Yaba tumor poxvirus synthesis in vitro. I. Cytopathological, histochemical, and immunofluorescent studies

Risk of Monkeypox virus (MPXV) transmission through the handling and consumption of food

Monkeypox (MPX) is a zoonotic infectious disease caused by Monkeypox virus (MPXV), an enveloped DNA virus belonging to the Poxviridae family and the Orthopoxvirus genus. Since early May 2022, a growing number of human cases of Monkeypox have been reported in non-endemic countries, with no history of contact with animals imported from endemic and enzootic areas, or travel to an area where the virus usually circulated before May 2022. This qualitative risk assessment aimed to investigate the probability that MPXV transmission occurs through food during its handling and consumption. The risk assessment used "top-down" (based on epidemiological data) and "bottom-up" (following the agent through the food chain to assess the risk of foodborne transmission to human) approaches, which were combined. The "top-down" approach first concluded that bushmeat was the only food suspected as a source of contamination in recorded cases of MPXV, by contact or ingestion. The "bottom-up" approach then evaluated the chain of events required for a human to become ill after handling or consuming food. This approach involves several conditions: (i) the food must be contaminated with MPXV (naturally, by an infected handler or after contact with a contaminated surface); (ii) the food must contain viable virus when it reaches the handler or consumer; (iii) the person must be exposed to the virus and; (iv) the person must be infected after exposure. Throughout the risk assessment, some data gaps were identified and highlighted. The conclusions of the top-down and bottom-up approaches are consistent and suggest that the risk of transmission of MPXV through food is hypothetical and that such an occurrence was never reported. In case of contamination, cooking (e.g., 12 min at 70°C) could be considered effective in inactivating Poxviridae in foods. Recommendations for risk management are proposed. To our knowledge, this is the first risk assessment performed on foodborne transmission of MPXV.

Detection of human-pathogenic poxviruses

With the eradication of smallpox about 30 years ago, the identification and differentiation of other poxviruses with varying pathogenicity in humans present a challenge for diagnostic facilities. While a clinical differentiation can be demanding, electron microscopy is the fastest approach to identify poxviruses. Molecular techniques, based on specific genomic sequences, are routinely applied to identify poxvirus species and distinguish between individual virus variants. In this chapter, we present detailed protocols for both techniques and discuss questions relevant to fast and reliable diagnostics of poxviruses.

Nucleic acid synthesis in cytoplasm of Yaba monkey tumor virus-infected cells

Yaba tumor virus progeny appeared in cynomolgus monkey kidney cells at 24 h postinfection and reached a plateau at 72 h in the first cycle of replication. Viral DNA synthesis was first detected at about 3 h and reached a peak in 18 h. Maximum coating of viral DNA in infected cells occurred at 4 days postinfection. Rapidly labeled RNA was synthesized in the cytoplasm of virus-infected cells. At 6 h postinfection 7 to 10S RNA was present; this species was present in greater amount at 12 h; at 24 h a truncated peak indicated the presence of 14 to 15S as well as 7 to 10S RNA. Hybridization data indicated that the largest peak of messenger RNA synthesis occurred at 11 to 13 h postinfection and a second, slightly smaller, peak occurred at 21 to 23 h.

Growth kinetics of Yaba tumor poxvirus after in vitro adaptation to cercopithecus kidney cells

Yaba tumor poxvirus has been adapted to continuous in vitro cultivation in monolayers of cercopithecus kidney cells. At 35 C, the minimum replicative cycle, after synchronous infection of CV-1 cells with multiplicity of infection of 135 focusforming units per cell, was 35 hr; however, maximum virus yields were not obtained until 75 hr postinfection (PI). Cytoplasmic incorporation of (3)H-thymidine [viral deoxyribonucleic acid (DNA) synthesis] was detected 3 hr PI and was preceded by synthesis of nonstructural associated antigens (YS). Synthesis of YS antigens was not inhibited by the DNA inhibitor, arabinofuranosyl cytosine (ARA-C). Synthesis of at least two virion structural antigens, although not detected by immunofluorescence until 2 hr after the onset of DNA synthesis, occurred in the presence of ARA-C, indicating potential translation of these structural antigens from parental DNA. The first progeny DNA was completed by 20 hr PI but was not detected in infectious form until 35 hr PI. The maximum rate of progeny DNA completion occurred between 20 and 30 hr PI. DNA synthesis continued 45 to 50 hr PI. The adapted virus retained its oncogenicity and, like the wild type, replicated better at 35 C than at 37 C. A synthetic step associated with viral DNA synthesis appears to be temperature-sensitive.

Immunodiffusion analysis of Yaba poxvirus structural and associated antigens

Yaba poxvirus virions were extracted and purified from Rhesus monkey tumors. A saline-soluble virion fraction (Y-xp), obtained by mechanical fractionation of purified virions with an X-press, contained seven components in acrylamide gel electrophoresis; five of these components were reactive in immunodiffusion with whole virion and Y-xp antisera produced in rabbits and monkeys. The saline-insoluble residue remaining after X-press treatment was hydrolyzed with sodium dodecyl sulfate, urea, and 2-mercaptoethanol (SUM). This fraction, Y-sum, contained five components, four of which were demonstrable by immunodiffusion. There was no evidence of antigenic relationships between Y-xp and Y-sum antigens in immunodiffusion. In acrylamide gel electrophoresis, one Y-xp and one Y-sum component had similar mobilities. Y-xp but not Y-sum antisera contained viral-neutralizing antibodies. Virus-free saline extracts of Yaba tumor prepared with Genetron (YS) were essentially devoid of virion structural antigens. They failed to induce precipitating antibodies for virion antigens, were nonreactive in immunodiffusion with virion antisera, and gave low complement-fixation titers with virion antisera. Yaba virion antigens were recovered from the Genetron tumor sediment by SUM and alkaline hydrolysis. Antisera prepared to YS extracts gave a maximum of 17 precipitin lines in immunodiffusion with YS extracts; none was identified as a virion structural antigen. Saline extracts of tumor prepared without Genetron contained immunogenic amounts of 5 virion antigens and 12 to 14 associated antigens. Animals immunized with infected cell culture extracts (virus-free) formed antibodies to six to seven virion antigens. The implications of using extracts of Yaba poxvirus-infected tissues in complement-fixation tests to measure virion antibodies were discussed.

Latent virus infections in primate tissues with special reference to simian viruses

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Yaba tumor poxvirus synthesis in vitro. 3. Growth kinetics

Yohn, David S. (Roswell Park Memorial Institute, Buffalo, N.Y.), Victoria A. Haendiges, and Etienne de Harven. Yaba tumor poxvirus synthesis in vitro. III. Growth kinetics. J. Bacteriol. 91:1986-1991. 1966.-The infectious synthetic cycle of Yaba poxvirus by BSC-1 cells at 35 C is described and discussed together with related observations obtained by immunofluorescence and electron microscopy. After adsorption of virus at 25 C, at least 6 hr of incubation at 35 C was required before viral eclipse was demonstrable. Infectious progeny appeared after an additional 48 hr of incubation at 35 C. Newly synthesized virus particles were seen at 68 hr but not at 44 hr by electron microscopy. Maximal maturation occurred between 100 and 120 hr. Maximal yields were obtained from the 5th through the 8th day. The differences in kinetics between Yaba and vaccinia poxviruses, as described for the latter in the literature, are discussed. Possible factors accounting for these differences are enumerated.

Yaba tumor poxvirus synthesis in vitro. II. Adsorption, inactivation, and assay studies

Yohn, David S. (Roswell Park Memorial Institute, Buffalo, N.Y.), Fanny R. Marmol, Victoria A. Haendiges, and James T. Grace, Jr. Yaba tumor poxvirus synthesis in vitro. II. Adsorption, inactivation, and assay studies. J. Bacteriol. 91:1953-1958. 1966.-Means to increase the efficiency of the Yaba tumor poxvirus assay in BSC-1 cell cultures were sought. A method was devised wherein 0.4 ml of each virus dilution was layered onto BSC-1 cells in 80-mm Leighton tubes and permitted to adsorb at 25 C for 18 hr prior to incubation at 35 C. The diluent found most reliable was medium 199 containing 50% bovine amniotic fluid adjusted to 2.0 mm calcium and 1.0 mm magnesium at pH 7.0. These modifications yielded highly reproducible titrations with a greater than twofold increase in assay sensitivity. Irreversible adsorption of Yaba virus by BSC-1 cells proceeds comparatively slowly at 25 to 33 C. Although the process is more rapid at 35 or 37 C, the increased thermal lability of the virus at these temperatures results in lower titers than with virus adsorbed at 25 C for longer periods of time. Yaba poxvirus appears to be 5 to 10 times more sensitive to thermal inactivation than vaccinia poxvirus.