steve Flashcards
1
Q
What percent of human pathogens are generalists that infect multiple hosts?
A
60%
2
Q
What percent of carnivore pathogens are generalists that infect multiple hosts?
A
90%
3
Q
In terms of only human pathogens, what is more likely to be a generalist, ermerging diseases or old diseases?
A
Old diseases
4
Q
2 hotspots of pathogen richness
A
South America and Africa
5
Q
What kind of transmission is single host-pathogen system?
A
Density dependent transmission
6
Q
What type of transmission is beta11 and beta22
A
Intraspecific
7
Q
What type of transmission is beta12 and beta21
A
Interspecific
8
Q
2 scenarios of cross species transmission
A
At least one interspecific transmission non existing, mutual interspecific infection
9
Q
The first scenario of cross species transmission says that what?
A
Pathogen can only persist if it can persist on one host alone
10
Q
What is the spillover effect?
A
One host is capable alone of supporting the pathogen - i.e. it “spills over” into the second host resulting in some level of infection in that host
11
Q
2 different ways scenario 2 of cross species transmission
A
Interspecific transmission < intraspecific transmissions, interspecific transmission > intraspecific transmission
12
Q
If interspecific transmsiiions < intraspecific transmission, what allows the pahtogen to persist?
A
Two host densities combine
13
Q
What scenario of mutual interspecific transmission allows the pathogen to exist in the least abundance?
A
Interspecific > intraspecific
14
Q
Example of pathogen spill-over study
A
A. fatua that is a good host for barley yellow dwarf virus
15
Q
What did the A. fatua study find?
A
Pathogen spill-over strongly increased pathogen prevalence in the other plants in the community
16
Q
Within density-dependent transmission, what does pill-over dynamics do to host population density and fitness?
A
Decreases it
17
Q
Within density-dependent transmission, what kind of interactions between host populations are mediated by the pathogen?
A
Negative (indirect)
18
Q
Within density-dependent transmission, what does an increase in one host due to pathogen prevalence in the other host? Host density?
A
Increases, decreases
19
Q
What does the theory of amplification effect say?
A
Multiple hosts could facilitate pathogen persistence and amplify pathogen abundance
20
Q
What is the main study showing support for the amplification effect?
A
Lyme disease vs bird host diversity
21
Q
What kind of pathogens are most interspecific pathogens?
A
Vector transmitted
22
Q
Cross-species transmission is usually what kind of transmission?
A
Frequency-dependent
23
Q
Within frequency-dependent transmission, what effect does a second host have on a pathogen?
A
Makes its persistence less likely
24
Q
What is the dilution effect and what type of transmission does it deal with?
A
Host numbers dilute per capita transmission rate of frequency-dependent transmission
25
Example of dilution effect
West Nile virus
26
More or less disease: Additive species and frequency-dependent transmission
Less
27
More or less disease: Substitutive species and frequency-dependent transmission
Less
28
More or less disease: Additive species and density-dependent transmission
More
29
More or less disease: Substitutive species and density-dependent transmission
Less
30
True or false: Multi-host systems can either increase or decrease the probability of persistence of a pathogen dependent on transmission mode
True
31
True or false: Most cross species infection follows density-dependent transmission type
False
32
True or false: Increased biodiversity usually increases disease prevalence and risk of infections
False
33
True or false: Frequency-dependent transmission pathogens can drive a single host to extinction
True
34
3 general patterns of dilution effect
Sharing a pathogen can rescue a host from extinction, most likely if second host is a "bad" host for the disease, extinction unlikely since it requires high interspecific transmission rates than intraspecific rates
35
2 ways that sharing a pathogen can rescue a host form extinction
Frequency-dependent dilution effect, dilution effect exceeds interspecific infection
36
Animal(s) where increased species richness increase lyme disease prevalence; animal(s) where increased species richness decreases lyme disease prevalence
Birds; mammals and lizards
37
3 conditions where positive effects of hosts sharing pathogens are likely to be seen
Alternative host reduces intraspecific transmission rate in other host, alternative host is more resistance to disease, interspecific transmission rates are lower than intraspecific transmission rates
38
What pathogen causes lyme disease?
Borrelia burgdorferi
39
What is lyme disease transmitted by?
Black legged tick
40
Addition of non-human host to "siphon" vector meals away from humans
Zooprophylaxis
41
When a host is asymptomatic and not infectious
Latent
42
When a host is asymptomatic and infectious
Carrier
43
Time from infection to symptoms
Incubation period
44
Time from infection to transmission
Latent period
45
2 meanings of the word "virulence"
Measure of disease severity once host is infected, measure of the pathogen's ability to infect the host
46
3 by-products of pathogen adaptation
Direct use of host resources for growth and reproduction, damage during growth and multiplication, damage during transmission
47
2 by-products that are incidental to pathogen adaptation
Long-term damage well after transmission, suppression of host defenses against other pathogens
48
True or false: use of host nutrients for growth and reproduction is frequently not a major reason for pathogenesis
True
49
3 exceptions to the theory that using host nutrients for growth and reproduction is not a reason for pathogenesis
Bacteriophages, parasitioids, macro-parasites
50
3 examples of damage during growth and reproduction within host that damages humans
Malaria, flesh-eating bacteria, gangrene
51
Plant pathogen that needs living tissue to reproduce
Biotrophic
52
Plant pathogen that kills tissue and feeds on dead remains
Saprotrophic
53
4 examples of damage during transmission of pathogen
Sleeping sickness, syphilis, cholera, brucella ovis
54
What is brucella ovis?
STD that causes abortions in cows; returns cows to oestrus and mating
55
2 examples of damage occurring well after infectious period that is non-adaptive for a pathogen
Tertiary syphillis, atheroscelerosis
56
What is tertiary syphilis?
Formation of soft tumor like balls of inflammation in tissue
57
What is atheroscelerosis?
hardening of arteries caused by pneumonia
58
Example of inactivation of host defenses against other pathogens
AIDS
59
3 ways fever combats disease
activates immune system, lowers iron concentration in blood, slows bacterial growth
60
6 ecological or behavioral resistances
active repulsion, cleaning, avoidance of infected sites, avoidance of infected individuals, social structure, self medication
61
Example of herding and parasite avoidance
Behavior of horses to avoid horseflies
62
Physiological/biochemical resistance that is there all the time
Constitutive
63
Physiological/biochemical resistance that is induced by the presence of the pathogen
Inducible
64
2 advantages of constitutive defense
Pre-emptive, no time delay
65
3 disadvantages of constitutive defense
Operate in absence of pathogen, difficulty in specificity, mechanisms may act as cues for specialized pathogens
66
Example of constitutive defense in humans
Ciliated cells in upper respiratory system
67
4 advantages of inducible defense
Only expressed when needed, valuable for "costly" defenses, can be "tailored", some only effective when inducible
68
3 disadvantages of inducible defense
requires prior exposure, costs of constructing system, self-damage costs
69
Main problem with inducible defense
Distinguishing pathogen from self
70
3 examples of harmless nonself
Food, harmless organisms in environment, genetically different individuals of same species (e.g. sperm, offspring)
71
3 mechanisms of non-self recognition
Be a systematist, label self, generate cells that attack everything but remove those that recognize self
72
Reject other individuals based on differing taxon characteristics
Systematist
73
Reject unlabelled individuals
Label Self
74
Example of cells that attack everything, but remove those that recognize self
Vertebrate immune system
75
2 ways hosts distinguish bacteria from self
Cell wall constituents, flagellin
76
2 ways hosts distinguish fungi from self
cell wall and membrane constituents
77
Example of a host labeling self and rejecting unlabeled
Methylate DNA, degrade un-methylated DNA
78
Example of an "island effect" - too low genetic diversity resulting in outbreak of disease
Tasmanian devils with low diversity of MHCs
79
4 factors that constrain directional selection on host resistance
Lack of genetic variation in host, cost of resistance, heterozygote advantage, frequency dependent selection
80
How might a resistant host have lower fitness than a susceptible host?
Poorer competitor, lower fecundity, slower growth, delayed maturity
81
What can small resistance costs lead to?
Maintenance of genetic polymorphism
82
Instances where it is better to have two different alleles than a homozygous genotype
Heterozygote advantage
83
Why is heterozygote advantage actually advantageous?
Ideally, you can defend against 2x as many pathogens
84
Example of heterozygote advantage in animals
Harbor seals resistant to lung-worm
85
Example of heterozygote advantage in humans
Sickle cell anemia
86
What does the diversity of MHC receptors determine?
How many antigens the immune system can recognize
87
3 reasons why do MHC genes undergo rapid evolution?
Pathogens continually evolving, new pathogens have non-recognizable antigens, might allow host response to unpredictable and frequent disease outbreaks
88
What type of MHC diversity has the highest fitness?
Intermediate
89
What happens when MHC diversity is too low?
Not good enough to deal with novel pathogens
90
What happens when MHC diversity is too high?
Autoimmune responses
91
What is frequency dependent selection
Fitness of different genotypes depends on their relative frequencies
92
How does frequency dependent selection operate?
Pathogens adapt to infect most "common" genotype, and make it rare, leading to cyclical dynamics
93
2 predictions of red queen hypothesis
Changes in host genotype frequency should lead to time-lagged changes in infection frequency, parasites should be most infective in common hosts genotypes
94
What does pathogens selecting for increasing host defenses and hosts selecting for new pathogen variants result in
Evolutionary "arms race"
95
Ways that pathogens are able to win evolutionary arms race
faster generations, larger populations, higher mutation rates, lateral gene transfer
96
Way that hosts are able to win evolutionary arms race
Larger genome
97
What did the Lenski experiment try to solve?
The evolutionary arms race using lab cultures to investigate bacteria vs phage
98
Change in gene frequencies over time
Evolution
99
Gradual non-random process by which heritable traits that increase organism's fitness in a given environment are more favored than less beneficial traits
Natural Selection
100
2 assumptions made when using pathogens as evolutionary agents
Pathogens exert selective pressure on hosts by causing differential survival or reproduction, selection leads to changes in gene frequencies in the host
101
3 things that parasite-mediated selection requires
Parasite numbers vary among individuals in population, variation parasite number must be associated with variation in fitness, trait to be mediated must co-vary with parasite number
102
Which of the 3 ways of parasite-mediated selection is not common
Trait to be mediated must co-vary with parasite number
103
2 things that parasite-mediated evolution requires
Parasite mediated selection, heritability of trait of interest
104
What happens when variation is not heritable?
Selection without evolution
105
The potential for evolution under particular conditions
Heritability
106
How does one measure heritability
h^2, but difficult
107
A mutation in what receptor causing the HIV resistance?
CCR5
108
Where were mutations in the CCR5 gene first seen?
Central Europe
109
A mutation in what gene causes sickle cells
Hemoglobin gene
110
2 long term advantages of sexual reproduction
Populations without sex go extinct, recombination acts as a repair mechanism for deleterious mutations
111
2 short term advantages of asexual reproduction
Adaptation to variable abiotic environments, adaptation to ever changing pathogen pressures
112
Which has a reduced BYDV infection rate: sexually produced progeny or asexually produced?
Sexually produced
113
What is the abundance of trematode prevalence among snails determined by?
Abundance of birds
114
How does mate choice affect disease spread?
Direct assessment of disease status
115
2 exaggerated secondary sexual characters that are used as indicators of disease status
Bright plumage, active courtship displays
116
2 assumptions for parasite-mediated sexual selection
Health status is reflected in secondary sexual characteristics, females choose males with such characteristics to obtain "good genes"
117
Do swallows get a lot of diseases?
YES!!!
118
Highest prevalence among swallows
Ornithonyssus (mite)
119
How does disease among swallows manifest itself in sexual selection?
Tail feathers grow less on diseased swallows, with tail length direct indicator of disease level
120
What does the fact that offspring of males with longer tails having fewer mites independent of where the offspring were raised suggest
More genetically resistant
121
True or false: sexual reproduction is intrinsically costly
True
122
True or false: Progeny produced by asexual reproduction have a direct ecological advantage over sexual progeny
False
123
True or false: Sexual selection provides faster mechanism for evolution of host resistance
True
124
3 ways that conventional wisdom, "Parasites evolve to become benign" fail
sleeping sickness, river blindness, insect mushrooms
125
What happens to someone infected with sleeping sickness
Alters circadian rhythm, leads to coma and death
126
What happens to someone infected with river blindness
Permanent blindness
127
What happens to an insect that is infected with insect mushrooms
Fungi cause hosts to fly or crawl to high spots and then die so spores can go further
128
True or false: Parasites that rely on host mobility or behavior should be less virulent than those that are vector-transmitted
True
129
If virulence is costly, why be virulent at all?
Virulence often co-varies with other factors that carry direct beneits
130
Example of virulence direct benefits
Increased numbers within a host increase the likelihood of spreading to a new host
131
What ultimately determines optimal virulence of a pathogen?
Fitness curve between virulence and parasite fitness
132
True or false: shape of fitness curve (virulence vs parasite fitness) is unknown for almost all pathogens
True
133
What is myxoma?
DNA virus that infects rabbits and causes tumors
134
2 ways that virulence is altered
Hosts evolve, spatial structures
135
How does spatial structure alter virulence?
Spatial clumping decreases virulence
136
What does spatial clumping decrease virulence?
CHanges in transmission virulence trade-off
137
What does old Paul Ewald have to say about virulence?
Transmission strategies determine optimal level of virulence, parasites that rely on host mobility should be less virulent than those that are vector-transmitted
138
How does the tragedy of the commons apply to virulence?
If another pathogen has invaded your host, you should use up the host resources as fast as possible so your competitor doesn't get them
139
What prediction can be made in terms of tragedy of the commons applied to virulence?
Pathogens in mixed infections should have higher virulence than those in single-clone infections
140
True or false: Pathogens always try to maximize their transmission rates
True
141
True or false: Evolution of virulence driven by trade-off between costs and benefits
True
142
True or false: Optimal virulence is usually at the maximum
False
143
What can the virulence-transmission trade-off be altered by?
Environmental factors and transmission modes
144
Evolutionary history of a group
Phylogeny
145
How is phylogeny represented?
Tree
146
Part of phylogenetic tree that is a point divergence between taxa
Node
147
Part of phylogenetic tree that describes the relationships between taxa
Branch
148
Part of phylogenetic tree that describes most recent common ancestor of all taxa
Root
149
3 things that support for a phylogenetic tree comes from
Additional genes, additional taxa, evidence from geology
150
3 uses of phylogenies in disease biology
pathogen relationships and control, understanding emerging diseases, tracing disease epidemiology
151
3 things that understanding evolutionary relationships helps with
What control mechanisms are effective, culture techniques, features determining virulence
152
What does molecular epidemiology seek to do
Trace spread of disease through populations using comparative gene sequence data
153
What do successful strains of a pathogen have in common?
High rate of substitutions at particular codons
154
Parasitism by an organism on or in another parasite
Hyperparasitism
155
What is at the top of an Elton's pyramid of predation
Secondary predator
156
What is at the top of an Elton's pyramid of parasitism
Hyperparasite
157
2 examples of decreased virulence as a result of a hyperparasite
Virophage, dsRNA virus,
158
3 examples of virophage
A. polyphaga, mamavirus, sputnik
159
What are dsRNA viruses?
Viral-like genomes, often naked RNA molecules
160
Example of dsRNA virus
Chestnut blight
161
What does chestnut blight do?
Destroy bar, causing death of tree
162
Example of increased virulence as result of hyperparasite
Bacteriophage
163
Parasitism of members of the same species
Homoparasitism
164
Where do most examples of homoparasitism occur?
Ticks
165
What do homoparasitic ticks do?
Feed on hemolymph
166
One way that hyperparasitism benefits humans?
Biological control agents to control insect pests
167
How was mealybug invasions reduced?
Parasitoid wasps were released
168
What is the fungus Ampelomyces used to control?
powdery mildew
169
True or false: hyperparasitism is common
True
170
True or false: hyperparasitism cannot alter virulence of their host
False
171
What is a host shift?
Novel host-pathogen combination that become a new disease
172
3 types of emerging infectious diseases
No transmission, transient host shift; transmission on new host, not self sustaining; transmission and self-sustaining
173
3 factors favoring evolution in pathogens
Large numbers of source hosts, many contacts with new hosts, transmission in new host
174
Why does large numbers of source hots favor evolution?
More mutations/variants
175
Why does many contacts with new hosts favor evolution?
More selective trials
176
Why does transmission in new host favor evolution?
More mutation and selection
177
2 strategies to control host shifts
Limit number of generations in humans, limit population size
178
What is serial passing experiments?
Experimental host shifts to determine how quickly pathogens adapt to new hosts
179
True or false: once a host-shift occurs, specialization to new host is slow
False
180
3 impacts of predators
Removal of sick, old, weak; reduce population of prey, result in cyclical population dynamics
181
What does removal of "sick, old, weak" result in?
Reduction of infecteds within the population
182
What does reducing population of prey result in?
Reduces contact rate for density-dependent transmission
183
What does cyclical population dynamics result in?
COntact rate may vary dramatically over time
184
True or false: specialist predators (i.e. that prey on only sick/weak) will reduce disease risk to humans
False
185
How do generalist predators impact prey cycles?
Less likely to result in them
186
2 characteristics of generalist predators
Can regulate prey populations to low levels over large areas, highly mobile
187
What happens when predators don't consume prey whole?
Spread infective stages of a pathogen
188
2 non-consumptive effects of predators?
Changes in behavior, changes in physiology
189
3 changes in behavior due to predators
clumping together, reduction in activity levels, changing habitat preferences
190
2 changes in physiology due to predators
inducible defenses, re-allocation of energy
191
2 things that are always at the top of the food chain
Parasites, pathogens
192
If there are N species, how many connections of a food chain can there be?
N^2
193
True or false: parasites are more specialized than predators or scavengers
True
194
1 factor that increases the risk of secondary extinction of hosts
Complex life cycles of parasites
195
What did Kuris and Lafferty find in a study on a California marsh?
Higher percentage of linkages of a food chain when parasites are considered
196
True or false: Pathogen/parasite biomass exceeds that of top predators
True
197
In a coastal marsh, what is the birth rate of trematodes in terms of elephants
One elephant/day
198
What is the highest modern cause of species extinction
Habitat destruction
199
What is the lowest modern cause of species extinction?
Disease
200
True or false: Disease is likely to be lost when populations get small and/or isolated from each other
True
201
2 general principles of disease-caused extinction
Host specific pathogens and parasites, generalist pathogens
202
2 deterministic events that led to a decline in black footed ferrets
Loss of habitat/food resources, fragmentation/isolation
203
3 stochastic events that led to a decline in black footed ferrets
Disease, very small population, inbreeding
204
How did several bird species of Hawaii go extinct?
Bird malaria introduced by invasive birds and malaria
205
What did Pedersen's 2007 study on the assessment of threatened species find?
Direct evidence of parasites causing population declines or substantial negative effects on fitness
206
2 types of IUCN classifications of "threatened"
By pathogens, by other factors
207
True or false: most threatened species are closely related to domestic species
True
208
What percent of threatening parasites can infect multiple hosts?
66%
209
WHat percent of threatening parasites also infect domestic animals
96%
210
Major threat to wildlife-diseases
Spill-over effects from domesticated animals
211
Theory that says many invasive and pest species are successful because they have left their natural enemies behind
Enemy-escape hypothesis
212
How does loss of diseases affect invasions?
Direct effect of population regulation, reallocation of resources from defense to reproduction
213
What is a "healthy" ecosystem
Ecosystem persists and maintains productivity, biodiversity, resilience
214
How can larval trematodes that parasitize snails be used by humans>
Measure habitat restoration success
215
About how many cannibalistic species have been identified?
>1500
216
2 things that consumption of sick conspecifics often lead to
Infection, reduction in survival and growth
217
Disease can only spread though cannibalism by?
Group cannibalism
218
True or false: disease-mediated extinction is one side effect of canibalism
False
219
True or false: disease transmission through "conspecific necrophagy" requires group cannibalism
True
220
4 things of the war on infectious diseases
development of antibiotics, controlled vaccination programs, public health measures, social measures
221
2 public health measures
public sanitation, chlorination of water supply
222
2 social measures
improving housing, reducing poverty and over-crowding
223
How many people die of infectious diseases per year
8 million
224
Main cause of death by infectious diseases
Lower respiratory tract diseases
225
Hot spots of emerging pathogens/diseases
India, Africa, southeast asia
226
3 causes of antibiotic resistance
unnecessary prescriptions, use in animals, evolution
227
First pandemic of 21st century
SARS
