Parasitology Exam 2 Study Guide

Flashcards covering core parasitology concepts, helminths, parasite ecology, host-parasite coevolution, and parasite impacts on hosts and ecosystems from the Exam 2 study guide.

What are digeneans (trematodes), and what are their primary biological characteristics?

These are endoparasites that live in the blood vessels, digestive tract, or inside vertebrate hosts and release a free-swimming stage called cercariae. They have complex, multi-host life cycles that involve a mollusk host.

Ex: flukes

Natural selection

Individuals with advantageous traits help them survive and reproduce, making them more common over generations

Abiotic and biotic factors

Abiotic Factors (nonliving): host struggles to regulate body temperature if the environment becomes too hot or too cold

Biotic Factors (living): host isn't getting enough food (starvation), or host is being eaten by a predator (has lower ability to escape them)

Trophic transmission

A parasite is transmitted from one host to another as an infected host gets eaten by another host.

Digenean trematode example:

1. A fish has a parasite in it.

2. Then a bird eats that fish.

3. Then that bird gets the parasite and is now infected with it

• Trophic transmission

  • Can you give an example of a parasite with this mode of transmission?

Digenean trematodes: A bird becomes infected when it eats a fish containing the parasite

Parasitic castration

A parasite fully prevents its host from reproducing, reducing fecundity (offspring) to zero.

Parasitic castration

• Can you give an example of a parasite with this mode of transmission?

Larval trematodes can parasitically castrate snails, preventing them from reproducing.

Virulence

The degree of harm a parasite causes to its host.

Evolutionary fitness

An organism's reproductive success or how well it passes its genes to the next generation.

Fecundity

The amount of offspring and organism can reproduce

Define what a helminth is

These are parasitic worms. They didn't all come from one parasitic ancestor, as they've evolved independently into different groups of worms.

Recognize a group as helminths

platyhelminthes which are flatworms. They are a diverse phylum containing approximately 30,000 species, with about 80% being obligate endoparasites or ectoparasites.

subgroups within the platyhelminthes:

Digeneans (trematodes)- flukes

Monogenous - flatworm parasites

Cestodes - tapeworms

Cestodes (tapeworms)

These are endoparasitic tapeworms that live in the intestines of vertebrates. They absorb digested nutrients directly through their bodies.

An important cestode parasite of humans:

The pork tapeworm

What are the distinguishing characteristics of nematodes among helminths?

Nematodes are roundworms - the most diverse helminth group. They can have various life cycles, living as endoparasites of animals and plants.

What structure does Trichinella spiralis form in its host, and how long can it persist?

It forms a nurse cell and can live in host muscle for up to 30 years.

What are hookworms, and how do they infect human hosts?

Hookworms are geohelminths. Eggs pass in feces and hatch into larvae in soil. Larvae penetrate the bare foot skin, migrating to the lungs, then the trachea, and the larva is swallowed, then they attach to the intestines and feed on blood.

What is the conservation or eradication status of the Guinea worm (Dracunculus medinensis)?

It’s been almost driven to extinction.

Describe the lifecycle of Schistosoma mansoni.

Adults live in human intestinal veins. Eggs leave humans through fecesare passed in feces. Then, they hatch and infect snails which release cercariae that penetrate human skin.

How does Schistosoma mansoni harm humans?

Its eggs trigger an immune response that damages the intestines.

How do digeneans demonstrate trophic transmission?

The snail releases cercariae, which infect the fish. Then a bird eats the infected fish. The parasite matures inside the bird into an adult.

How can the pork tapeworm infect humans?

Humans eat undercooked pork contain larvae, making them acquire an intestinal tapeworm infection

Why can the pork tapeworm cause serious neurological disease?

Ingested tapeworm eggs can develop into larvae that lodge in the brain, causing neurocysticercosis, a major cause of epilepsy.

How do humans contract Trichinella spiralis?

By eating raw or undercooked muscle tissue that contains larvae

Ex: Pork

How does Trichinella spiralis maintain a nurse cell?

This changes a skeletal muscle into a nurse cell by breaking down its normal structures

Then, new blood vessels are stimulated to grow, allowing parasite to nourish itself

Why do hairworms manipulate host behavior?

These helminths parasitize arthropods and manipulate their hosts to enter water, allowing them to emerge and become free-living aquatic adults

What unique transmission characteristic sets filarial nematodes apart from other animal parasites?

Filarial nematodes are the only group vectored by insects and transmitted by blood-feeding vectors.

Population

Group of individuals of SAME species living in the same area.

Community

All populations of different species living and interacting in the same area.

Ecosystem

A community of organisms interacting with each other and their nonliving environment.

Population Density

number of individuals in a population per unit area or volume.

Ecological Niche

The role of a species within its community, including the resources it uses and its interactions with other organisms.

Density-dependence

Changes in a population’s characteristics caused by changes in its own population density.

What is an infrapopulation?

All the parasites of the same species living in ONE host

What is a component population?

All parasites of ONE species living in all individuals of ONE host species in a particular area.

What is a suprapopulation?

All parasites of ONE species across all developmental stages and host species within an ecosystem.

What is an infracommunity?

All parasites of ALL species living in ONE individual host.

What is a component community?

All parasites of ALL species living in individuals of ONE host species in a particular area.

What is a supracommunity?

All parasites of ALL species across all developmental stages and host species within an ecosystem

In parasite ecology, how do an infrapopulation, a component population, and a suprapopulation differ?

An infrapopulation consists of all parasites of a single species in an individual host, a component population consists of all parasites of that species across a host population, and a suprapopulation consists of all parasites of that species across all life stages and hosts in an ecosystem.

What is the distinction between parasite prevalence and parasite intensity?

Prevalence is the proportion or percentage of examined hosts that are infected, whereas intensity is the number of parasites living inside a specific infected host.

How do you calculate parasite prevalence?If 5 out of 20 frogs are infected, what is the prevalence?

(Number of infected hosts ÷ Total hosts examined) × 100. (5 ÷ 20) × 100 = 25%.

What is parasite intensity?

The number of individuals of a particular parasite species living in a single infected host.

How do you calculate mean parasite intensity? If three infected hosts have 5, 3, and 1 parasites, what is the mean intensity?

Total number of parasites ÷ Number of infected hosts. → (5 + 3 + 1) ÷ 3 = 3 parasites per infected host.

What is the typical spatial distribution pattern of parasites across hosts in nature?

Parasites typically exhibit an aggregated (clumped) distribution, where most hosts harbor few or no parasites while a small number of hosts harbor the vast majority.

What is the difference between prevalence and intensity?

Prevalence measures the percentage of hosts infected, while intensity measures the number of parasites within an infected host.

How are parasites typically distributed across hosts in nature?

Aggregated distribution.

What is an aggregated distribution?

Most parasites are concentrated in a small number of hosts, while most hosts have few or no parasites.

What causes aggregated parasite distributions?

Some hosts have genes that make them more resistant to parasites than others, so the parasites are more likely to infect the more susceptible host

Why is parasite aggregation important?

It affects parasite transmission, host mortality, and the treatment of human-infective parasites.

What happens to the establishment of new parasite infections as infrapopulation density

Establishment decreases because new parasites have more difficulty establishing within an already infected host.

What happens to parasite growth as infrapopulation density increases?

Parasite growth decreases because parasites compete for limited host resources.

What is parasite fecundity?

The reproductive output of a parasite, such as the number of eggs or offspring produced.

What happens to parasite fecundity as infrapopulation density increases?

Fecundity generally decreases because parasites have fewer resources available for reproduction.

What happens to host survival as infrapopulation density increases?

Host survival generally decreases because higher parasite burdens can cause greater harm to the host.

How is host survival affected as parasite infrapopulation density increases?

Host survival declines due to greater tissue damage, nutrient drain, and pathological burden imposed by higher numbers of parasites.

Micro evolution

Changes in allele frequencies within populations over generations.

macro evolution

Evolution at or above the species level, including speciation.

Co evolution

When two species evolve in response to one another over generations.

adaption

A heritable trait that increases an organism's survival or reproductive success in its environment.

reproductive isolation

When populations can no longer successfully interbreed and exchange genes, allowing them to evolve into separate species.

what is the definition of co-evolution?

Reciprocal evolutionary changes between two interacting species, where each species influences the evolution of the other.

What does it mean that host-parasite coevolution is 'antagonistic'?

It means the host and parasite exert reciprocal selective pressures with conflicting fitness interests, where host adaptations to resist infection select for parasite adaptations to overcome resistance.

How does arms race coevolution differ from Red Queen coevolution?

Arms race coevolution involves directional, escalating adaptations and counter-adaptations, whereas Red Queen coevolution involves continuous, cyclical or fluctuating adaptations where organisms must continuously evolve just to maintain their relative fitness.

How does Trypanosoma brucei demonstrate the principles of Red Queen coevolution?

The parasite is evolving to keep up, and it keeps changing disguises. While the host keeps learning how to recognize the new disguise.

Why do parasite virulence and host resistance evolve toward intermediate 'optimal' levels rather than maximizing infinitely?

Parasite virulence is constrained by transmission trade-offs (killing the host too quickly stops transmission), while host resistance is constrained by the energetic and physiological costs of immune maintenance.

What is cospeciation, and what parasite characteristics make it more likely to occur?

Cospeciation is the parallel speciation of a host and its parasite; it is favored by high host specificity, low parasite dispersal capacity, and vertical transmission between parent and offspring hosts.

Which process appears to be more important for generating parasite species: cospeciation or host-switching?

Host-switch speciation.

what is hose switch speciation ?

When a parasite begins infecting a new host species and becomes reproductively isolated from its original population, eventually forming a new species.

Why might parasites increase a host’s metabolic rate?

Parasites consume host resources, forcing the host to expend more energy to compensate. Immune responses and tissue repair also require additional energy.

Why might parasites decrease a host’s metabolic rate?

Infected hosts may reduce their activity and consume less food, resulting in lower energy expenditure.

Do parasites always increase host metabolic rate?

No. Parasites can increase, decrease, or have no effect on metabolic rate depending on the host and infection.

In what ways can a parasite reduce a host's evolutionary fitness to zero?

A parasite can reduce host fitness to zero either by causing host mortality prior to reproduction or by inducing complete parasitic castration.

How do parasites generally affect host fecundity?

Parasites generally decrease host fecundity by reducing reproductive output.

What are two ways parasites can reduce host fitness to zero?

Killing the host before it reproduces or completely preventing the host from reproducing through parasitic castration.

What is parasitic castration?

When a parasite completely eliminates its host’s ability to reproduce, sometimes by destroying reproductive organs.

Why is parasitic castration an extreme example of reduced fecundity?

Because the parasite completely prevents reproduction, reducing the host’s fecundity to zero.

Why might parasite infection decrease host fecundity?

Parasites consume resources and trigger costly immune responses, leaving the host with less energy for reproduction.

How did parasites affect reproduction in red grouse?

Infected grouse had fewer eggs, lower hatching success, and lower survival than grouse treated with antihelminth medication.

What parasite groups can cause parasitic castration?

Larval trematodes, rhizocephalan barnacles, and certain parasitic isopods.

What is parasite-induced gigantism?

When an infected host grows unusually large, sometimes because resources normally used for reproduction are redirected toward growth.

Why might a snail infected by a parasitic castrator undergo gigantism?

Energy that would normally support reproduction becomes available for body growth, allowing the snail to grow larger.

What is fecundity compensation?

When an infected host increases reproduction early in infection to compensate for expected future reproductive loss.

Why might a snail undergo fecundity compensation after trematode infection?

→ To produce more offspring before the parasite eventually eliminates its ability to reproduce.

How do nematomorphs change the behavioral phenotype of their hosts?

Nematomorphs (hairworms) manipulate infected insects into entering bodies of water, allowing the parasites to complete their lifecycle.

Under what circumstances do parasites reduce host population sizes?

When parasites reduce host survival or reproduction, particularly in combination with environmental factors such as food availability and predation.

How can parasite-mediated competition change the distribution of host species?

When two host species share parasites, the more susceptible species may decline or disappear, allowing the more resistant species to expand.

A naïve host

A naïve host is a host with no previous exposure to a particular parasite and little evolved resistance to it.

How does differential survival and reproduction cause hosts to evolve in response to parasites?

Hosts that resist and survive their parasites are more likely to survive and reproduce, passing their resistance to offspring.

What is a host’s physical phenotype?

The observable physical characteristics or appearance of a host.

How do trematodes change the physical appearance of infected snails?

Leucochloridium paradoxum causes colorful, pulsating structures that form in the snail’s eyestalks, making them attractive to birds.

Why does Leucochloridium alter a snail’s appearance?

To attract birds that eat the infected snail, allowing the trematode to reach its definitive host.

What parasite group does Leucochloridium paradoxum belong to?

Trematodes (parasitic flatworms).

What parasite group does Myrmeconema neotropicum belong to?

Nematodes (roundworms).

What ecological consequence occurred when avian malaria was introduced to naïve bird hosts (honeycreepers) in Hawaii?

Because the naïve honeycreepers lacked evolutionary adaptations against the novel pathogen, avian malaria caused catastrophic mortality, severe population declines, and restricted surviving birds to high-elevation mosquito-free zones.

How did the introduction and eradication of rinderpest in African ungulates demonstrate ecosystem-level impacts of parasites?

Rinderpest decimated wild ungulate herds, which reduced grazing pressure, increased fuel for wildfires, and diminished predator populations; its eradication reversed these changes, restoring herbivore densities and savanna structure.

How does the behavior of nematomorphs (hairworms) alter energy flow through ecosystems?

By driving their terrestrial insect hosts to drown in water, hairworms subsidize aquatic food webs with massive inputs of terrestrial biomass preyed upon by aquatic organisms.

How have malaria parasites altered the genetic diversity of the human hemoglobin gene?

Malaria has acted as a strong selective pressure maintaining polymorphisms (such as the sickle-cell allele) via balancing selection, where heterozygotes possess resistance to severe malaria despite homozygous disadvantages.

What does the Hamilton-Zuk hypothesis predict regarding trait attractiveness and parasite intensity within a host species?

Within a species, individuals with lower parasite infection intensity will be able to produce brighter, more exaggerated, and more attractive sexual display traits.