Epizootiology, laboratory and virulence analyses during the emergency phase of the African swine fever eradication program in Brazil in 1978: a historic account

Abstract

After the first African swine fever (ASF) outbreak occurred in Brazil in 1978, an official laboratory for ASF diagnosis (ASFDL) was established. The current work reviews the efforts of the laboratory team to define an ASF diagnosis during the emergency phase of the ASF Eradication Program. From June to December 1978, 3,803 samples of pig tissue, blood and serum were analyzed. ASFDL first isolated the ASF virus (ASFV) from pig tissue samples from the Teresópolis municipality in the Brazilian state of Rio de Janeiro. During the first two months, ASFV was isolated from 130 of 320 (40.62%) pig samples analyzed by haemadsorption (HAD), indicating that the outbreak had reached 96 of 214 municipalities surveyed throughout the country in that period. The distribution of positive ASFV samples indicated the potential route of virus dispersal. Because of the rapidity of the actions implemented against ASF, the number of ASFV positive samples decreased from 48.36% in June to 33.53% in July, and then to 0% in August 1978. In parallel, ASFV antibody detection increased from 17.89% in June to 52.04% in August 1978. In the state of Paraná, a comparison of ASFV isolates with descriptions of the disease, and a rapid decrease in mortality rates suggested the occurrence of a low or moderate virulence ASFV strain. Establishment of ASFDL was crucial for the program, which eradicated ASFV from the country within six years of the first outbreak. Advances in cellular and molecular biology corroborated pioneer studies regarding ASFV virulence, and have highlighted the importance of establishing and maintaining secure measures to prevent ASFV reintroduction to the country. Information on virulence heterogeneity in ASFV populations during outbreaks provided a paramount tool for the adoption of eradication best practices. país, nos primeiros dois meses, de 320 amostras analisadas, 130 (40.62%) foram positivas pelo teste de hemadsorção o que sugere que a infecção com VPSA alcançou suínos em 96 dos 214 municípios analisados no período. A distribuição dos isolamentos do vírus no país mostrou uma possível rota de dispersão viral. Devido à rapidez das ações de eliminação dos focos, o número de amostras positivas caiu de 48,36% em Junho para 33,53% em Julho até nenhuma em Agosto, de 1978. Paralelamente, a detecção de anticorpos aumentou de 17,89% a 52,04% de Junho para Agosto de 1978. Os isolamentos do vírus pela técnica de hemadsorção (HAD) quando comparados com a descrição da doença e o forte declínio na taxa de mortalidade no Estado do Paraná sugeriram a ocorrência de cepas virais de VPSA de baixa a moderada virulência. A implantação do LDPSA foi crucial para o programa que assegurou a erradicação do VPSA em todo país após seis anos do primeiro surto. Os avanços na biologia celular e molecular corroboraram as suposições dos estudos pioneiros sobre a virulência viral e alertam para a importância de se estabelecer e manter medidas de segurança para prevenir a reintrodução do VPSA no país. A informação sobre heterogeneidade na virulência...

African Swine Fever: Fast and Furious or Slow and Steady?

“…However, this might explain the differences in mortality between experimental and field settings, as direct contact to blood is more likely in experimental settings than in the field. Until now, the role of chronically infected animals within the spread of ASF in wild boar is highly disputed [58,59,60,94]. If animals that have recovered from ASF were still able to spread the disease, this could certainly influence the spreading of ASF and its speed.…”

“…However, the course of an ASF epidemic in wild boar may last for a long time, regardless of the virulence of the circulating strain [1,92,93]. In Brazil, where the virus strain circulating in domestic pigs was characterized as low virulent, it took several years until the disease had been eradicated [94]. In this case, the epidemic spread over the entire country and also affected several neighboring countries.…”

African Swine Fever: Lessons to Learn From Past Eradication Experiences. A Systematic Review

“…During the emergency period (1978)(1979), a federal level working group and an official laboratory for ASF diagnosis (ASFDL) were set up. The ASFDL was a paramount tool for the adoption of best eradication practices, providing information on ASFV heterogeneity (low-and highvirulence strains) (48). During the emergency period, all the actions were integrated between the Ministry of Agriculture, the Ministry of the Army, and the Military police.…”

“…In November 1980, a vast national program was launched which aimed at eradicating ASF and controlling CSF simultaneously in a joint effort. The program's activities had characteristics in common with the previous phase, with exception of vaccination against CSF (48). The technical and financial support for the program (from 1980 to 1987) and the establishment of diagnostic facilities for ASF surveillance were only possible jointly with the Federal University of Río de Janeiro, the financial support by the FAO and OIE and the Ministry of Agriculture (46,49).…”

“…An activity named "garbage operation" within the eradication campaign was noteworthy; this was based on the registration and elimination of pigs kept in public garbage plants and slums performed with the help of the Ministry of Health and the Military Police (46)(47)(48). This action was responsible for the end of the transmission cycle of the disease within nonindustrialized breeding programs (46,47).…”