DISEASE E&E (Transmission 2)

Question 1

Indirect horizontal transmission:

Answer 1

-occurs whenever horizontal transmission of the pathogen between two hosts of the same species requires another organism

Question 2

Vector-borne life cycles:

Answer 2

-require an arthropod vector and a vertebrate host

Question 3

Complex life cycles of helminth parasites:

Answer 3

-require an intermediate host and final host

Question 4

Vector-borne diseases:

Answer 4

-caused by vector-borne pathogens that are transmitted among vertebrate hosts by hematophagous (blood-feeding) arthropod vectors

Question 5

Examples of important arthropod vectors:

Answer 5

-mosquitoes
-ticks
-sandflies
-assassin bugs

Question 6

When do arthropod vectors transmit the vector-borne pathogens?

Answer 6

-during the blood meal

Question 7

Vector-borne pathogen (VBP) examples:

Answer 7

-viruses
-bacteria
-protozoan parasites
-nematode worms

Question 8

Vector-born pathogens lifecycle 2 critical steps:

Answer 8

1. Uninfected vectors must acquire VBP from an infected vertebrate host
2. Infected vectors must transmit the VBP to other uninfected hosts

Question 9

Condition of vector-borne transmission:

Answer 9

-vector must take at least 2 blood meals on different vertebrate hosts

Question 10

Dengue virus life cycle example:

Answer 10

-mosquitos=vector
-humans=host
1. Human-to-mosquito transmission: uninfected mosquito feeds on infected human and acquires Dengue
2. Mosquito-to-human transmission: infectious mosquitos bites an uninfected human and human becomes infected

Question 11

Vector becomes infectious:

Answer 11

*vector is not immediately infected after feeding on an infected host
-need to migrate the pathogen from the midgut to the salivary glands (can take days or weeks)
-in salivary glands=infectious

Question 12

EIP:

Answer 12

-time for a vector to become infectious after feeding on infected host

Question 13

Temperature and EIP:

Answer 13

-influences the rate at which vectors become infectious

Question 14

High temperature on EIP:

Answer 14

-increase pathogen replication and migration
-higher abundance of infectious vectors
*shorter EIP

Question 15

Pros of VB life cycle:

Answer 15

-motivated vector: hematophagous arthropods are motivated to seek out new hosts
-dispersal: winged arthropods can travel distances and contact new hosts
-one infected host can produce many infected arthropod vectors

Question 16

Cons of VB life cycle:

Answer 16

-evolve ability to live in both arthropod vector and vertebrate host
-infected vector may feed on ‘wrong’ vertebrate host

Question 17

West Nile fever:

Answer 17

-mosquito-borne disease
-an RNA virus
-birds: reservoir hosts
-mammals: dead-end hosts

Question 18

Reservoir hosts:

Answer 18

-competent hosts
Ex. birds with high viremia (WNV) have high host-to-mosquito transmission

Question 19

Dead-end hosts:

Answer 19

-incompetent hosts
Ex. mammals have low levels of WNV in their blood (ex. low viremia)
>WN doesn’t want to be in a mammal

Question 20

Low vs. high viremia when mosquitoes feed on infected birds:

Answer 20

-low: fewer mosquitoes acquire WNV
-high: most mosquitoes acquire WNV
*high viremia in birds, increases chance of WNV transmission to feeding mosquitoes

Question 21

Infection with WNV mortality:

Answer 21

*can kill both reservoir and dead-end hosts and also be asymptomatic
-high in birds
-outbreaks recognized in crows
-40% mortality in horses
-humans are asymptomatic
*mortality and morbidity are not good predictors of host competence

Question 22

“bridge” vector:

Answer 22

-connects reservoir host (birds) and the dead-end hosts of interest (humans and humans)
Ex. have 2 species that prefer bird blood but will do 20% of their blood from mammals

Question 23

Vector competence:

Answer 23

-the ability of a vector to transmit a disease
-occurs because VBP have evolved to become adapted to certain species of arthropod vectors

Question 24

Vector competence comprises of:

Answer 24

1. Capacity of vector to be infected
2. Maintain and transmit an infectious agent

Question 25

Vector competence ticks:

Answer 25

-few spirochetes: unable to transmit Lyme disease (D. variabillis, A. Americanum) -I. scapularis: high

Question 26

Complex life cycle (macroparasites):

Answer 26

-carried by one or more intermediate hosts (invertebrate or vertebrate) and one final vertebrate host -sexual reproduction often takes place in final vertebrate host -results in shedding of an infectious stage into the environment -eggs hatch and resultant life stages infect the intermediate host

Question 27

Food chains (complex life cycle):

Answer 27

-facilitate tropic transmission of parasites form intermediate hosts to predators

Question 28

Type of hosts (complex life cycle):

Answer 28

-final or definitive host -intermediate host

Question 29

Final or definitive host:

Answer 29

-organism in which parasite reaches maturity and reproduces sexually

Question 30

Intermediate host:

Answer 30

-organism that harbors the immature stages of the parasite -required by the parasite to undergo development and compete its life cycle

Question 31

Types of helminths (parasitic worms):

Answer 31

-roundworms -flukes -tapeworms -thorny-headed worms

Question 32

Parasitic roundworms and direct life cycles:

Answer 32

-infective L3 larvae eaten by vertebrate host: develop into adult worms -adult worms produce fertilized eggs expelled into fecal matter -eggs hatch in dung -L3 move onto pasture and cycle continues *direct=one-species *roundworm larvae spend lots of time in the environment

Question 33

Fasciolosis in livestock:

Answer 33

-common liver fluke -complex lifecycle: final vertebrate host and intermediate snail host -adult worms in liver produce eggs -miracidia and cercariae

Question 34

Miracidia (fasciolosis):

Answer 34

-infect snails and develop into free-swimming cercariae

Question 35

Cercariae (fasciolosis):

Answer 35

-encyst on water plants and are ingested by vertebrate hosts

Question 36

Is FMDB a complex life cycle?

Answer 36

-no -it is NOT REQUIRED to have a second host

Question 37

Life cycle of tapeworm: Echinococcus multilocularis

Answer 37

-complex -final and intermediate hosts are canids and rodents -adult host lives in small intestine of the definitive host and produces eggs -intermediate host (rodent) ingests eggs -eggs hatch in small intestine and release oncosphere that targets liver

Question 38

Oncosphere (echinococcus)

Answer 38

-develops into cyst, which grows over time and produces protoscolices -dog eats mouse and protoscolices develop into adult worms

Question 39

Cysts replace tissues in liver (echinococcus):

Answer 39

-organ will lose it’s function

Question 40

If dog or human ingests tapeworm egg (echinococcus):

Answer 40

-it will treat the dog or human as an intermediate host

Question 41

Alveolar echinococcosis:

Answer 41

-if dog or humans consumes eggs, tapeworm will treat them as intermediate host -eggs hatch into oncosphere that develops cysts in liver -growing cysts in liver will kill patient because organ stops functioning *tapeworm cannot skip steps in its complex cycle

Question 42

How could cysts in dog complete life cycle (echinococcus);

Answer 42

-dog would need to die and be consumed

Question 43

Cons of a complex life cycle:

Answer 43

-evolve ability to make a living in many different hosts -expect probability of completing a life cycle to decrease with number of hosts

Question 44

Host size and trophic level vs. helminth life-cycle length:

Answer 44

-host mass increased along the links of the parasite life cycle -host tropic level increased along the links of the parasite life cycle

Question 45

Size of final host and adult parasite vs. life-cycle length:

Answer 45

-final host was larger in helminth life cycles with more hosts -adult parasites were larger in helminth lifecycle with more hosts

Question 46

Advantages of a helminth life cycle with more hosts:

Answer 46

1. First hosts are small and numerous and easy to find 2. Final hosts are larger, longer-lived endotherms that allow bigger adult body size >Bigger female worms produce more offspring

Question 47

Advantages of adding a predator to the lifecycle:

Answer 47

-bigger host=more resources -longer-lived=more time to reproduce -parasite can grow larger=produce more offspring *adding the predator offsets losses due to predation

Question 48

Advantages of adding a prey host to the lifecycle:

Answer 48

-predators are unlikely to ingest immature stages (ex. eggs) in the environment -prey more common=easier to encounter -prey more likely to feed on immature stages -high predation rates concentrate parasite into original predator host

Question 49

Trophic transmission:

Answer 49

-highly efficient because food webs are ubiquitous in nature -predators encounter prey frequently -infecting prey is a great way to meet a predator -delay sexual maturation until you reach your final host: have space and a long life