Lyme Disease Flashcards
dead end host
a host from which infectious agents are not transmitted to other susceptible hosts
(infected human can’t transmit the disease to other unaffected ticks = level of bacteria circulating in blood = too low)
ecosystem service
the quantifiable services than an ecosystem provides to humans
lyme disease
zoonotic disease vectored by ticks - small mammals are the main reservoir species
what bacteria cause LD
spirochete bacteria
gram-negative
even though there are a number of animals hosts for the pathogen what is the main reservoir
mice
what is the vector for the disease
ticks
what do ticks need to do in their lives
need to malt between different life stages
what must a tick do to become infected
feed on an infected host (not human)
what are LD symptoms
within a few days: skin rash after bite
days/weeks: fatigue, chills, fever, headache, muscle/joint aches (due to inflammation), swollen lymph nodes, Bell’s Palsy
long term neurological problems: problems with concentration, short-term memory loss, severe arthritis/joint pain
what happens once the bacteria enter the BBB
enter the brain - harder to treat as harder to reach
what must happen for human outbreak of LD to occur
human must be bitten by infected ticks = need lots of ticks = need to feed on infected hosts
is LD treatable if so with what
the earlier you catch it the easier it is to treat - treated by antibiotics - not beta-lactam as gram-negative bacteria
what are vertebrate hosts for larval and nymphal ticks
rodents, lizards, birds
what are hosts for adult ticks
deer
how do you get infected by LD
bacteria found in salivary glands of a tick, enter the body at the site of the bite (compounds in ticks saliva = suppress the immune system), bacteria then migrate out of site of the bite
how would you recognize LD
distinctive rash - inflammatory response of the body
who has chronic LD
largely in people who have had LD - treated and no longer test positive = treatment worked but still have symptoms
what are 3 explanations of chronic LD
- hidden infection - (not positive)
- autoimmune response - (triggered by initial infection)
- something else (psychological factors/immune system problems)
what is the problem associated with chronic LD
no evidence: symptoms of chronic LD being caused by bacteria - people convinced of hidden infection = want treatment > long term antibiotics (evolution)
if you increase the awareness of a disease
people are more likely to get tested - as science develops, advanced way of testing = increase in no of cases
how and when did we discover LD
1921 - joint problems associated with ticks
1975 - cluster of cases of rashes/swollen joints in Lyme
1982 - bacteria discovered
could the medical establishment do anything in regards to antibiotic misuse
cannot do anything to doctors even if they are harming the patient
what is required for an increase in tick density
heavy acorn production > increase in mice and deer
what happen in the 1960s
Watts riot LA (1965) and Detroit riot (1967) = people left city for suburbs - lots of farmland/contact with animals
what happen when there was a change in land use
reduction of predators = increase in deer = increase in tick density = increase in contact with ticks = LD outbreak
what are ticks and what do they do to survive
arthropods - malt between different life stages and feed on blood
are tick born infected
no but they maintain the infection between life stages
explain the tick life cycle
larvae hatch from eggs take meal > nymphs hatch take meal > adult takes meal
how do ticks detect good hosts
heat and CO2
adult ticks are noticeable but nymphs are not what is the danger
harder to detect to eye as they are tiny = can be infected
differences between LD on East/West Coast
- different tick species
- different host community
- different timing of life cycle (2vs3)
why is the larval stage feeding the most important
one chance to pick up Borrelia infection before nymphal stage
what does the host for tick larval stage determine
nymphal infection prevalence
what feed are humans at risk
nymphal stage feeding
the risk to humans is determined by:
- density of nymphal ticks
- infection prevalence in nymphal ticks
- human behaviour (walk through vegetation/animals bring back ticks)
describe the tick life cycle in the East coast
infected nymphs feed in spring = infect small birds and mammals
larvae feed in summer = infected from previous year
describe the tick life cycle in the West coast
nymphs and larvae both feed in spring = reduce risk of LD - less infected
how can altering the host community affect the disease risk
can either increase (amplification)
or
decrease (dilution)
amplification
adding a species to a community increases the total abundance of hosts for a pathogen = increasing the disease risk to the target host
dilution
adding a species to a community decreases the abundance of competent hosts = decreasing the disease risk to the target host
competence (for hosts)
the efficiency with which a host acquires and spreads a pathogen
as humans move into an area
decrease in different species - community becomes simpler - easier for ticks to replicate (in the northeast more nymphs)
what happens in the east coast as other species are lost
white-footed mice do well
are preferred host of the ticks = more ticks
are a competent host = more infected ticks
what is reservoir competence
hosts differ in their efficiency at acquiring and spreading borrelia spirochete
which host is highly competent
mice
which host is somewhat competent
deer mouse
which host is totally incompetent
western fence lizard
are lizards good hosts
yes but not competent host
why are cases for LD so low in CA
lizards can’t transmit the disease
when an infected tick bites lizard = leaves uninfected = have complementary protein = destroys bacteria and cleanses tick of infection
what are some human behaviours that increase LD risk
leaning against a log
carrying wood
sitting on a log
