MicrobiologyBytes

At the 64th gathering of the World Health Assembly in May 2011, a majority of delegates reaffirmed the view that the remaining stocks of variola virus, the causative agent of smallpox, should be destroyed. But consideration of precisely when that action should be taken was postponed for several years pending completion of crucial research addressing the development and assessment of tools for the treatment and control of the disease should it ever reoccur. This agenda of research includes the development and testing of vaccines and therapeutics, at the heart of which involves understanding the mechanisms that govern variola’s virulence and its capability to evade host defenses. But how can these questions be addressed when naturally occurring disease has been eliminated and no satisfactory animal model exists?

In the absence of smallpox, human infections with monkeypox virus constitute the most significant communicable Orthopoxvirus-associated illnesses extant in the world today. Monkeypox is not a direct research-proxy or substitute for smallpox (monkeypox is a zoonosis that can affect a broad range of animal taxa, whereas smallpox was an exclusive disease of humans) but vaccines and therapies developed for smallpox may be useful for the prevention and treatment of monkeypox, and many of the cornerstones of pathogenesis and immunomodulation for both variola and monkeypox probably emanate from conserved homologous processes. Both variola and monkeypox viruses are considered threat agents that could be used unlawfully for acts of bioterrorism. With monkeypox, there is the added question of its persistence in nature, and its potential for expansion in a world that is now more than 30 years without smallpox. A significant expansion of monkeypox in the world today could pose many of the same challenges as a resurgence of smallpox.

Outbreaks of human monkeypox after cessation of smallpox vaccination. Trends Microbiol. 10 Jan 2012
The recent observation of a surge in human monkeypox in the Democratic Republic of the Congo (DRC) prompts the question of whether cessation of smallpox vaccination is driving the phenomenon, and if so, why is re-emergence not universal throughout the historic geographic range of the virus? Research addressing the virus’s mechanisms for immune evasion and induction, as well as that directed at elucidating the genes involved in pathogenesis in different viral lineages (West African vs Congo Basin), provide insights to help explain why emergence appears to be geographically limited. Novel vaccines offer one solution to curtail the spread of this disease.

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Cowpox virus (CPXV) is one of the earliest described members of the genus Orthopoxvirus (OPV). Historically, researchers referred to the ailment known as cowpox and even suggested that it could provide immunity against smallpox. It was Edward Jenner’s publications in 1798 and 1799 which provided the first scientific description of vaccination by detailing the efficacy of CPXV “scarification” in inducing protective immunity against challenge with variola (smallpox) virus (VARV). The common name “cowpox virus” refers to the association with pustular lesions on the teats of cows and historic zoonotic transmission of this disease to humans (milkers) through contact with infected cows. Human infections are generally mild and self-limiting with localized skin lesions healing after 3–4 weeks, however, systemic involvement and fatal outcome have been reported in immunocompromised individuals.

New analysis shows that the smallpox vaccine is known to have originated in the United Kingdom, however the vaccine strains were most closely allied to CPXV isolates from Russia and from Finland. The most likely scenario is that most of the commercially produced smallpox vaccines were not made from the original Jenner strain, but instead from isolates found in other regions of Europe.

Chasing Jenner’s Vaccine: Revisiting Cowpox Virus Classification. (2011) PLoS ONE 6(8): e23086. doi:10.1371/journal.pone.0023086
Cowpox virus (CPXV) is described as the source of the first vaccine used to prevent the onset and spread of an infectious disease. It is one of the earliest described members of the genus Orthopoxvirus, which includes the viruses that cause smallpox and monkeypox in humans. Both the historic and current literature describe “cowpox” as a disease with a single etiologic agent. Genotypic data presented herein indicate that CPXV is not a single species, but a composite of several (up to 5) species that can infect cows, humans, and other animals. The practice of naming agents after the host in which the resultant disease manifests obfuscates the true taxonomic relationships of “cowpox” isolates. These data support the elevation of as many as four new species within the traditional “cowpox” group and suggest that both wild and modern vaccine strains of Vaccinia virus are most closely related to CPXV of continental Europe rather than the United Kingdom, the homeland of the vaccine.

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It seems like only yesterday we were on the verge of international agreement to destroy all remaing laboratory stocks of smallpox (variola) virus. So it comes as something of a surprise to find people infecting monkeys with smallpox to study the pathogenesis of the disease. Such studies significantly advance our understanding of variola pathogenesis in primates and could help development of new antiviral drugs, improved bioterrorism countermeasures, and suggest new potential targets for therapeutic intervention in humans.

But is it a good idea?

Progression of Pathogenic Events in Cynomolgus Macaques Infected with Variola Virus. (2011) PLoS ONE 6(10): e24832. doi:10.1371/journal.pone.0024832
Smallpox, caused by variola virus (VARV), is a devastating human disease that affected millions worldwide until the virus was eradicated in the 1970 s. Subsequent cessation of vaccination has resulted in an immunologically naive human population that would be at risk should VARV be used as an agent of bioterrorism. The development of antivirals and improved vaccines to counter this threat would be facilitated by the development of animal models using authentic VARV. Towards this end, cynomolgus macaques were identified as adequate hosts for VARV, developing ordinary or hemorrhagic smallpox in a dose-dependent fashion. To further refine this model, we performed a serial sampling study on macaques exposed to doses of VARV strain Harper calibrated to induce ordinary or hemorrhagic disease. Several key differences were noted between these models. In the ordinary smallpox model, lymphoid and myeloid hyperplasias were consistently found whereas lymphocytolysis and hematopoietic necrosis developed in hemorrhagic smallpox. Viral antigen accumulation, as assessed immunohistochemically, was mild and transient in the ordinary smallpox model. In contrast, in the hemorrhagic model antigen distribution was widespread and included tissues and cells not involved in the ordinary model. Hemorrhagic smallpox developed only in the presence of secondary bacterial infections – an observation also commonly noted in historical reports of human smallpox. Together, our results support the macaque model as an excellent surrogate for human smallpox in terms of disease onset, acute disease course, and gross and histopathological lesions.

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Ground zero for vaccinology is Edward Jenner’s home in Berkeley, England. Here Edward Jenner worked, studied, and practiced as a country doctor – and later dominated a decade of my life! Jenner knew that poets talked about the nice complexions of milkmaids, and he heard a milkmaid say she was immune to smallpox because she had acquired cowpox. He came to believe in the protective effects of cowpox after careful review of the experiences of milkmaids during smallpox outbreaks. He spent a dozen years observing before he experimented with the transfer of cowpox from a lesion on the hand of Sarah Nelms, a milkmaid, to 8-year-old James Phipps, the son of a local laborer, in May 1796. Although Jenner had no concept of viruses, immune systems, or vaccinology, he used science to help imitate what he saw happening in nature.

I visited the museum several years ago and was impressed. If you ever have the chance – go there.

Edward Jenner Museum. Emerg Infect Dis Volume 17, Number 4–April 2011 doi: 10.3201/eid1704.101680

Related:

• A dose of the pox: An interactive tutorial that steps you through the discovery & ultimate eradication of smallpox using a series of questions. At each step, information & images are provided to help broaden ones appreciation of this scientific feat.

In 2011 the World Health Organization (WHO) plans to announce its recommendation regarding the final destruction of all known remaining smallpox virus stockpiles. Smallpox, an ancient human scourge of unparalleled destructive importance throughout most of recorded human history, is believed to have emerged in the Middle East some 6,000–10,000 years ago from either camelpox or the gerbil-specific taterapox. It holds a status as one of the great killers in all human history, having produced the horrific deaths of up to 500 million persons in just the 20th century alone. At first glance, the answer to this conundrum – whether or not smallpox should be forever relegated to the autoclave of extinction – might seem an easy one. Beaten back by the Jenner vaccine first proposed in 1796, smallpox was finally declared eradicated in 1980, in one of the most profound public health achievements in human history. Since that time, WHO has made it generally known that they would like to see the elimination of all remaining variola stockpiles and made the United States and Russia the repository for all remaining stocks. At the 60th Annual World Health Assembly in 2007, the organization postponed the final decision for any recommended destruction deadline until their next meeting in 2011.

Should Remaining Stockpiles of Smallpox Virus (Variola) Be Destroyed? Emerging Infectious Diseases 17(4) April 2011

“Twenty miles south-east of Novosibirsk, in Siberia, several dozen concrete buildings have been erected outside the town of Koltsovo. The settlement is ringed with triple rows of barbed wire fences. Video cameras and motion sensors monitor any activity near the wires while soldiers from an elite Russian army unit patrol its perimeter.
This is Russia’s State Research Centre of Virology and Biotechnology – or Vector, as it is usually known. Frozen in winter, when temperatures plunge below -30^oC, and then scorched in summer, when the heat routinely rises above 30^oC, the place is as unwelcoming as you could imagine. Given its name, location and a high-security protection, Vector would make an ideal setting for a James Bond film.
This would be a fitting accolade, for Vector contains a number of unsettling scientific secrets, with the most sinister being housed in bio-containment laboratory P-4, in Building 6. Here a small storage plant, chilled by liquid nitrogen, holds phials of one of the deadliest pathogens known to medical science: the smallpox virus…”

Read more: Smallpox virus: crunch time for the fate of a global killer | The Observer

Should we destroy the remaining laboratory stocks of smallpox virus?

Now that the 20th century has passed into the domain of history books, we can retrospectively begin to assess the relative contributions that the many advances in the realm of infectious disease have actually made to public health in general. At the top of this virtuous list will surely be the discovery of antibiotics in the 1930s and the use of vaccination to eradicate smallpox as an extant human disease in the 1960s and 1970s. As clearly pointed out in a recent book by D. A. Henderson, one of the leaders of the global smallpox eradication program, this task of ridding Homo sapiens from the curse of this ancestral disease was neither easy nor without controversy. In fact, the history of the many consequences of smallpox on humankind reads like a long litany of human misery and calamitous events, but is juxtaposed with the more noble accomplishments that began with the discovery of vaccination by Jenner in 1798 and culminated with the World Health Organization (WHO) certifying the world free of smallpox in 1980. With this singular accomplishment, as many as 60–100 million individuals who would have been predicted to die of smallpox have been spared from a truly gruesome death. Nevertheless, the narrative of smallpox did not stop with its eradication as a pandemic human disease. Instead, we find ourselves still wrestling with an issue that intermingles public health policy, philosophy, national security, and bioterrorism, and affects our perceptions of research ethics with extreme pathogens in general. It boils down to a not-so-simple question: What exactly should the Victor do with the Vanquished?

Killing a Killer: What Next for Smallpox? 2010 PLoS Pathog 6(1): e1000727. doi:10.1371/journal.ppat.1000727

Related:

• W.H.O. ducks smallpox decision (again)

Human disease attributable to variola virus (VARV), the etiologic agent of smallpox, has been reported in human populations for more than 2,000 years. VARV is unique among orthopoxviruses in that it is an exclusively human pathogen. Because it has a large, slowly evolving DNA genome, researchers were able to construct a phylogeny of VARV by analyzing single nucleotide polymorphisms (SNPs) from genome sequences of 47 VARV isolates with broad geographic distributions. The results reveal two primary VARV clades, which are likely to have diverged from an ancestral African rodent-borne variola-like virus either 16,000 or 68,000 years before present (YBP), depending on which historical records (East Asian or African) are used to calibrate the molecular clock. One primary clade was represented by the Asian VARV major strains, the more clinically severe form of smallpox, which spread from Asia either 400 or 1,600 YBP. The other primary clade included both alastrim minor, a phenotypically mild smallpox described from the Americas, and isolates from West Africa. This clade diverged from an ancestral VARV either 1,400 or 6,300 YBP.
Observations of smallpox-typical skin rashes on Egyptian mummies dating from 1100 to 1580 B.C. gave credibility to theories that ancient Egypt was an early (and perhaps the earliest) smallpox endemic region. However, smallpox researchers noted that “The most striking thing about smallpox is its absence from the books of the Old and New Testaments, and also from the literature of the Greeks and Romans. Such a serious disease as variola major is very unlikely to have escaped a description by Hippocrates if it existed.” Historical records from Asia describe evidence of smallpox-like disease in medical writings from ancient China (1122 B.C.) and India (as early as 1500 B.C.). The earliest unmistakable description of smallpox first appears in the 4th century A.D. in China, the 7th century A.D. in India and the Mediterranean, and the 10th century A.D. in southwestern Asia. These early Asian descriptions could indicate that pandemic smallpox originated in East Asia. Sequence analysis indicates that divergence between VARV and rodent poxviruses occurred from 16,000 YBP to 68,000 YBP, and that VARV seems to have evolved from a pathogen of African rodents and subsequently spread out of Africa.
On the origin of smallpox: Correlating variola phylogenics with historical smallpox records
PNAS USA 2007 104:15787-15792

What does this all mean?

• In spite of concerns about bioterrorism, smallpox is no longer a major human pathogen, but understanding the origin of this disease, which has been of major importance for most of human history, offers glimpses into how we might rapidly understand new emerging diseases as they appear.
• For a long time it has been generally believed the the most probable origin for smallpox virus was in Asia, but as with yellow fever and HIV, this new research seems to show that smallpox originally came out of Africa.