Calicivirus pathogenic for swine: a new serotype isolated from opaleye Girella nigricans, an ocean fish.

A new calicivirus, designated San Miguel sea lion virus type 7 (SMSV-7), was isolated from fish and produced a disease condition identical to vesicular exanthema in experimentally infected swine. Serotype SMSV-7 was also isolated from four elephant seals and one sea lion trematode, whereas a second calicivirus serotype isolated from fish proved to be SMSV-6.

Comparative resistance of San Miguel sea lion virus and vesicular exanthema of swine virus to chemical disinfectants.

Two similar calici agents, San Miguel sea lion virus (SMSV) and vesicular exanthema of swine virus (VESV) are susceptible to the virucidal activity of disinfectants of differing formulation. Ten of 12 compounds were effective against six log10 plaque forming units (PFU) of SMSV in a 2-min exposure at 4, 25 and 37 degrees C. However, only seven of these 10 SMSV-positive compounds inactivated VESV under the same conditions of temperature and time. Two compounds were not effective against SMSV in a 20-min exposure at 4 and 25 degrees C, but were effective at 37 degrees C. Two of the three compounds not effective against VESV in a 20-min exposure at 4 and 25 degrees C were also effective at 37 degrees C. The test iodophor compound inactivated SMSV completely but had only minimal inactivating activity against VESV at the three temperatures tested.

Vesicular exanthema of swine virus: isolation and serotyping of field samples.

Virus isolation was attempted from 262 field samples of vesicular material collected during the outbreaks of vesicular exanthema of swine in the U.S.A. from 1952-54. Using primary swine kidney culture, viral cytopathogenic agents were isolated from 76.3% of the samples. However, an overall recovery rate of 82.1% was obtained after samples negative in tissue culture were inoculated intradermally in susceptible swine. All vesicular exanthema of swine virus isolates were identified as serotype B51 using complement fixation and serum neutralization tests. Two isolates did not react with antisera to known vesicular agents of swine and failed to produce vesicles or clinical signs of disease upon inoculation in swine. One vesicular exanthema of swine virus isolate from tissue of equine origin was pathogenic for swine but produced limited vesiculation at the site of intradermalingual inoculation in the tongue of a pony infected experimentally. Type B51 virus was reisolated from lesions produced in the pony and the pony became seropositive for virus type B51.

Immunoelectron microscopic comparisons of caliciviruses.

Using immunoelectron microscopy, 9 serotypes of vesicular exanthema of swine virus (VESV) were compared with 5 serotypes of San Miguel sea lion virus and 7 additional calicivirus isolates from marine animals. In addition, swine caliciviruses and marine caliciviruses were compared with the vaccinal strain of feline calicivirus (FCV) F-9. Of 9 VESV types, 8 showed common antigenicity with San Miguel sea lion virus. Of 9 VESV types, 2 showed common antigenicity with FCV F-9. All 12 marine caliciviruses showed common antigenicity with VESV, but not with FCV F-9.

Prevalence of vesicular exanthema of swine antibodies among feral mammals associated with the southern California coastal zones.

Serum-neutralizing antibodies to both vesicular exanthema of swine virus (VESV) and San Miguel sea lion virus (SMSV) were found in a number of animal species having an association with the southern California coastal zones. California sea lions (Zalophus californianus) had antibodies to 9 VESV types (A48, C52, D53, E54, F54, G55, I55, J56, and K56). Fur seals (Callorhinus ursinus) and elephant seal pups (Mirounga angustirostris) were tested for antibodies to 6 VESV types and all were negative. California gray whales (Eschrichtius robustus) were tested for antibodies to 9 VESV types, and sperm whale (Physeter catodon), finback whale (Balaenoptera physalus), and sei whale (Balaenoptera borealis) were tested for 6 VESV types. Among the last 4 species, antibodies were present for each VESV type except C52, and all species were positive for antibodies to 2 or more VESV types. Feral swine from both Santa Cruz Island and Santa Catalina Island were tested and antibodies were present for 8 of 9 VESV types and all SMSV types except SMSV-4. One donkey from San Miguel Island was positive for VESV I55 and 2 were positive for SMSV-2.

Host range comparisons of five serotypes of caliciviruses.

Two new serotypes of San Miguel sea lion virus (SMSV), designated SMSV-4 and SMSV-5, were studied in vivo and in vitro. The host cell spectrums were compared with SMSV-1, SMSV-2, and vesicular exanthema of swine virus type A-48. Based on the result of these broad host spectrums, a numerical scoring system was devised for ranking each virus on the basis of its potential for infecting terrestrial mammals, including the important domestic species.

Isolation and partial characterization of a calicivirus from calves.

A calicivirus was isolated from 3 dairy calves in a herd with persistent calf respiratory tract problems. This virus, named Tillamook calicivirus, was not neutralized by 18 different calicivirus-typing serums available. The agent caused only minimal lesions in 2 experimentally exposed calves, but did establish a persistent infection with virus shedding for 45 days, after which time the experiment was terminated. Experimentally exposed swine developed clinical vesicular lesions. The possible origins, disease potential, and relationships to the exotic animal disease agent, vesicular exanthema of swine are discussed for this first calicivirus isolate of bovine origin.

Serology and virology of the bowhead whale (Balaena mysticetus L.).

Sera from four bowhead whales (Balaena mysticetus L.) were examined for the presence of specific antibodies, and tissue and swab samples from six and four animals respectively were processed for isolation of viruses and for initiation of bowhead whale cell cultures. All sera were negative for antibodies to nine serovars of Leptospira interrogans and to 21 orthomyxovirus subtypes and a paramyxovirus (Newcastle disease virus). All sera were positive, however, for neutralizing antibodies to one or more calicivirus serotypes. Two untyped adenoviruses were isolated from colon samples of two different whales, but neutralizing antibodies to the agents could not be demonstrated in any sera. Three primary bowhead whale cell cultures were derived from kidney (two cultures) and testis (one culture), from three individual whales.

Vesicular exanthema of swine.

Vesicular exanthema of swine (VES) was first recognized in 1932. At the time, eradication measures and, later, quarantine procedures were instituted and extension of the disease to surrounding farms appeared to have been prevented. Between 1932 and 1936, however, seemingly unrelated epizootics continued among swine herds being fed raw garbage. In 1936, VES disappeared only to reappear in 1939. The disease was contained within California until 1952, at which time it spread to all the major swine producing areas of the United States. The disease was eradicated in 1959, through the enforcement of laws prohibiting the feeding of raw garbage to swine. Other than the association with raw garbage, a reservoir for VES virus (VESV) was never found. In 1972, a virus isolated from California sea lions--and thus named the San Miguel sea lion virus (SMSV)--proved to be distinguishable from VESV. When SMSV was injected into swine, clinical signs of vesicular exanthema developed, leading to the conclusion that, for all practical purposes, SMSV and VESV were the same. To date, 5 species of marine mammals and 2 species of terrestrial mammals, including feral swine, have been shown to possess antibodies to 1 or more of the 4 distinct SMSV serotypes. Current evidence suggests that SMSV infections occur among both terrestrial and marine mammals inhabiting the California coastal zones. This and the practice of shipping frozen meats known to contain SMSV to mink ranches in Utah point to the possibility that domestic swine in the United States are occasionally being exposed to SMSV. Although marine mammals are a source of SMSV, the primary virus reservoir is thought to be 1 or more submammalian marine species common to the southern California coastline. Such a primary reservoir presumably is the source of a new SMSV serotypes infecting marine mammals and may have been the original source of the VESV serotypes that infected swine through the intermediary of raw garbage.

Vesicular exanthema of swine and San Miguel sea lion virus.

San Miguel sea lion virus (SMSV), recently isolated from marine mammals, and vesicular exanthema of swine virus (VESV), which caused epizootics of vesicular exanthema of swine (VES) over a period of 24 years (1932 to 1956), may be the same virus. This finding is of particular interest because the source of the original VES epizootic was never identified, swine were the only known natural host of VESV, and VESV was thought to have been eradicated. The SMSV has been shown to be enzootic in 2 species of marine mammals found off the coast of California and to cause lesions in swine that are indistinguishable from those caused by VESV. Therefore, we should be alert to recognize situations in which swine might become exposed to SMSV and to consider SMSV in differential diagnoses of vesicular conditions.

A model for vesicular exanthema virus, the prototype of the calicivirus group.

The structure of vesicular exanthema virus, the prototype member of the calicivirus group, has been studied in more detail. The RNA comprises 18% of mol. wt. of about 2.8 x 10(6), based on polyacrylamide gel electrophoresis experiments in the presence of formaldehyde. The virus contains one major polypeptide, mol. wt. 70 x 10(3) as determined by polyacrylamide gel electrophoresis and by chromatography on Sepharose 6B in the presence of 6 M-guanidine. Further evidence for the presence of a single major polypeptide was obtained by tryptic peptide analysis of 35S-methionine labelled virus. The mol. wt. of a protein oligomer produced by adjusting the pH of virus suspensions to 3.5 was c. 200 x 10(3). On the basis of these data we propose a T = 3 model for the virus capsid incorporating 180 copies of the virus protein.

A major difference in the strategy of the calici- and picornaviruses and its significance in classification.

Pig kidney (1BRS-2) cells infected with vesicular exanthema virus (VEV), a calicivirus, did not contain any large precursor polypeptides similar to those found when they were infected with foot-and-mouth disease virus (FMDV). The largest induced protein found in the VEV-infected cells had a molecular weight identical with that of the virus structural polypeptide. This difference in strategy between VEV and FMDV, taken in conjunction with the morphological and structural differences described previously, provides strong evidence that the caliciviruses should not be included in the family Picornaviridae.

Presence of a covalently linked protein on calicivirus RNA.

The infective RNA of the calicivirus, vesicular exanthema virus, has been shown to contain a protein which is apparently linked to the RNA by a covalent bond. The protein remained bound to the RNA after boiling with SDS-mercaptoethanol-urea or treating with formamide-dimethylsulphoxide but was removed by incubating with proteinase K. The mol. wt. of the protein was estimated to be about 1o X 1O(3) by electrophoresis in highly cross-linked polyacrylamide gels. The infectivity of the RNA was destroyed by removal of the protein with proteinase K.

Swine vesicular disease: comparative studies of viruses isolated from different countries.

Seven viruses isolated from outbreaks of swine vesicular disease in various countries between 1966 and 1973 were compared in pigs and infant mice. All produced a similar disease and virus excretion pattern in the pig, although the Italy/66 virus was considerably less virulent than the other viruses. The results of cross neutralization tests of convalescent pig sera and the response of 5-day-old mice to intraperitoneal inoculation indicated minor differences between some viruses. The Italy/66, Hong Kong/71 and France/73 viruses differed from each other and also from the Italy/72, England/72, Austria/73 and Poland/73 group of viruses.

Detection of swine caliciviruses by indirect immunofluorescence.

The indirect immunofluorescence test is a rapid method for detecting the presence of vesicular exanthema of swine virus or San Miguel sea lion virus in cell culture. A serological relationship exists between vesicular exanthema of swine virus and San Miguel sea lion virus, as shown by the fluorescence-positive reactions between swine antisera to vesicular exanthema of swine virus A48 and San Miguel sea lion virus type 5 and cell cultures infected with San Miguel sea lion virus types 1, 2, 3, 4 and 5 as well as vesicular exanthema of swine virus B51, C52, D53, E54, F55, G55, H55, I55, J56 and K55. The indirect immunofluorescence test detects group-specific antibody to caliciviruses in swine sera.

Vesicular exanthema of swine and San Miguel sea lion virus: experimental and field studies in otarid seals, feeding trials in swine.

The naturally occurring disease caused by San Miguel sea lion virus in fur seals was characterized by small fluid-filled vesicles 1 to 25 mm in diameter on the nonhaired portions of the flippers. Early epithelial lesions contained multifocal sites of cell lysis. The resultant microvesicles enlarged and coalesced, forming grossly visible macrovesicles. Mature vesicles progressed to involve all layers of the epithelium but did not involve the underlying dermis. Intradermal inoculation of vesicular exanthema of swine virus type A48 or San Miguel sea lion virus type 2 into otarid (fur) seal pups caused plaque-like lesions around inoculated coronary bands. These swellings regressed without rupture by 96 hours postinoculation. One seal inoculated with San Miguel sea lion virus had a linear lingual erosion at ten days postinoculation. Virus was isolated from this site and from two uninoculated sites, the tonsil and testicle. Contact controls showed no evidence of infection. Virus was isolated in low titers from some sites of inoculation and draining lymph nodes from seals infected with vesicular exanthema of swine virus. Virus was recovered more easily, in higher titers, and from more tissues, from seals infected with San Miguel sea lion virus. Inoculated seals tested after four to ten days seroconverted. Feeding swine seal tissues from the inoculation experiments resulted in seroconversion in swine which were fed tissues from seals infected with vesicular exanthema of swine virus but not in those which were fed tissues from seals infected with San Miguel sea lion virus.