Lecture 5: Transmission of Diseases

Question 1

Modes of infectious disease transmission

Answer 1

• Direct contact with pathogen (vector borne diseases)
• Ingestion of pathogen
• Inhalations of pathogen from air

Question 2

Vector

Answer 2

Invertebrate serves as a mechanism to transport the pathogen to a host

Question 3

Transmission efficiency

Answer 3

The rate at which pathogens are transmitted from invertebrate host
-Influenced by: environmental factors, weather, infection rates, insect life history

Question 4

Mechanical transmission

Answer 4

Pathogen does not biologically interact with the arthropod

“hitching a ride” often on the mouth

Question 5

Biological transmission

Answer 5

• Pathogens depend on arthropod as part of life cycle and for transmission
• Propagative, cyclo-developmental, cyclo-propagative

Question 6

Propagative transmission

Answer 6

When the pathogen simply propagates (reproduces) within the arthropod

Question 7

Cyclo-developmental transmission

Answer 7

Seen only in parasites, where the parasite must be in the arthropod host to complete part of its life cycle

Question 8

Cyclo-propagative transmission

Answer 8

Pathogen both completes a developmental stage and can propagate within the arthropod

Question 9

Trans-ovarial transmission

Answer 9

• Vertical transmission occurs when pathogens are passed from a parent arthropod to offspring (TOT)
• Females infect eggs during any part of egg development
• Males infect offspring with infected sperm

Question 10

Trans-stadial transmission

Answer 10

• Transmission of a disease within the same organism from one developmental stage to the next
• Molting, Metamorphosis, Pupation

Question 11

Horizontal transmission

Answer 11

Disease travels from one arthropod to another via a vertebrate host
(ex: cofeeding)

Question 12

Pathogen in the vector

Answer 12

-Often ingested by vector, multiplies in midgut, infects salivary glands

Question 13

Barriers

Answer 13

• Limit transmission
• Physical: lining of midgut, body cavity
• Chemical: chemical or immune responses that may limit or prevent virus from disseminating

Question 14

How do diseases enter the host

Answer 14

• Passive transfer

- Active transfer

Question 15

Passive transfer

Answer 15

Pathogen is transmitted from the vector to the host via some mechanism involving the vector
-commonly through saliva, sometimes feces or regurgitation

Question 16

Active transfer

Answer 16

Some pathogens rely on the host destroying/crushing the body of the vector, releasing the pathogen

Question 17

Incubation period

Answer 17

Time from when an organism ingests the pathogen to when it is capable of transmitting it

Question 18

Intrinsic incubation period

Answer 18

From when the host becomes infected to when it can transmit the pathogen

Question 19

Extrinsic incubation period

Answer 19

From when the vector ingests the pathogen to when it can transmit

Question 20

Primary transmission cycle

Answer 20

Transmission that occurs under natural settings which is essential to the survival and continued transmission of the pathogen

Question 21

Enzootic transmission

Answer 21

• The vertebrate host in primary transmission is an animal

- May serve as “reservoir” for long term survival of the pathogen

Question 22

Dead end hosts

Answer 22

Transmission cycle will stop

Question 23

Epidemic transmission

Answer 23

Can refer to any transmission that involves a human host

Question 24

Disease amplification

Answer 24

Rapid increase in prevalence of a pathogen over a short period of time under specific conditions

Question 25

Arboviruses

Answer 25

• Febrile, hemorrhagic, or neuropathic effects (many share common “flu-like” symptoms)
• Mild infection to severe encephalitis to death

Question 26

Rickettsiae

Answer 26

• Genus of ancient bacteria
• Almost always involves hematophagous arthropods
• Frequently transmitted via TOT
• Often lethal; all (except typhus) involved in enzootic transmission cycle

Question 27

Bacteria

Answer 27

• Only a few involved in arthropod transmission cycles (mostly mechanical)
• Biologically by hematophagous arthopods
• Antibiotics

Question 28

Protozoa

Answer 28

• Sporozoans and flagellates may utilize arthropods for transmission
• Produce serious, widespread epidemics
• Complex life cycles and transmission patterns
• Most transmitted in the salivary glands
• Most cycles are enzootic, but some use humans

Question 29

Helminths

Answer 29

• Develop in arthropod, but do not reproduce there

- Usually not fatal