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New world cultures and civilizations
Published in Lois N. Magner, Oliver J. Kim, A History of Medicine, 2017
In a virgin soil epidemic, no members of the affected group have immunity because the entire population lacks prior experience with the disease. If all members of a community become ill simultaneously, the death toll explodes because no healthy individuals are left to provide the simplest kinds of nursing care. When parents and grandparents are sick or dead, infants and children may die from dehydration and starvation even if they do not contract the disease. Moreover, because of epidemic diseases, food supplies may be lost because no able-bodied individuals are available to harvest crops or care for domesticated animals. Of course, the New World was not a disease-free utopia, but Old World diseases like smallpox and measles were devastating to Native Americans and, therefore, served as allies in European conquest and colonization. A catastrophic, permanent demographic collapse might have occurred when the first smallpox epidemics were followed by additional waves of disease, compounded by crop failures and food shortages. Such factors could have prevented the resurgence of population that typically occurred after epidemics in the Old World.
Viruses
Published in Loretta A. Cormier, Pauline E. Jolly, The Primate Zoonoses, 2017
Loretta A. Cormier, Pauline E. Jolly
Yellow fever is a vector-borne pathogen that is endemic in the Afrotropics and the Neotropics. There is evidence that suggests that both the yellow fever virus and the Aedes aegypti mosquito vector were introduced from Africa into the Americas during the slave trade (Dobyns 1993; Kiple and Higgins 1992; Wirsing 1985). New World monkeys presumably acquired the disease from humans. Additional evidence that yellow fever was a virgin soil epidemic is that African human populations and Old World primate populations have some immunological resistance to yellow fever that is lacking among Native Americans and New World monkeys (Kiple and Higgins 1992). Although a vaccine is available, approximately 84,000–170,000 cases of yellow fever occur each year with up to 60,000 deaths, primarily in Africa (WHO 2017a). Symptoms can range from a mild febrile illness to acute liver infection and hemorrhagic disease, with a 50% mortality rate among those with acute illness (WHO 2017a).
Cholera Mortality in British India, 1817-1947
Published in Tim Dyson, India's Historical Demography, 1989
Before discussing the connection between cholera and famine in more detail, it is worth reflecting further on the possibility that the cholera that affected India in 1817-21 was a ‘virgin soil epidemic’, or at least represented the emergence of a new and more virulent strain of the disease. The way in which ‘El Tor’ cholera, originating in Indonesia, spread throughout most of South Asia in 1964-5 and displaced the ‘classic’ form of the disease,22 suggests the ease and speed with which such a transformation could occur. It is tempting, too, to go a stage further and suggest that the declining mortality from cholera was a consequence of the long-term decline in the virulence of the new strain between the 1820s and the 1960s, and thus that human intervention played very little part. It is more likely, however, that a lack of human immunity to cholera, or to this form of the disease, accounted for the exceptional scale of mortality in 1817-21, but that thereafter a certain level of ‘herd immunity’ existed and prevented epidemic mortality from reaching such heights again. Moreover, given favourable circumstances, as in Bengal in 1943, cholera remained as lethal as it had been in the middle and late nineteenth century. While bacteriological change cannot be entirely discounted, it seems unlikely that it would solely or substantially explain the overall decline in cholera mortality between 1900 and 1960.
Update on CVD 103-HgR single-dose, live oral cholera vaccine
Published in Expert Review of Vaccines, 2022
James McCarty, Lisa Bedell, Paul-Andre De Lame, David Cassie, Michael Lock, Sean Bennett, Douglas Haney
In theory, live vaccines that can be administered as a single dose and elicit rapid protection may have the potential to fill the public health gap for infants and young children in endemic regions and in emergency outbreak situations when timely deployment of vaccines is critical in ‘virgin soil’ epidemics. CVD 103-HgR has been studied in cholera endemic regions and was noted to require 1 log higher dosing to optimize serologic response, likely because of interference with intestinal vaccine replication caused by environmental enteropathy as well as previous exposures to wild-type cholera, which may interfere with replication of the vaccine bacteria in the gut [49]. In a WHO-implemented reactive mass vaccination program to control an explosive cholera epidemic in Micronesia, which documented the logistical feasibility of single-dose use of CVD 103-HgR in a reactive vaccination program, protective efficacy of the high-dose formulation (Orochol E), containing ~2–10 × 109 colony forming units (CFU), under field conditions was 79.2% (95% CI 71.9–84.6) [97], although this was a retrospective cohort study with limited information available on participants. This study contrasts with a large prospective, randomized, double-blind, placebo-controlled field trial of CVD 103-HgR performed in Indonesia, which demonstrated a protective efficacy of only 14% [98]. The study was done before the ability of cholera vaccines to elicit indirect protection was known, and the unexpectedly low incidence of cholera in the placebo population may have been secondary to inadvertent indirect protection of that group from an overall reduction in the incidence of cholera in the community secondary to mass vaccination, as well as a lack of cluster randomization [49]. Modeling studies of disease transmission have suggested that immunization may reduce cholera by up to 89% in unvaccinated people [94]. In a more recent study, CVD 103-HgR doses were evaluated in a study of Malian participants randomized to ingest a single standard dose (≥2 × 108 CFU; n = 50) or high dose (≥2 × 109 CFU; n = 50) of Vaxchora vaccine or Shanchol vaccine (n = 50) [99]. Two weeks after vaccination, the rates of seroconversion with the high-dose CVD 103-HgR vaccine (83.3%) were greater than the standard-dose vaccine (71.7%) and significantly greater than a single dose of Shanchol vaccine (56.0%; P = 0.003). While these results generated enthusiasm to evaluate the use of a high-dose formulation of Vaxchora vaccine as a potential future tool for reactive vaccination in explosive ‘virgin soil’ epidemics in developing countries [99], the clinical significance of these findings is uncertain, and prospective, randomized trials evaluating protective efficacy in endemic and epidemic situations are needed.