Aracatuba Virus: A Vaccinialike Virus Associated With Infection in Humans and Cattle

Giliane de Souza Trindade, Flávio Guimarães da Fonseca, João Trindade Marques, Maurício Lacerda Nogueira, Luiz Claudio Nogueira Mendes, Alexandre Secorun Borges, Juliana Regina Peiró, Edviges Maristela Pituco, Cláudio Antônio Bonjardim, Paulo César Peregrino Ferreira, Erna Geessien Kroon

Disclosures

Emerging Infectious Diseases. 2003;9(2) 

In This Article

Discussion

In Brazil, few studies have been conducted on the existence and circulation of poxviruses in the wild. In recent years, however, a growing number of poxvirus isolates have been obtained from samples from wild and domestic animals as well as humans; some of these viruses have caused cowpoxlike diseases in both animals and humans.[6,14,19] All of these reports have shown that such viruses were related to VACV, which raises the question of whether populations of VACV are actively and widely circulating in the country among wild or domestic animal hosts. If so, such an event is similar to the history of the buffalopox virus in India and Southeast Asia. Until recently, that virus was considered an exclusive case of VACV being able to adapt to long-term survival in nature.[20]

In this context, we isolated a novel virus, Araçatuba virus, from one of these cases of cowpoxlike diseases. The infection affected a herd of milking cows as well as their milker, in a rural area of the state of São Paulo, Brazil. Overall, our results suggest that the isolated virus is a VACV variant. Sequencing of conserved and nonconserved genes from poxviruses, such as TK, VGF, and HA, respectively, has been used for the classification of unknown poxvirus isolates.[6,14,19] In the case of Araçatuba virus, phylogenetic trees designed from the nucleotide sequences of these genes indicate clearly that the virus belongs to the VACV subgroup like other orthopoxviruses isolated in Brazil during the 1960s and 1970s, the BeAn 58058 and Cotia viruses.[6,19,30] This proposition is strengthened by RFLP analysis of the Araçatuba virus ATI homologous gene. This strategy has also been widely used for poxvirus taxonomy studies.[25,26] Although the Araçatuba virus ATI pattern is not identical to the VACV-WR pattern, the virus fits on the VACV subgroup, and the pattern differs decidedly from the CPXV ATI pattern. Such differentiation is important because CPXV was the most obvious candidate to be the agent of such diseases. The Cantagalo virus ATI gene was characterized only at protein level and showed the same pattern of bands as the VACV strains.[14]

For now, the discussion about the probable origin of Araçatuba virus, as well as other VACV isolated from animals and people in the country, is purely speculative. Araçatuba virus could be another vaccinialike strain or could represent the spread of Cantagalo virus. A logical assumption is to associate these viruses with variola vaccine stocks that may have escaped to the wild when the vaccination program was taking place in the 1970s and early 1980s. However, identifying the origin of those isolated VACV is difficult since many different samples, such as VACV-Lister, VACV-WR (Brazilian Health Ministry, pers. comm.), VACV-IOC,[14] and even mixtures of different samples were used during the smallpox elimination campaign in Brazil. Researchers have proposed that at least one of the isolates, the Cantagalo virus, may have been derived from VACV-IOC.[14] However, this finding is based on the nucleotide sequence of a single gene, and this issue is still a subject of some debate. Nevertheless, the Araçatuba virus HA nucleotide sequence revealed an interesting similarity with that of the same gene from Cantagalo virus, particularly at a signature sequence used to trace back the possible origin of this virus. Also of note, the Cantagalo virus was isolated in the city of Cantagalo (Rio de Janeiro state), about 850 km east of Araçatuba city. Moreover, a similar genetic feature of the HA gene was also detected in yet another cowpoxlike virus isolated from persons in the city of Muriaé (state of Minas Gerais), 800 km north of Araçatuba (data not published).

From the northern border at the Amazon region to the countryside of southeastern Brazil, an alarming number of genetically related vaccinialike viruses have been isolated from infected animals and humans. This fact clearly points to the existence and wide circulation of established, active VACV isolates in the vast wild and rural areas of Brazil. Whether the number of VACV infections has recently increased or whether only now they are being reported is difficult to determine. Nevertheless, the isolation of Araçatuba virus, together with other recently isolated viruses, was sufficient to trigger an alert by the Public Health Bureau in at least one of São Paulo's neighboring states (Minas Gerais). How these viruses managed to persist in nature so long after the end of smallpox vaccination is a matter of speculation, but we think that they established circulation in some unknown wild hosts and were eventually transmitted to cattle and humans when they came in contact with populations of wild animals because of agricultural expansion.

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