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DISEASE E&E Final Exam > 16. Multi-Host Pathogens and Host Extinction > Flashcards

16. Multi-Host Pathogens and Host Extinction Flashcards

1
Q

Multi-host pathogen:

A

-pathogen that infects multiple host species
-can have reservoir and dead-end hosts
>can exist in dead-end hosts due to repeated introduction from the reservoir host

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2
Q

Reservoir hosts:

A

-pathogen has sustained transmission
-R0>1

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3
Q

Dead-end hosts:

A

-incompetent
-pathogen dies out
-R0<1

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4
Q

Pathogen with only one reservoir host:

A

-single-host pathogen

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5
Q

Pathogen with one reservoir host and many dead-end hosts:

A

-multi-host pathogen

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6
Q

Pathogen with multiple reservoir hosts:

A

-multi-host pathogen

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7
Q

Pathogen that has multiple dead-end hosts: (with no reservoir host)

A

-cannot exist

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8
Q

Host range:

A

-number of hosts that a pathogen can use to maintain itself in nature
Ex. do NOT count dead-end hosts

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9
Q

Generalist pathogen:

A

-has a large host range
>can persist indefinitely and independently in multiple hosts
-R0>1, for at least 2 host species
*all are multi-host pathogens

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10
Q

Specialist pathogen:

A

-has a small host range
>can only persist in 1 host

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11
Q

Multi-host pathogens:

A

-not all are generalists
-can establish infection in multiple host species, but not necessarily be maintained independently in them

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12
Q

Example of generalist pathogen:

A

-can independently persist in host species A and B
>if host species A goes extinct, pathogen will PERSIT in host species B and vice versa

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13
Q

Example of multi-host pathogen:

A

-can infect host species A and B
-host species A is a reservoir host
-host species B is a dead-end host
*if species A goes extinct, the pathogen will go extinct

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14
Q

Example of single host pathogens: specialist pathogens in humans

A

-HIV
-measles virus
-smallpox virus
-treponema pallidum

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15
Q

Special pathogens in humans:

A

-no suitable animal models have been found to study these pathogens
>*specialist or single-host pathogens
-R0>1 only in human populations

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16
Q

Rinderpest virus: multi-host pathogen

A

-infectious viral disease of even-toed ungulates
-cattle and buffalo have mortality rates of 100%
-sheep and goats have less serious disease
-pigs and deer have asymptomatic disease

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17
Q

Host range of rinderpest virus:

A

-cattle
-sheep
-goats
-pigs
-domestic and wild buffalo
-large antelope
-deer
-giraffes
-wildebeests
-warthogs

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18
Q

Bd (Batrachochytrium dendrobatidis): multi-host pathogen

A

-fungal pathogen that infects hundreds of amphibian species
-contributed to decline of 501 amphibian species (chytridiomycosis)
*greatest documented loss of biodiversity attributable to a pathogen

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19
Q

Bd: one of the most destructive invasive species

A

-comparable to rodents and cats
>threatening over 420 species

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20
Q

Host specificity:

A

-compared morphology and genetics

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21
Q

Morphological studies:

A

-found that a single ‘generalist’ pathogen species was found in different host species

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22
Q

Genetics reveals:

A

-that ‘generalist’ pathogen is a complex of ‘specialist’ pathogens
-each species/strain/variant is specific to one or only a few host species

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23
Q

Pathogen/parasite species:

A

-often cannot be identified using morphology
*molecular biology has revolutionized detection of diversity of pathogen species/strains/variants

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24
Q

Rabies virus is complex of variants:

A

-in NA: classic multi-host pathogen
-infects different species of mammal in NA
-genetics found genetic variations associated with different host species

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25
Q

Rabies virus variants:

A

-mostly circulate in a single reservoir species
-are specialized to complete life cycle in preferred host
*associated with major mesocarnivore species are distributed in distinct geographic regions

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26
Q

Rabies virus variants examples:

A

-bat rabies
-skunk rabies
-racoon rabies
-fox rabies
-monogoose rabies

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27
Q

Cross-species transmission of rabies:

A

-does occur (ex. dogs with raccoon rabies variant)

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28
Q

Majority of human pathogens are zoonotic:

A

-1415 species of infectious organisms that cause disease in people
>61% zoonotic (1 human host, 1 non-human host =2 hosts)
*many pathogens can infect multiple host species

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29
Q

Zoonotic pathogens:

A

-are multi-host pathogens (can infect more than 2 host species)
>not necessarily generalist pathogens
*many can spillover into humans, but CANNOT maintain themselves in human populations (ex. WNV)

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30
Q

What do theoretical models say?

A

-Roy Anderson and Robert May developed the science of epidemiology
-created models for many infectious diseases in humans

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31
Q

Simplest disease models:

A

-suggest that disease alone CANNOT drive host populations extinct (ex. rabies in foxes)
>these consider a single host and a single pathogen
>multi-host pathogens are considered

32
Q

De Castro and Bolker (2005):

A

-when there is density-dependent transmission, the pathogen will always go extinct before the host species (ex. rabies in red foxes)
-if pathogen reduces the host population, R effective will eventually be <1
>the pathogen will disappear from host population

33
Q

IUCN red list categories:

A

-red list of threatened and endangered species
-contain all species that are extinct or critically endangered
-indicates threats that have caused species declines or extinctions
-use red list to determine role of infectious disease in global species loss

34
Q

Major threats to species:

A

-habitat destruction
-overexploitation
-invasive species
-infectious diseases (ID)

35
Q

Infectious disease and host extinction:

A

-responsible for some extinctions and critically endangered status
-contribute to <4% of species extinction
-contribute to <8% of critically endangered status
>75% of them are amphibians

36
Q

75% of amphibians are critically endangered from ID:

A

-because of fungal pathogen, Bd

37
Q

ID and extinction conclusions:

A

-play a minor role in global species loss and never act alone to cause extinction
*most import causes of extinction and threaten status are HABITAT LOSS and OVEREXPLOITATION

38
Q

Mechanisms of disease-induced extinction: small populations

A

-Allee effects
-inbreeding effects

39
Q

Mechanisms of disease-induced extinction: non-density dependent transmission

A

-frequent-dependent transmission
-sexually transmitted diseases

40
Q

Mechanisms of disease-induced extinction: reservoirs

A

-biotic: apparent competitors (multi-host pathogens)
-abiotic: amplification in the environment

41
Q

Allee effects:

A

-occur when the per capita growth rate declines at lower densities
-occur in social organisms with cooperative behaviour
Ex. 12 wolves better at catching prey than 2 wolves

42
Q

Allee effects: Passenger pigeon

A

-endemic to NA
-population of 3 billion birds
*hunting and habitat loss ->extinction
>decreased below the threshold necessary to propagate the species

43
Q

Decrease in passenger pigeon:

A

-it made it harder for few or solitary birds to locate suitable feeding areas

44
Q

Passenger pigeon summary:

A

-flocks of a few thousand or hundred thousand birds, may not be enough to sustain the species
>innate behaviour which made them search for mother flock of millions of individuals which no longer existed

45
Q

Small populations: breeding

A

-have reduced genetic variation compared to large populations
*have inbreeding
>expression of deleterious recessive alleles

46
Q

Inbreeding depression:

A

-decrease in fitness in population
-vulnerable to novel pathogens

47
Q

Cheetahs and inbreeding:

A

-highly inbred
-highly susceptible to feline coronavirus (FCoV)
-wouldn’t need immune supressing drugs for an organ transplant

48
Q

Density-dependent transmission:

A

-per capita contact rate between S and I depends on host population density
>transmission rates increase with density of I and uninfected individuals

49
Q

Frequency-dependant transmission:

A

-per capita contract rate between S and I individuals does NOT depend on the population density
>transmission depends on prevalence of infection

50
Q

STDs:

A

-modelled with frequency-dependent transmission
Ex. chlamydia in koalas

51
Q

Chlamydia in koalas: causes

A

-blindness
-bladder inflammation
-infertility
-death

52
Q

Chlamydia in koalas: treatment problem

A

-antibiotics
>kills gut microbes and blocks digestion of eucalyptus leaves

53
Q

Grey squirrels vs. red squirrels in UK:

A

-less red squirrels (140,000) compared to grey squirrels (2.5million)
-red: native, around for 10,000 years
-grey: introduced in 1800s and escaped and established a wild population (1876)

54
Q

Change in distribution of red squirrel:

A

-1945 to 2010: grey squirrels expanded their range at expense of red squirrels

55
Q

Grey squirrels:

A

-weigh more
-consume more energy
-use 1.65x more food energy
*replacement of reds by greys driven by superior competitive ability of greys
>competition is explanation for replacement

56
Q

Competition hypothesis: grey and red squirrels:

A

-suggests that inter-specific competition between 2 squirrel species explains replacement

57
Q

Squirrelpox virus:

A

-causes squirrelpox in red squirrels
-introduced to UK with the introduction of grey squirrels

58
Q

Squirrelpox in red squirrels:

A

-mortality rate is 100%
>no immunity
-most die within 5 days

59
Q

Squirrelpox in grey squirrels:

A

-mild
>rarely die from disease
*have evolved immunity to virus
-asymptomatic carries that spread disease to reds

60
Q

Experimental infections:

A

-2002
-discovered asymmetric effects of squirrelpox on red and grey squirrels
*model: speed of replacement not consistent with competition alone

61
Q

Competition vs. squirrelpox:

A

-competition over food resources is considered the PRIMARY cause of the decline of red squirrels
>no detectable effect on grey squirrel health
-minor role of squirrel pox because diseased red squirrels rarely seen outside highly localized epidemics

62
Q

2 models of replacement of reds by greys:

A
  1. Competition: replacement takes 15 years
  2. Competition and infection: replacement takes 6 years = matches observations in nature
    *predicts speed of replacement at local scale and not for all of UK
63
Q

Infected squirrels are rare: competition and infection

A

-need different scales because of the abundance of I is much much lower than abundance of S or R

64
Q

Abundance of infected reds and greys:

A

-low

65
Q

Abundance of recovered greys:

A

-very high
*can use antibody tests to measure prevalence of grey squirrels that have antibodies against squirrelpox

66
Q

Summary of smallpox example:

A

-tradition (incorrect) explanation: competition alone is driving replacement; squirrelpox is not important
-speed of replacement is best explained by competition and squirrelpox
-prevalence of infected individuals are low in both reds and greys
-virulent with low prevalence can have a big impact
*ecologists underestimate importance of ID

67
Q

Interspecific competition occurs:

A

-if invasive and native species occupy same ecological niche

68
Q

Invasive species use pathogens as bioweapons:

A

-pathogens can influence success of many invasive species
>brings pathogen to its new habitat and causes disease in native species
*pathogen gives invasive species a competitive advantage over the native species

69
Q

Christmas island rat:

A

-was endemic to Christmas island
-135km^2
-within 10 years of first contact with European sailors, they had gone extinct
-determined cause of extinction 100 years later (2008)

70
Q

Christmas island rat, black rat, and trypanosome:

A

-trypanosome caused the extinction
>introduced by black rats that jumped ship from European boats
-2008, found DNA from the trypanosome parasites in the museum specimens of the CI rats
>only found in rats after first contact
*first example of mammal driven to extinction by parasite

71
Q

Ethiopian wolf:

A

-one of the rarest canids
-listed as endangered by IUCN
-limited to 7 isolated mountain ranges at altitudes of 3000-4,500m

72
Q

Threats of the Ethiopian wolf:

A

-expanding human populations
-habitat degradation
-disease from free-ranging dogs

73
Q

Multi-host pathogens can influence:

A

-competition between host species and drive vulnerable host species to extinction
>invasive species introduce pathogens to native species that are often threatened due to other reasons
-may be asymptomatic in invasive species and causes serious disease in vulnerable native species
>act as reservoirs
>drives native species to extinction

74
Q

Asymmetric effects of multi-host pathogens:

A

-squirrelpox in red and grey squirrels
-trypanosome parasites in Christmas island rats and European black rates

75
Q

Multi-host pathogen is equally deadly:

A

-to both native host and invasive host
Ex. rabies in Ethiopian wolf and domestic dogs

DISEASE E&E Final Exam (11 decks)

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