary management) was completed through 15 objective questions (2020 Mazzinghy CL, Almeida KS, Castro RS, Veschi JLA, Silva MAGS. Maedi-Visna em ovinos - revisão de literatura. Revista Científica de Medicina Veterinária. 2014; 12 (23): 1-21.). The sheep were submitted to blood collection by puncture of the jugular vein, with a single sample per animal, which was placed in sterile tubes without anticoagulant (Vacutainer® tube) and transported under refrigeration to the Laboratory for Infectious Diseases of Animals of the Unit of Teaching and Research in Veterinary Medicine at the Federal University of Acre, Rio Branco-AC. The serum, extracted by centrifugation at 5,000 rpm at room temperature, was stored in 1.0 mL aliquots per sample and frozen at -20 ° C until serological tests were performed.

As a diagnostic method, agarose gel immunodiffusion (IDGA) was used to detect anti-MVV antibodies, using capsid p28 protein in a commercial kit (Biovetech Indústria e Comércio de Produtos Biotecnológicas LTDA, Recife, PE, Brazil), licensed by Ministry of Agriculture, Livestock and Supply (MAPA) under number 9050/2005. Positive samples were characterized by the formation of antigen-antibody precipitation lines on the gel, observed in 48 hours (2121 Gregory L, Lara MCCS, Kiraly ACM, Hasegawa MY, Rizzo H, Henriques LCS, Rossi RS, Castro RS. Pesquisa de anticorpos contra Maedi-Visna em ovinos nas microrregiões de Botucatu, Campinas, Piedade e São Paulo, estado de São Paulo. Arquivos do Instituto Biológico. 2013; 80 (1): 107-110.). The results were analyzed using descriptive statistics, through relative and absolute distribution (1818 Rouquayrol MZ, Gurgel M. Epidemiologia e Saúde. 8 ed. Rio de Janeiro: MedBook, 2017. 744p.).

Results and discussion

According to the results of the IDGA, 8.19% (10/122) of the tested sheep were reactive for Lentivirus, being these three males (30% - 3/10) and seven females (70% - 7/10), all of them breed undefined and aged between two to three years. In 80% (4/5) of the properties investigated in the municipality of Porto Acre, the presence of seropositive animals was detected. The seropositivity rate in these creations, individually, varied between 4.0 and 14.2%.

Of the properties where a focus of lentivirosis was identified, 75% (3/4) were under extensive farming systems, without a balanced diet plan and without the adoption of sanitary control measures. The introduction of animals without quarantine was practiced in all (100% - 4/4) of the creations. As for the origin of the sheep, 75% (3/4) came from commercialization with neighboring creations of the municipality itself, however, in a property (25% - 1/4), the breeders and breeders were acquired through the Strengthening Program of the Sheep Productive Chain, implemented by the government of the state of Acre in 2010.

The animals identified as seropositive did not present an evident clinical picture. It is known that LVPRs develop through a progressive immune-mediated inflammatory response, with a long incubation period and chronic evolution, restricting the clinical diagnosis and promoting the perpetuation of inapparent carriers in the herd (6), which, in turn, serve as source of infection to the others susceptible (1010 Gayo E, Polledo L, Magalde A, Balseiro A, Iglesias MJG, Martínez CP, Preziuso S, Rossi G, Marín JFG. Characterization of minimal lesions related to the presence of visna/maedi virus in the mammary gland and milk of dairy sheep. Veterinary Research. 2019; 15 (109): 1-9., 2222 Arnarson H, Pálsson UM, Gudnadóttir H, Andrésdóttir V. Maedi-visna virus persistence: Antigenic variation and latency. Comparative Immunology, Microbiology & Infectious Diseases. 2017; 55: 6-12.). Thus, the use of laboratory tests is necessary to identify the infection, segregate and dispose of animals (2323 Michiels R, Van Mael E, Quinet C, Adjadj NR, Cay AB, De Regge N. Comparative analysis of different serological and molecular tests for the detection of Small Ruminant Lentiviruses (SRLVs) in belgian sheep and goats. Viruses. 2018;10(12): 1-15.).

To detect the disease, the techniques of agarose gel immunodiffusion (IDGA), immunoenzymatic assay (ELISA) and polymerase chain reaction (PCR) are commonly used, which are frequent targets of comparative studies to determine the best diagnostic strategy (2323 Michiels R, Van Mael E, Quinet C, Adjadj NR, Cay AB, De Regge N. Comparative analysis of different serological and molecular tests for the detection of Small Ruminant Lentiviruses (SRLVs) in belgian sheep and goats. Viruses. 2018;10(12): 1-15. , 2424 Adjadj NR, Vicca J, Michiels R, Regge N. (Non-)Sense of milk testing in small ruminant Lentivirus control programs in goats. Comparative Analysis of Antibody Detection and Molecular Diagnosis in Blood and Milk. Viruses. 2019; 12(1): 18.,1313 Olech M, Murawski M, Kuzmak J. Molecular analysis of small-ruminant lentiviruses in Polish flocks reveals the existence of a novel subtype in sheep. Archives of Virology. 2019; 164 (4):1193-1198.,66 Juste RA, Villoria M, Leginagoikoa I, Minguijon EUE. Milk production losses in Latxa dairy sheep associated with small ruminant lentivirus infection. Preventive Veterinary Medicine. 2020; 176.,2525 Olech M, Osinski Z, Kuzmak J. Seroprevalence of small ruminant lentivirus (SRLV) infection in wild cervids in Poland. Preventive Veterinary Medicine. 2020; 176.). The IDGA is one of the techniques recommended by the OIE (2017), used in Brazil as a screening tool in epidemiological surveys, mainly because it has a practical and economically viable methodology (2626 Organização Internacional De Saúde Animal - OIE. Código Sanitário de Animais Terrestres. 2017. Available from: http://www.oie.int. Accessed on: 28 jan. 2019.
http://www.oie.int...
).

CAEV and MVV are considered viral prototypes of Lentivirus in goats and sheep, respectively. However, using the IDGA serological test, even using the MV28 capsid protein p28 as an antigen, seropositive animals may have been exposed to both viral agents, therefore, there is a need for molecular tests for taxonomic differentiation (1313 Olech M, Murawski M, Kuzmak J. Molecular analysis of small-ruminant lentiviruses in Polish flocks reveals the existence of a novel subtype in sheep. Archives of Virology. 2019; 164 (4):1193-1198.).

IDGA, when compared to ELISA, has good specificity, but low sensitivity, bringing further limitations to its use, given the possibility of false-negative results considering the single sample test (2323 Michiels R, Van Mael E, Quinet C, Adjadj NR, Cay AB, De Regge N. Comparative analysis of different serological and molecular tests for the detection of Small Ruminant Lentiviruses (SRLVs) in belgian sheep and goats. Viruses. 2018;10(12): 1-15.). That is, the frequency found in the study area may still be underestimated.

In general, serological methods may fail due to certain factors, such as the period of immunological window, low antibody titers, late seroconversion or intermittent seropositivity and seronegativity reactions (2727 Marinho RC, Martins GR, Souza KC, Sousa ALM, Silva STC, Nobre JA, Teixeira MFS. Duplex nested-PCR for detection of small ruminant lentiviroses. Brazilian Journal of Microbiology. 2018; 49(1): 83-92.). On the other hand, molecular techniques, such as PCR, although of high cost, show promising results, allowing the detection of Lentivirus infection before seroconversion (2424 Adjadj NR, Vicca J, Michiels R, Regge N. (Non-)Sense of milk testing in small ruminant Lentivirus control programs in goats. Comparative Analysis of Antibody Detection and Molecular Diagnosis in Blood and Milk. Viruses. 2019; 12(1): 18.,2828 Molaee V, Otarod V, Abdollahi D, Lühken G. Lentivirus Susceptibility in Iranian and German Sheep Assessed by Determination of TMEM154 E35K. Animals. 2019; 9(9): 685.).

It has been shown that the combined use of the aforementioned tests increases the sensitivity and specificity of the diagnosis, facilitating the detection of infected animals and contributing to the effectiveness of control and eradication campaigns (1111 Gomez-Lucia E, Barquero N, Domenech A. Maedi-Visna virus: current perspectives. Veterinary Medicine. 2018; 21 (9): 11-21.,2323 Michiels R, Van Mael E, Quinet C, Adjadj NR, Cay AB, De Regge N. Comparative analysis of different serological and molecular tests for the detection of Small Ruminant Lentiviruses (SRLVs) in belgian sheep and goats. Viruses. 2018;10(12): 1-15.).

VM is found throughout Europe (2929 Bojar W, Junkuszew A, Dudko P, Olech M, Olesinski Z, Gruszecki T, Kuzmiak J. Risk factors associated with small-ruminant lentiviruses in sheepfold buildings. Annals of Agricultural and Environmental Medicine. 2018; 25 (3): 383-387.). The disease-free countries are New Zealand and Australia. The prevalence is much higher in developed countries, which seems to be related to the management system (1111 Gomez-Lucia E, Barquero N, Domenech A. Maedi-Visna virus: current perspectives. Veterinary Medicine. 2018; 21 (9): 11-21.). In Brazil, the occurrence of LVPR in sheep has been the object of study in several states (2121 Gregory L, Lara MCCS, Kiraly ACM, Hasegawa MY, Rizzo H, Henriques LCS, Rossi RS, Castro RS. Pesquisa de anticorpos contra Maedi-Visna em ovinos nas microrregiões de Botucatu, Campinas, Piedade e São Paulo, estado de São Paulo. Arquivos do Instituto Biológico. 2013; 80 (1): 107-110.,3030 Abreu SRO, Castro RS, Nascimento AS, Souza MG. Produção de antígeno nucleoproteíco do vírus da Artrite-Encefalite Caprina e comparação com o do vírus maedi-visna para utilização em teste de imunodifusão em ágar gel. Pesquisa Veterinária Brasileira. 2014; 18 (2): 57-60.,1919 Alves SM, Teixeira MFS, Pinheiro RR, Alves FSF, Lima AMC, de Farias DA, Aguiar TDAF. Seroepidemiological study of maedi-visna in sheep in Ceara, Rio Grande do Norte, Paraíba and Sergipe States. Semina: Ciências Agrárias. 2018; 39(5): 2017-2028.), mainly due to the increase in sheep farming in the country and the recommendations of the Sanitary Code for Terrestrial Animals for the commercialization of small ruminants at the international level (2626 Organização Internacional De Saúde Animal - OIE. Código Sanitário de Animais Terrestres. 2017. Available from: http://www.oie.int. Accessed on: 28 jan. 2019.
http://www.oie.int...
).

Thus, national seroprevalence is low to moderate, with rates ranging between 0.1% and 7.9% (2121 Gregory L, Lara MCCS, Kiraly ACM, Hasegawa MY, Rizzo H, Henriques LCS, Rossi RS, Castro RS. Pesquisa de anticorpos contra Maedi-Visna em ovinos nas microrregiões de Botucatu, Campinas, Piedade e São Paulo, estado de São Paulo. Arquivos do Instituto Biológico. 2013; 80 (1): 107-110.,3030 Abreu SRO, Castro RS, Nascimento AS, Souza MG. Produção de antígeno nucleoproteíco do vírus da Artrite-Encefalite Caprina e comparação com o do vírus maedi-visna para utilização em teste de imunodifusão em ágar gel. Pesquisa Veterinária Brasileira. 2014; 18 (2): 57-60.,1919 Alves SM, Teixeira MFS, Pinheiro RR, Alves FSF, Lima AMC, de Farias DA, Aguiar TDAF. Seroepidemiological study of maedi-visna in sheep in Ceara, Rio Grande do Norte, Paraíba and Sergipe States. Semina: Ciências Agrárias. 2018; 39(5): 2017-2028.), with the exception of Ceará, where there was a variation between null detection at 50.43 % in different regions (3131 Almeida NC, Aprigio CJL, Silva JBA, Teixeira MFS. Ocorrência de maedi/visna vírus em ovinos reprodutores no estado do Ceará. In: Congresso Brasileiro de Medicina Veterinária, 29., 2002, Gramado. Anais... Gramado: SOVERGS, 2002. Available from: http://www.sovergs.com.br/site/conbravet2002/1517.htm. Accessed on: 20 mar. 2019.
http://www.sovergs.com.br/site/conbravet...
). In the northern region, until now, only in the states of Amazonas (1414 Lima NS. Incidência de Maedi-Visna na população de ovinos (Ovis aries) em propriedades rurais da região metropolitana de Manaus - AM. 2011. 35f. Dissertação (Mestrado em Medicina Veterinária) - Escola Superior Batista do Amazonas, Manaus, 2011.) and Tocantins (1616 Mazzinghy CL, Almeida KDS, Veschi JLA, Castro RSD, Martins NEX, Sousa MG. Frequency of antibodies against ovine Lentivirus in sheep in Colinas do Tocantins, Tocantins state, Brazil. Arquivos do Instituto Biológico. 2016; 86.) epidemiological surveys of LVPRs have been carried out, showing zero occurrence and seropositivity of 1.62%, respectively. The seropositivity observed in the city of Porto Acre - AC (8.2%) was higher than the other notifications in the national territory.

The type of breeding has a direct influence on seropositivity rates. Intensive systems increase the possibility of transmission of the pathogen through direct contact, aerosols (2929 Bojar W, Junkuszew A, Dudko P, Olech M, Olesinski Z, Gruszecki T, Kuzmiak J. Risk factors associated with small-ruminant lentiviruses in sheepfold buildings. Annals of Agricultural and Environmental Medicine. 2018; 25 (3): 383-387.) or even by breastfeeding (1010 Gayo E, Polledo L, Magalde A, Balseiro A, Iglesias MJG, Martínez CP, Preziuso S, Rossi G, Marín JFG. Characterization of minimal lesions related to the presence of visna/maedi virus in the mammary gland and milk of dairy sheep. Veterinary Research. 2019; 15 (109): 1-9.). In the municipality of Porto Acre, most properties adopt a semi-intensive or extensive management system, with low agglomeration and population density in the farms. However, these animals now have free access to childbirth residues and contaminated urogenital secretions in pastures, mainly because maternity paddocks are not routinely introduced to establishments in the region, which can increase the risk of infection (1919 Alves SM, Teixeira MFS, Pinheiro RR, Alves FSF, Lima AMC, de Farias DA, Aguiar TDAF. Seroepidemiological study of maedi-visna in sheep in Ceara, Rio Grande do Norte, Paraíba and Sergipe States. Semina: Ciências Agrárias. 2018; 39(5): 2017-2028.).

In addition, the presence of risk factors, such as failures in health management, intercurrent diseases, absence of quarantine, inefficient technical assistance, and, mainly, the lack of investment in the diagnosis of infectious diseases in sheep must also be considered (2929 Bojar W, Junkuszew A, Dudko P, Olech M, Olesinski Z, Gruszecki T, Kuzmiak J. Risk factors associated with small-ruminant lentiviruses in sheepfold buildings. Annals of Agricultural and Environmental Medicine. 2018; 25 (3): 383-387.,3232 Michiels R, Van Mael E, Quinet C, Welby S, Cay AB, De Regge N. Seroprevalence and risk factors related to small ruminant lentivirus infections in Belgian sheep and goats. Preventive Veterinary Medicine. 2018; 1 (151): 13-20.), a reality observed in the municipality of Porto Acre. This critical situation determines the introduction of infected animals, as well as the spread and perpetuation of the virus in herds.

The origin of the animals’ acquisition is also an important factor to be discussed. The emergence of LVPR in the state of Acre may be related to a governmental action to encourage small producers, which allowed the introduction of breeding stock and breeders from other states, without rigidity in sanitary control. In 2010, the State Secretariat of Agriculture and Livestock of Acre prepared and financed the Project to Strengthen the Sheep Production Chain for donation of sheep to local producers, mainly in the municipalities of Porto Acre and Cruzeiro do Sul. The guarantee offered was the purchase of lambs by a state slaughterhouse, improving the income and quality of life of families living in the countryside. However, the animals provided by the Project for the formation of the Acre herd came from Bahia and São Paulo, states in which the LVPR had already been detected in previous research in an endemic way (3333 Lombardi AL, Nogueira AHC, Feres FC, Paulo HP, Castro RS, Feitosa FLF, Cadioli FA, Peiró JR, Perri SHV, Lima VFM, Mendes LCN. Soroprevalência de Maedi-Visna em ovinos da região de Araçatuba, SP. Arquivo Brasileiro de Medicina Veterinária e Zootecnia. 2009; 61 (6): 1434-1437.,3434 Martinez PM, Costa JN, Souza TS, Costa Neto AO, Pinheiro RR. Sistema de criação de ovinos e ocorrência de anticorpos contra o vírus da Maedi-Visna na microrregião de Juazeiro, BA. Revista Brasileira de Saúde e Produção. 2010; 11(2):342-353.).

As there is no efficient treatment and the development of vaccines is not possible due to the high rate of viral mutation caused by the variety of strains in different geographical regions, discarding seropositive animals and replacing them with seronegative animals is the most efficient measure to reduce the occurrence LVPR in the herd, although economically expensive.

Thus, the practice of quarantine, as well as the cleaning and disinfection of drinking fountains and feeders, the isolation of sheep in the puerperium, the investigation of animals with respiratory problems in the last five years or recently introduced are relevant actions for the control of the disease (3535 Heinrichs R, Wilkins W, Schroeder G, Campbell J. Prevalence of Maedi-visna in Saskatchewan sheep. Canadian Veterinary Journal. 2017; 58(2):183-186. , 3636 Thomann B, Falzon LC, Bertoni G, Vogt HR, Schüpbach-Regula G, Magouras I. A census to determine the prevalence and risk factors for caprine arthritis-encephalitis virus and visna/maedi virus in the Swiss goat population. Preventive Veterinary Medicine. 2017; 137:52-58.,2727 Marinho RC, Martins GR, Souza KC, Sousa ALM, Silva STC, Nobre JA, Teixeira MFS. Duplex nested-PCR for detection of small ruminant lentiviroses. Brazilian Journal of Microbiology. 2018; 49(1): 83-92.,3737 Cecchi F, Dadousis C, Bozzi R, Fratini F, Russo C, Bandecchi P, Cantile C, Mazzei M. Genome scan for the possibility of identifying candidate resistance genes for goat lentiviral infections in the Italian Garfagnina goat breed. Tropical Animal Health and Production. 2019; 51(3):729-733.,66 Juste RA, Villoria M, Leginagoikoa I, Minguijon EUE. Milk production losses in Latxa dairy sheep associated with small ruminant lentivirus infection. Preventive Veterinary Medicine. 2020; 176.). A recent international study also deals with genome research, envisioning the possibility of identifying genes that are candidates for resistance to Lentivirus infections, which may later be a reality in the country (3838 Colussi S, Desiato R, Beltramo C, Peletto S, Modesto P, Maniaci MG, Campia V, Quasso UM, Rosati S, Bertolotti LLR, Acutis PL. A single nucleotide variant in the promoter region of the CCR5 gene increases susceptibility to arthritis encephalitis virus in goats. BMC Veterinary Research. 2019; 15(1):230.).

However, it is known that the actions of the National Health Program for Goats and Sheep (PNSCO / MAPA), which establish guidelines for the epidemiological surveillance of certain infectious diseases, are still minimal in practically the entire national territory. It is believed, then, that the restructuring of the Program, combined with constant epidemiological investigations carried out at the state and national levels, will contribute more solidly to the detection and elimination of LVPR outbreaks, improving the health of herds and stimulating the growth of the production of sheep across the country.

Conclusion

Seropositivity of sheep to MVV in the city of Porto Acre raises the possibility that the acquisition of small ruminants from other states represented a risk to sheep health and highlights the need for systematic investigations on the prevalence of LVPR and its risk factors in the state of Acre. Considering that its occurrence is inversely proportional to the consolidation of the local production chain, harmful to animal welfare and limiting market advantages, obtaining more information about the epidemiological condition of the disease promotes the development and adoption of control and prevention measures that avoid the entry of animals carrying the virus in the Acre herd.

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Publication Dates

  • Publication in this collection
    19 Aug 2020
  • Date of issue
    2020

History

  • Received
    24 June 2019
  • Accepted
    03 Mar 2020
  • Published
    16 May 2020
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