Serological and molecular evidence of hepatitis E virus in swine in Brazil
Introduction
Hepatitis E virus (HEV) is a non-enveloped, single-stranded positive-sense RNA virus that is a member of the family Herpesviridae (Emerson et al., 2004). Isolates of HEV can be divided into four genotypes principally characterized by geographic distribution, host range and pattern of infection. Despite differences in nucleotide sequences, genotypes cannot be distinguished serologically, and epitopes are cross-reactive (Li et al., 2005a). Genotype 1 is primarily associated with human infections in Asia and Africa, where it has been responsible for large waterborne outbreaks. Caron et al. (2006) identified genotype 1 in a pig in Cambodia, representing the first and only animal isolate of this genotype. Genotype 2 was first identified in a single patient isolate obtained from a feces sample collected during an outbreak of non-A, non-B hepatitis in Mexico in 1986 (Huang et al., 1992). Recently, isolates from individuals in Africa have also been classified as this genotype (Nicand et al., 2005).
Molecular studies have reported genetic relationships between porcine and human isolates belonging to genotypes 3 or 4. These data suggest that swine represent a potential natural reservoir for the virus in areas not previously considered endemic, such as the United States, Europe, Canada, Mexico, New Zealand, South Korea and Japan, (Meng et al., 1997, van der Poel et al., 2001, Choi et al., 2003, Banks et al., 2004, Cooper et al., 2005, Inoue et al., 2006, Jung et al., 2006).
A porcine HEV strain recently isolated in Argentina (Munne et al., 2006b) presented a high degree of nucleotide sequence similarity to human HEV strains identified in sporadic cases previously reported in the same country (Schlauder et al., 2000, Munne et al., 2006b). In Brazil, anti-HEV antibodies have been detected in a significant proportion of healthy individuals, although no serologically confirmed acute cases of HEV infection have been documented (Souto et al., 1997, de Paula et al., 2001, Trinta et al., 2001, Santos et al., 2002, Lyra et al., 2005).
A retrospective study of the prevalence of HEV infection, based on the identification of immunoglobulin (Ig) G anti-HEV antibodies, was conducted in various animal species and in pig handlers in order to ascertain whether animal reservoirs for HEV exist in Brazil (Vitral et al., 2005). The authors also evaluated a large collection of serum specimens from pigs of different ages in order to determine anti-HEV status. The results demonstrated that most animal species, especially swine, had anti-HEV antibodies. They found that, within this Brazilian pig population, seroconversion was nearly universal by the age of 15 weeks. Another study of HEV seroprevalence carried out in a swine herd in Central-West Brazil also revealed a high prevalence of HEV (Guimarães et al., 2005).
However, to date, there have been no studies attempting to identify and characterize the HEV genome in Brazilian swine with active HEV infection. Here, we report the results of two studies conducted in swine herds in the South-East and Central-West regions of Brazil. Natural infection of swine with HEV was investigated, and the phylogenetic relationships of porcine HEV isolates were determined and compared to those of isolates described in the literature.
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Study design
The study design was in accordance with the protocol approved by the Institutional Committee for Ethics in the Use of Research Animals (CEUA-Fiocruz: PO 0132/01) and followed the regulations established in the Guide for Care and Use of Laboratory Animals published in 1996 by the US National Institutes of Health National Research Council.
The studies were carried out in swine herds located in two different regions of Brazil. Study 1 was conducted in a commercial herd in the municipal district of
Seroconversion of piglets to anti-HEV
Fig. 1 shows the median specific IgG antibody levels observed in piglets in the South-East of Brazil (study 1) monitored from birth to 22 weeks of age. All of the serum samples collected immediately after delivery from the 26 colostrum-deprived newborn piglets were negative for anti-HEV antibodies. After 24 h of continuous colostrum uptake, anti-HEV antibodies had been passively transferred to the majority of animals (24/26; 92.3%), as evidenced by the elevated antibody titres seen in the serum
Discussion
Autochthonous cases of HEV infection have been documented in several countries where the virus is not endemic, such as the United States, Spain and Argentina (Schlauder et al., 1998, Pina et al., 2000, Munne et al., 2006a). Remarkably, such cases have been associated with genotype 3 HEV strains that are closely related to those isolated from local pigs. This fact corroborates the hypothesis that swine represent a potentially significant reservoir for HEV and a potential source of zoonotic
Conflict of interest statement
None of the authors of this paper has a financial or personal relationship with other people or organizations that could inappropriately influence or bias the content of the paper.
Acknowledgments
The authors wish to thank the commercial herd owners and their employees for assistance provided, as well as Dr. Janice Ciacci-Zanella of Embrapa Suínos e Aves who kindly performed the PCV-2 PCR assays.
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