Lecture 21

Question 1

pathogen

Answer 1

• causative agent of disease

o Virus, bacteria, fungi, protozoa, etc.

Question 2

host

Answer 2

• living organism from which a parasite obtains nutrition; in which the pathogen will grow
o Plant or animal

Question 3

vector

Answer 3

• organism that transmits a pathogen

o Aphid, mosquito, flea, tick etc.

Question 4

what are the 3 requirements for vector disease to occur?

Answer 4

pathogen, host & vector all occurring together in time & space

Question 5

What are the 2 methods of transmission?

Answer 5

Mechanical & biological

Question 6

how do insects usually transmit disease?

Answer 6

usually through feeding

Question 7

mechanical transmission

Answer 7

Simple transfer of pathogen, “a flying needle”

Not alive, structure that facilitates transfer

Question 8

what are exs of mechanical transmission

Answer 8

Ex: aphid – exerts stylet into tissue of plant to feed on phloem & the virus from the infected plant sticks to the stylet
When the aphid feeds on other plants, the virus will be transmitted

Ex: Mouthparts (labellum) & “foot” (tarsus) of a house fly – lots of places for bacteria to hide
Ex: hairs on feet

Question 9

biological transmission

Answer 9

Multiplication, reproduction &/or development of the pathogen in the vector

Question 10

extrinsic incubation period

Answer 10

from infective blood meal to transmission

Mosquito feeds on blood & takes in virus 

Pathogen reproduces & multiples in the gut of the mosquito 

Only after this time, the mosquito can transmit the virus 

     Certain amount of time b/w contamination & transmission

Question 11

the plague pathogen _____ in the vector

Answer 11

multiplies

Question 12

what is the host, vector & pathogen of the plague?

Answer 12

Pathogen: bacteria, Yersinia pestis

Vector: flea (Oriental Rat Flea) Xenopsylla cheopis

Host: rodents (wild or domestic), humans

Question 13

sylvatic cycle

Answer 13

occurring in or affecting wild animals

Question 14

bubonic plague

Answer 14

through direct contact (rodent & human) or contact of people with the rodent fleas humans receive pathogen

Question 15

pneumonic plague

Answer 15

easily transmitted, air borne (coughing) method of transmission from human-human (leads to an epidemic)

Question 16

what are the 3 plagues included in the sylvatic cycle?

Answer 16

bubonic plague

pneumonic plague

urban cycle

Question 17

what type of transmission takes no time?

Answer 17

mechanical

Question 18

what type of transmission takes time?

Answer 18

biological

Question 19

when did people begin to understand what was occurring with the plague?

Answer 19

the 3rd pandemic

Question 20

who were the 2 scientists who discovered that the causative agent of the plague was bacteria?

Answer 20

Yersin & Kitasato

Question 21

Koch’s postulate

Answer 21

1. Isolate the agent
2. Culture/purify the agent
3. Inoculate uninfected host
4. Re-isolate agent

Question 22

Filariasis

Answer 22

infestation of worms that block the lymphatic sys & leads to swelling

Question 23

what was believed caused Filariasis?

Answer 23

Worms in mosquitos were much larger

Believed that the big worms (mother worms) got into humans through a bite

Question 24

describe how a flea acquires the plague pathogen

Answer 24

Flea ingests blood, spines in the proventriculus break blood cells down to digest

When a flea begins to feed on infected blood

Bacteria will grow & multiple in the proventriculus 

As the blood is digested the bacteria continue to multiple 

Leads to a big plug of bacteria that plugs the proventriculus & prevents digestion

Flea gets hungry b/c it can’t digest the blood so it keeps feeding 

Bites repeatedly, will feed on blood, but it regurgitates blood b/c of the bacteria plug

Question 25

describe the pathogen, vector & host of malaria

Answer 25

Pathogen: protozoa, Plasmodium sp.
Sexual reproduction

Vector: mosquito, Anopheles sp.

Host: human (but not only)

Question 26

malaria is an ex of what kind of transmission?

Answer 26

biological

Question 27

describe what occurs in the mosquito during the transmission of malaria

Answer 27

Male & female Plasmodium reproductive cells form a zygote

Zygote passes through mosquito midgut (in hemplymph) to form an oocyst (egg), from where sporozoites emerge; sporozoites migrate & invade salivary glands => sporozoites injected when mosquito feeds on human

Mosquitos have anticoagulant to prevent blood clotting & maintain blood flow

The anticoagulant contains that pathogen

Question 28

What are factors influencing transmission of pathogens? (5)

Answer 28

Host location ability

host preference

feeding mechanism

vector susceptibility

envr

Question 29

what type of vectors look for host location ability with colours, movement & size ?

Answer 29

daytime biters

Question 30

what type of vectors look for host location ability with heat, convection & currents ?

Answer 30

nighttime feeders

Question 31

describe how vector susceptibility influences transmission of pathogens

Answer 31

incubation period, sometimes the vector is not a suitable envr for reproduction & replication

Question 32

describe how the envr influences transmission of pathogens

Answer 32

colder temps takes longer time to develop, vector can die before transmission

Question 33

what is an ex of how climate change influenced the transmission of pathogens & what was the result?

Answer 33

bluetongue virus

Strains from Africa moved into Europe
- C. imicola moved north & introduced the pathogen