Lecture 21 Flashcards
pathogen
• causative agent of disease
o Virus, bacteria, fungi, protozoa, etc.
host
• living organism from which a parasite obtains nutrition; in which the pathogen will grow
o Plant or animal
vector
• organism that transmits a pathogen
o Aphid, mosquito, flea, tick etc.
what are the 3 requirements for vector disease to occur?
pathogen, host & vector all occurring together in time & space
What are the 2 methods of transmission?
Mechanical & biological
how do insects usually transmit disease?
usually through feeding
mechanical transmission
Simple transfer of pathogen, “a flying needle”
Not alive, structure that facilitates transfer
what are exs of mechanical transmission
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
biological transmission
Multiplication, reproduction &/or development of the pathogen in the vector
extrinsic incubation period
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
the plague pathogen _____ in the vector
multiplies
what is the host, vector & pathogen of the plague?
Pathogen: bacteria, Yersinia pestis
Vector: flea (Oriental Rat Flea) Xenopsylla cheopis
Host: rodents (wild or domestic), humans
sylvatic cycle
occurring in or affecting wild animals
bubonic plague
through direct contact (rodent & human) or contact of people with the rodent fleas humans receive pathogen
pneumonic plague
easily transmitted, air borne (coughing) method of transmission from human-human (leads to an epidemic)
what are the 3 plagues included in the sylvatic cycle?
bubonic plague
pneumonic plague
urban cycle
what type of transmission takes no time?
mechanical
what type of transmission takes time?
biological
when did people begin to understand what was occurring with the plague?
the 3rd pandemic
who were the 2 scientists who discovered that the causative agent of the plague was bacteria?
Yersin & Kitasato
Koch’s postulate
- Isolate the agent
- Culture/purify the agent
- Inoculate uninfected host
- Re-isolate agent
Filariasis
infestation of worms that block the lymphatic sys & leads to swelling
what was believed caused Filariasis?
Worms in mosquitos were much larger
Believed that the big worms (mother worms) got into humans through a bite
describe how a flea acquires the plague pathogen
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
describe the pathogen, vector & host of malaria
Pathogen: protozoa, Plasmodium sp.
Sexual reproduction
Vector: mosquito, Anopheles sp.
Host: human (but not only)
malaria is an ex of what kind of transmission?
biological
describe what occurs in the mosquito during the transmission of malaria
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
What are factors influencing transmission of pathogens? (5)
Host location ability
host preference
feeding mechanism
vector susceptibility
envr
what type of vectors look for host location ability with colours, movement & size ?
daytime biters
what type of vectors look for host location ability with heat, convection & currents ?
nighttime feeders
describe how vector susceptibility influences transmission of pathogens
incubation period, sometimes the vector is not a suitable envr for reproduction & replication
describe how the envr influences transmission of pathogens
colder temps takes longer time to develop, vector can die before transmission
what is an ex of how climate change influenced the transmission of pathogens & what was the result?
bluetongue virus
Strains from Africa moved into Europe
- C. imicola moved north & introduced the pathogen
