Characterization of Aujeszky's disease virus isolates from South and Southeast Brazil by RFLP analysis

Caracterização de amostras do vírus da doença de Aujeszky isoladas nas regiões sul e sudeste do Brasil por RFLP

CHARACTERIZATION OF AUJESZKY'S DISEASE VIRUS ISOLATES FROM SOUTH AND SOUTHEAST BRAZIL BY RFLP ANALYSIS

Rosa Maria Piatti^1*; Alice Akimi Ikuno¹; Elenice Sequetin Cunha¹; Régia D'Ambros²; FábioGregori³; Rodrigo Martins Soares⁴ ; Adriana Cortez³; Leonardo José Richtzenhain³

¹Laboratório de Imunologia, Instituto Biológico, São Paulo, SP, Brasil. ²Cedisa, Concórdia, Santa Catarina, SC, Brasil. ³Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, SP, Brasil. ⁴Instituto de Ciências Biomédicas, Universidade de São Paulo, SP, Brasil.

Submitted: August 28, 2000; Returned to authors for corrections: January 15, 2001; Approved: June 21, 2001

ABSTRACT

The genomic DNA of thirty strains of Aujeszky's disease virus (ADV) isolated in the South and Southeast regions of Brazil from 1982 to 1996 were characterized by restriction endonuclease analysis with BamHI. Twenty seven strains were isolated from pigs, 1 from cattle, 1 from cat and 1 from dog. Using a systematization previously described, the 30 ADV strains could be classified as genomic types I (n = 2) and II (n = 28). Genomic type III was not observed. In this first study of genomic type characterization of brazilian ADV strains, we could demonstrate the occurence in Brazil of the genomic types I and II, with a large predominance of genomic type II.

Key words: Aujeszky's disease virus, swine, genomic RFLP, Brazil

INTRODUCTION

Aujeszky's Disease is spread worldwide and has been considered an important cause of economic losses in pig husbandry (19). Pigs are the only known reservoir of Aujeszky's Disease Virus (ADV), which is classified as a Suid herpesvirus-1, Herpesviridae Family, Alphaherpesvirinae Sub-Family and Varicellovirus Genus (11).

ADV is perpetuated in pig herds by alternating latency with reactivation in the host. ADV may cause mass mortality among piglets, growth losses in fattening pigs and reproductive disorders in adults. Domestic and wildlife animals may occasionally acquire the infection through contact with pigs, presenting an inevitably fatal outcome (19).

Grouping field strains of ADV into distinct serotypes has not been possible. Therefore, other markers such as cytopathogenic effect in cell cultures, pathogenicity to mice and rabbits, inactivation by UV radiation, trypsin treatment and heat sensitivity have been studied as attempts for ADV characterization (2,3,13). Genomic types of ADV strains based on Restriction Fragment Length Polymorphism (RFLP) patterns with the endonuclease BamHI were associated to viral geographic and chronological distribution in many countries (6,8).

Pig population of Brazil reaches 3.5 x 10⁶ animals and the South and Southeast regions are considered the most important producing areas. Although many ADV strains have been isolated in those regions (10,14), genomic typing of Brazilian ADV strains has never been accomplished.

The aim of the present study was to characterize the genomic types of 30 ADV strains isolated in South and Southeast Brazil, from 1982 to 1996.

MATERIALS AND METHODS

ADV strains

Thirty ADV strains isolated from 1982 to 1996 in the States of São Paulo, Paraná and Santa Catarina were studied. All strains were isolated from cerebral tissue: 27 from pigs, 1 from cattle, 1 from dog and 1 from cat. The Bartha ADV strain was used as reference and was kindly supplied by Solvay Laboratories - Campinas - São Paulo-Brazil. ADV strains were grown at 37ºC on PK-15 cells in 1,500 cm² roller bottles. After total cytopathic effect, virus suspensions were frozen at –80ºC.

Genomic DNA extraction

Viral suspensions were thawed and cellular debris removed by centrifugation at 16,000 x g for 10 minutes at 4ºC. Supernatant was layered onto a 3 mL cushion of 40% (w/v) sucrose in PBS (0.01M PO₄^— / 0.15M NaCl) pH 7.2 and centrifuged at 100,000 x g for 1 hour at 4ºC. Viral pellet was resuspended in 1 mL of TNE (Tris 0.01M, EDTA 0.001M, NaCl 0.1M) pH 8.0, 0.5% SDS and 0.2 mg proteinase K/mL and incubated for 1 hour at 56ºC. DNA was extracted by phenol-chloroform treatment as described by Sambrook et al. (15).

RFLP analysis and genomic typing

Viral genomic DNA (5 µL) was digested to completion with 5 U of BamHI according to manufacturer's instructions (Pharmacia-Sweden). Digested DNA was subjected to electrophoresis at 30 V for 18 hours at 4ºC on a 0.7% agarose gel in Tris-Borate-EDTA (45 mM Tris, 45 mM borate and 1 mM EDTA) pH 7.5.

After electrophoresis, the gel was stained with ethidium bromide (5 µg/mL) and photographed on a UV transiluminator. Genome typing of ADV strains by RFLP was performed according to Herrmann et al. (8) and Christensen (6).

Following this systematization (Fig. 1), the migration pattern of the first three fragments can be used for genomic typing of ADV strains. The genomic type II has an extra cleavage site in the fragment 2 which leds to the appearance of two new fragments 2a and 2b, located bellow the fragment 3 (not shown). The genomic type III lacks a restriction site between the fragments 2 and 9, with the appearance of a fragment (2 + 9) just bellow the fragment 1.

RESULTS AND DISCUSSION

Using the BamHI/ RFLP analysis (Fig. 2, lane B), the Bartha reference ADV strain confirmed its classification as genomic type I (8).

Among the 30 ADV strains isolated in South and Southeast Brazil over a 14 year period, 2 strains could be classified as genomic type I and 28 strains as genomic type II. Typical BamHI/RFLP patterns of genomic types I and II strains are also shown in Fig. 2, lanes I and II. The year of isolation, State of origin, affected host and genomic type of the 30 ADV strains are listed in Table 1.

Herrmann et al. (8), proposed a systematization of ADV genomic types based on the genomic BamHI RFLP analysis of a large number of ADV isolates. This systematization has been adopted by different authors around the world (1,4,5,7,9,12, 16,17,18,20).

Based on the systematization of Herrmann et al. (8) and Christensen (6), the RFLP pattern of 93.33% of the Brazilian ADV strains (28/30) could be classified as group II genomic type. Only two strains (6.66%) were classified as group I genomic type. Group II genomic type was observed in almost all the years and States studied, while group I genomic type strains were observed only in São Paulo in 1986 and 1990 (Table 1). The three VDA strains isolated from cattle, dog and cat were classified as group II genomic types and no differences among their RFLP patterns were observed.

According to Hermann et al. (8), genomic type I was found in the USA and Central Europe, while genomic type II was observed in Central Europe and Japan. Genomic type III was only observed in North Europe.

In this first study of Brazilian ADV strains genomic type characterization, we could demonstrate the occurrence of the genomic types I and II in Brazil, with a large predominance of genomic type II. The genomic type III was not observed in the 30 ADV strains studied.

RESUMO

Caracterização de amostras do vírus da doença de Aujeszky isoladas nas regiões sul e sudeste do Brasil por RFLP

O DNA genômico de 30 amostras do vírus da doença de Aujeszky (VDA), isoladas nas regiões Sul e Sudeste do Brasil no período de 1982 a 1996, foram caracterizadas por análise do perfil de restrição utilizando a enzima BamHI. Vinte e sete amostras foram isoladas de suínos, uma de bovino, uma de felino e uma de canino. Através de uma sistemática previamente descrita, as 30 amostras de VDA foram classificadas como pertencentes ao tipo genômico I (n = 2) e tipo genômico II (n = 28). O tipo genômico III não foi observado. Neste primeiro estudo de caracterização genômica de isolados de VDA do Brasil, foi possível demonstrar a ocorrência dos tipos genômicos I e II, com marcante predomínio do tipo II.

Palavras-chave: Vírus da Doença de Aujeszky, suínos, RFLP genômico, Brasil

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Publication Dates

• Publication in this collection
  12 Dec 2001
• Date of issue
  June 2001

History

• Reviewed
  15 Jan 2001
• Received
  28 Aug 2000
• Accepted
  21 June 2001