Origin and Diversity of Zoonoses Flashcards
(Jones et al., 2008)
1. what % of human pathogens and domestic animal pathogens can infect multiple host species?
- 60% human pathogens and 80% of domestic animal pathogens can infect multiple host species
Important infectious diseases of humans
1. major zoonoses?
2. emerging infectious diseases?
3. Humans are associated with…
- malaria, HIV, Cholera, Rabies, Lyme Disease, Leptospirosis, Campylobacter, E. coli, Salmonella, Schistosomiasis, Tuberculosis, Toxoplasma
- Influenza, BSE/nvCJD, SARS/MERS/SARS-CoV-2, Nipah virus, West Nile Virus, Anthrax (deliberate release), Ebola virus
- Humans are associated with a vast diversity of pathogens with unique life histories, transmission dynamics, and source of origin
(World Health Organisation)
What is zoonoses?
“diseases and infections that are naturally transmitted between vertebrate animals and humans”
what is endemic zoonoses?
present and persistent (in many places) and affect many host individuals (e.g. brucellosis, leptospirosis, salmonellosis)
what is outbreak or epidemic zoonoses?
erratic temporal or spatial disease spread (e.g. Ebola, Anthrax, rabies, Rift Valley Fever, leishmaniasis)
what is emerging zoonosis?
recently appeared or in a population or is recognised as ‘novel’ with rapid spread (e.g. historically HIV, henipavirus, new influenza strains, COVID)
(Morand et al., 2014)
1. what is domestication positively linked with?
2. The assembly of a shared community of pathogens…?
- time since domestication is positively linked with the number of pathogens shared with humans
- The assembly of a shared community of pathogens takes time and host range may change over following new host-parasite adaptations
Roundworms:
Are Ascaris lumbricoides and A. suum a single species?
1. how many people infected worldwide (CDC 2020)?
2. transmission method?
3. described in what year in humans and pigs?
4. what was it likely derived from?
5. what suggests they are the same species (Leles et al., 2012)?
- 807M-1.2B people infected worldwide (CDC 2020)
- fecal-oral transmission route
- described in 1758 in humans (Linnaeus), and 1782 in pigs (Goeze)
- derived from common ancestor after domestication of pigs?
- low morphological and low genetic divergence suggest they are the same species
what was the first major evolutionary change in the human diet, and why is this important?
the first major evolutionary change in the human diet was the incorporation of meat and marrow from large animals, (~ 2.6 million years ago)
… important as parasitism often interacts with predation as an effective pathway to maintain parasite transmission cycles
How did migrations and cultural changes expose humans to novel pathogens?
- colonised new environments
- changed life style and food menu
- settled and increased in population density
- had closer contact with domestic and commensal animals
- contact to novel wildlife species
Historical changes in infectious diseases burden
(Barrett et al., 1998)
1. Paleolithic age baseline
2. Neolithic revolution
3. Industrial revolution
4. Recent globalisation
- small groups of nomadic human foragers do not support many infectious agents (stone age, 3.3 mio yrs ago)
- permanent settlements, accumulation of human waste, animal domestication, and agricultural practices (12,000 yrs ago) - all close together, more opportunities for disease spread
- vaccines, control of infectious diseases and the emergence of chronic, non-infectious challenges (270 yrs ago, ~1760)
- newly emerging diseases, antimicrobial resistance (60 yrs ago, ~1970)
-> two or three major paleo-epidemiological transitions?
(Kaakoush et al., 2015)
Food-borne Campylobacter
1. what is Campylobacter jejuni?
2. is incidence/ prevalence increasing or decreasing?
3. what contributes to large-scale spread and persistence?
- one of the most widespread pathogens of the last century to cause food-borne disease
- incidence/ prevalence (campylobacteriosis) increase worldwide
- -> widespread (environmental and animal) reservoirs and self-limiting illness contribute to large-scale spread and persistence
(Oates et al., 2012; Roche et al., 2009)
Water-borne infectious diseases
1. examples?
2. transmission?
3. virulent (extremely severe or harmful in its effects) or not?
4. how protozoan parasites adopted to host tissue and environment?
5. what may protozoan parasites differ in?
- includes protozoan Cryptospordium, Giardia (and also Avian Influenza viruses)
- transmission requires contact of multiple host individuals to same water source
- often highly virulent (in the pathogen’s favour of efficient transmission: may require sufficient parasite shedding for contaminating water bodies)
- Protozoan parasites adopted to host tissue and environment through different (sexual + asexual) developmental stages
- Protozoan parasites may differ in host specificity and zoonotic risk
(Attias et al., 2020; Friesema et al., 2023)
Toxoplasma gondii:
1. what is it?
2. what does it require?
3. how are Felids infected?
4. how are intermediate hosts mostly infected?
5. what is Toxoplasmosis in intermediate hosts associated with?
- Protozoan parasite
- requires members of the cat family (felids) as definitive host
- Felids infected by consuming parasitised prey (intermediate hosts)
- intermediate hosts mostly infected by ingesting oocysts shed in the feces of the definitive host
- Toxoplasmosis in intermediate hosts associated with pregnancy failures and behavioural abnormalities -> predispose the host to predation by felids
(Torgerson et al., 2010)
Echinococcus multilocularis:
1. what is it?
2. requires?
3. what are the intermediate hosts?
4. how do definitive hosts become exposed?
5. how do intermediate hosts become infected?
6. can humans be hosts or not?
7. where is it absent from and why?
- Fox tapeworm
- requires canids (foxes, also dogs) as definitive hosts
- Arvicoline rodents (voles) as intermediate hosts
- definitive hosts become exposed by consuming parasitised intermediate host
- intermediate hosts become infected when ingesting parasite eggs
- Humans can be accidental hosts
- absent from Australia, where only dog tapeworm exists - because there are no voles
Taenia tapeworms - emerge as a product of agriculture or rather a legacy of our distant ancestors’ taste for meat?
1. transmission cycle via… ?
2. Who are the exclusive hosts for which specific Taenia tapeworms?
- transmission cycle via herbivore ungulates as intermediate host
- Humans are the exclusive definitive hosts for both the beef tapeworm (Taenia saginata), and the pork tapeworm (T. solium)
- Phylogenetic divergence: Taenia… ?
- how many times colonised and who prior to origin of modern humans?
- what was the drivers of host switching and what was the switching?
- Phylogenetic divergence: Taenia in humans pre-dates agriculture and cattle/swine domestication
- Colonised hominids twice prior to the origin of modern humans
- Dietary and behavioural shifts while entering the carnivore guild were drivers of host switching from carnivores (hyaenids and felids) in the Pliocene/Pleistocene
Ebola
1. what virus or the what?
2. recorded since?
3. how many strains out of how many strains are pathogenic to humans?
4. zoonotic: what was suggested as reservoir host?
5. what did human outbreaks coincide with?
6. data availability?
- RNA virus of the Filoviridae
- recorded since 1976 in Central Africa
- 4/5 strains pathogenic to humans
- Zoonotic: old world fruits bats suggested as reservoir host
- Human outbreaks often coincided with outbreaks in local gorilla and chimpanzee populations … BUT, these species are unlikely reservoirs as high mortality rates rule out an indefinite infection chain
- limited data availability
(Leroy et al., 2005)
Ebola
1. how many small vertebrates surveyed and where?
2. Evidence of asymptomatic infection by Ebola virus in 3 fruit bat species?
3. bat species eaten by people in central Africa show what?
- > 1,000 small vertebrates surveyed during Ebola outbreaks in humans and great apes (2001-2003) in Gabon and the Republic of the Congo
- (a) immunoglobulin G (IgG) specific for Ebola virus was detected in 16/192 (8%) sampled bat individuals; (b) viral RNA in 13/279 (5%) sampled individuals
- bat species eaten by people in central Africa show evidence of symptomless Ebola infection
(Dudas et al., 2017)
Ebola - Why do Ebola epidemics not spread further?
1. How many publicly available EBOV genomes and from where?
2. what was constructed?
3. what was inferred?
4. EBOV spread suitability?
- 1,610 publicly available EBOV genomes (2014-2015 epidemic) from Liberia, Sierra Leone, Guinea
- construct phylogenetic tree
- infer the spatial phylogenetic diffusion history
- EBOV did not spread into all suitable areas, locally contained epidemics
Ebola
1. what does the metapopulation model reveal?
the persistence of the epidemic to be driven by introduction into novel contact networks rather than by mass-action transmission (such as susceptible-infectious-removed dynamics)
(Gage & Kosoy, 2005; Levi et al., 2016)
Plague: from enzootic to epizootic cycling
1. Yersinia pestis is primarily a disease of what?
2. enzootic cycle?
3. epizootic cycle?
- rodents and their fleas
- enzootic cycle: transmission between partially resistant hosts
- epizootic cycle: transmission to more susceptible and amplifying species
(Carrat & Flahault, 2007)
1. antigenic drift?
2. antigenic shift?
- antigenic drift - small changes/mutations in genes that can lead to changes in the surface “antigen” proteins of the virus (hemagglutinin and neuraminidase)
-> main reason why people can get the flu more than one time
-> also a primary reason why the flu vaccine composition must be reviewed and updated to keep up with evolving influenza viruses - antigenic shift - abrupt, major changes in the surface “antigen” proteins of the virus (hemagglutinin and neuraminidase), resulting in new virus subtypes. One way shift can happen is when an influenza virus from an animal population gains the ability to infect humans. Low immunity in host population can cause pandemics (‘immune escape’)
(Wolfe et al., 2007)
5 evolutionary stages in the evolutionary transformation of an animal pathogen into a specialised human pathogen
- with examples for each stage
- Pathogen confined to animals - some Plasmodium strains (e.g. rodent or avian malaria)
- Infects human without secondary infections - Nipah, rabies, and West Nile viruses
- Pathogen able to sustain a few cycles before the outbreak dies out - Ebola, Marburg and moneypox viruses
- Pathogen able to sustain many cycles of human-to-human transmission - Chagas’ disease, influenza A, (sylvatic and direct transmission of different importance)
- Pathogen exclusively infecting humans - P. falciparum malaria, measles, mumps, rubella
Lecture 2 Slide 26 - disease, agent, transmission, vector, animal reservoir, and likely origin
Lecture 2 Slide 26 - disease, agent, transmission, vector, animal reservoir, and likely origin
(Wolfe et al., 2007)
Origin of infectious diseases - temperate/ tropical differences in disease characteristics?
- high proportion of diseases is transmitted by insect vectors in the tropics (8/10 vs. 2/15)
- a higher proportion of the diseases conveys long-lasting immunity in temperate zones
- animal reservoirs are more frequent in the tropics
- most of the temperate diseases are acute rather than slow, chronic, or latent
- most temperate diseases are ‘crowd epidemic diseases’ (persisting regionally only in large human populations)
Pathogen Diversity
How many pathogens known to be infectious and capable of causing disease in humans under natural conditions?
1. first comprehensive list by Taylor et al. (2001)?
2. list by Wardeh et al. 2015?
- 1,415 species (217 viruses and prions, 538 bacteria and rickettsia, 307 fungi, 66 protozoa and 287 helminths)
- 2,107 species (274 viruses, 1003 bacteria, 447 fungi, 82 protozoa and 301 helminths)
(Carroll et al., 2018)
Global Virome project
111 virus families discovered until 2018
of these - 25 families containing viruses known to infect people (or substantial risk)
in these 25 families, 1.67 million unknown viruses in mammals and birds
of these, 631-827,000 likely to have capacity to infect people
Pathogen diversity - how many species
1. estimates based on… ?
2. estimates of how many viruses have the potential for what?
3. total estimates of viruses in mammals?
- estimates based on network properties (pattern of new host-pathogen association to share multiple know host species)
- estimates of ca. 10,000 viruses with zoonotic potential that are emerging at a slow but accelerating pace
- total estimate of ~ 40,000 viruses in mammals (opposed to 1.67 million by Carroll et al. 2018)
Pathogeography
what are relevant to understand biogeographical patterns and the distribution of pathogens (and other organisms) on Earth?
species- and community-level approach
Measuring beta diversity - Lecture 2 slide 34
Measuring beta diversity - Lecture 2 slide 34
Pathogeography (community-level)
(Murray et al., 2015)
Infectious disease assemblages remain fundamentally constrained in their …
… distributions by ecological barriers to dispersal or establishment, despite the homogenizing forces of globalisation
Pathogeography (community-level)
(Murray et al., 2015)
what is pathogen spread limited by?
pathogen spread can be limited in space and time, community-level turnover differs among groups
pathogens transmitted between humans least constraint in their spread?
