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


Emerging Infectious Diseases. 2003;9(2) 

In This Article

Abstract and Introduction

We describe a vaccinialike virus, Araçatuba virus, associated with a cowpoxlike outbreak in a dairy herd and a related case of human infection. Diagnosis was based on virus growth characteristics, electron microscopy, and molecular biology techniques. Molecular characterization of the virus was done by using polymerase chain reaction amplification, cloning, and DNA sequencing of conserved orthopoxvirus genes such as the vaccinia growth factor (VGF), thymidine kinase (TK), and hemagglutinin. We used VGF-homologous and TK gene nucleotide sequences to construct a phylogenetic tree for comparison with other poxviruses. Gene sequences showed 99% homology with vaccinia virus genes and were clustered together with the isolated virus in the phylogenetic tree. Araçatuba virus is very similar to Cantagalo virus, showing the same signature deletion in the gene. Araçatuba virus could be a novel vaccinialike virus or could represent the spread of Cantagalo virus.

The poxviruses comprise a family of large DNA viruses capable of infecting vertebrate and invertebrate hosts.[1] Viruses from this family have caused naturally occurring or introduced infections in all populated continents.[2] In Brazil, as in other parts of South America, little is known about the occurrence and circulation of poxvirus in the wild.[3,4,5,6] After the worldwide elimination of smallpox in the 1970s, a few reports of poxvirus isolation in South America have been published, including scattered reports of parapoxvirus outbreaks in sheep and goat herds and virus isolation from wild or captive animals.[7,8] The existence of mousepox outbreaks in animal facilities is also known, but most cases remain unpublished.

In recent years, however, many cases of unidentified diseases in dairy cattle with similar pathology have been reported in rural areas of Brazil, and some human infections have been associated with these illnesses in herds. Such diseases, characterized by the appearance of nodular and pustular lesions on bovine teats, are frequently related to viral infections such as bovine herpes mammillitis, pseudocowpox, and cowpox infections.[9,10,11,12]

After clinical and initial laboratory analysis, cowpox virus (CPXV) was considered to be the obvious etiologic agent causing this human and cattle infection. CPXV (genus Orthopoxvirus) is the causative agent of localized and painful vesicular lesions. The virus is believed to persist in wild host reservoirs (including mammals, birds, and rodents), cattle, zoo animals, and domestic animals, including cats in parts of Europe and Asia. Contact of these reservoirs with susceptible animals and people can trigger the onset of disease.[13,14] When humans are affected, the lesions occur on the hands and sometimes on the arms, usually followed by axillary adenopathy.[15] However, CPXV isolation has not been reported from cattle or humans in Brazil, which led investigators to consider the possibility that infections were caused by vaccinia virus (VACV), since VACV was used as a live smallpox vaccine throughout the country until the late 1970s.

The occurrence of VACV-infected animals (domestic or wild species) is believed to be a result of contact with people recently vaccinated against smallpox. In fact, during mass smallpox vaccination campaigns, VACV infections were occasionally transmitted from the vesicular lesion on the vaccinee to domestic animals, usually cattle. In turn, infected animals transmitted VACV to susceptible people.[14,16,17] Such infections were shown to be reproducible in experimental conditions.[18]

Vaccinialike viruses have been isolated from the wild in Brazil; at least one of these viruses, the Cantagalo virus, was specifically obtained from infected cattle and humans after an outbreak of a cowpoxlike disease.[6,14,19] These facts indicate the long-term establishment and active circulation of different vaccinialike viruses in the wild in South America, similar to the well-documented establishment of buffalopox virus in India.[19,20]

We describe the isolation and characterization of a vaccinialike strain linked to a cowpoxlike outbreak affecting a dairy herd and associated with human infection; a similar outbreak attributed to Cantagalo virus infection was recently described.[14] The virus reported here, named Araçatuba virus, was readily identified as a poxvirus by conventional methods, including characterization of pock morphology on the chorioallantoic membrane of chick embryos and electronic microscopy, which allows a quick differentiation between CPXV, pseudocowpox virus, and herpesvirus. However, such techniques do not differentiate between closely related viruses such as CPXV and VACV. To obtain accurate phylogenetic information, we detected poxvirus-conserved genes, such as thymidine kinase (TK), vaccinia growth factor (VGF), and hemagglutinin (HA), in the genome of Araçatuba virus using polymerase chain reaction (PCR). These genes were sequenced and the data used to generate phylogenetic trees. We also analyzed the A-type gene (ATI) based on restriction length polymorphism, which is a phylogenetic tool used to differentiate and classify orthopoxviruses.[13] Based on these techniques, Araçatuba virus was shown to be similar to VACV-Western Reserve (WR) strain, the prototype member of the poxvirus family and the Orthopoxvirus genus. In addition, in relation to the HA gene, Araçatuba virus was very similar to Cantagalo virus, showing the same signature deletion in the gene. Such findings specifically point to the ubiquity of VACV circulating in the wild in Brazil as well as to the public health problems that may arise from the presence of this virus.