WHAT IS MALARIA?
• An infective disease caused by protozoan
parasites that are transmitted through the
bite of an infected Anopheles mosquito;
marked by paroxysms of chills and fever
MALARIA FACTS
•
•
•
•
•
A LITTLE ETYMOLOGY
• The term malaria dates back to the mid
18’th century
• It is credited to the Italian physician
Francesco Torti
• The name means “bad air”
mala = bad and aria = air
MALARIA LIFE CYCLE
Causal agents are Plasmodium sp.
Mosquito vectored (Anopheles sp.)
300,000 new human cases/year
Kills > 700,000/yr
Most victims are children
HOW WE MODEL MALARIA
• Classic approach is to build S.I.R.
models:
– Susceptible
– Infected
– Recovered
IN S.I.R. MODELS
• We classify individuals according to
their state and then use mathematical
functions to determine transition rates
between states (e.g. S ➔ I )
IN S.I.R. MALARIA MODELS
MALARIA MODEL VARIABLES
X
Y
Z
b
α
ν
β
γ
• There are 5 classes, 3 for humans
(S.I.R.) and for mosquitoes (S.I.)
X
Y
b
α
CLASSIC MALARIA
THEORY
… dX
dt
= !"
Y
X + (b + # )Y + (b + $ ) Z
N
Healthy but susceptible
Infected
Recovered and immune
Natural mortality rate
Diseased mortality rate
Recovery rate
Biting rate
Immunity loss rate
N=X+Y+Z
CLASSIC MALARIA
THEORY
…
dX
Y
= ! " X + (b + # )Y + (b + $ ) Z
dt
N
dY
Y
= " X ! (b + # + % )Y
dt
N
CLASSIC MALARIA
THEORY
… dX
dt
= !"
Y
X + (b + # )Y + (b + $ ) Z
N
dY
Y
= " X ! (b + # + % )Y
dt
N
dZ
= %Y ! (b + $ )Z
dt
CLASSIC MALARIA
THEORY
•…
dX
Y
= ! " X + (b + # )Y
dt
N
dY
Y
= " X ! (b + # )Y
dt
N
BASIC REPRODUCTIVE RATE
N
!2
N
R0 =
b
+
"
+
b
(
) ( +" +#)
VECTORIAL CAPACITY
m! 2 " n
C=
# ln "
Where: m = mosquito/human ratio, β = biting
frequency, p = survival, n = length of cycle
VECTORIAL CAPACITY
ANOPHELES BIOLOGY
m! 2 " n
C=
# ln "
Where: m = mosquito/human ratio, β = biting
frequency, p = survival, n = length of cycle
PREDIURESIS
MOSQUITO NUTRITIONAL
ECOLOGY
• What mosquitoes eat and why
SOME “FACTS”
• Mosquitoes feed on sugar to maintain
somatic (body) function
• Mosquitoes feed on blood for gametic
(reproduction) function
• Sugar feeding trades off with blood
feeding
• Sugar feeding impacts survivorship
and blood feeding
WHAT ABOUT SUGAR?
• The conclusion:
• Plant feeding is rare and trivial for An.
gambiae (and other mosquitoes closely
associated with humans)
BUT
• There are lots of reasons to believe
otherwise
AND!!!
• Nearly every mosquito lab that I know of
provides sugar to adult mosquitoes. WHY?
WHAT ABOUT SUGAR?
• The word on the street:
– An. gambiae can allocate energy
from human blood to soma
– Nectar feeding is rarely observed
– Fructose-positive samples are not
common (e.g. 20% Beier 1996)
WHAT ABOUT SUGAR?
• BUT:
• Without knowing sugar digestion rates,
frequency of fructose positivity is
meaningless
• Behaviors that are not frequently
expressed are not necessarily trivial
• Feeding on humans is dangerous
VECTORIAL CAPACITY
m! 2 " n
C=
# ln "
Where: m = mosquito/human ratio, β = biting
frequency, p = survival, n = length of cycle
ENERGY PROFILES IN
NATURE
LIFE IS TOUGH
Reserves
• Energy is in short supply for
Anopheles.
TWO MORE FACTS
• Under nutrient stress, female
mosquitoes reallocate resources away
from survival and towards
reproduction
• Nutrition state can affect the impact of
Plasmodium on female survival
CONTROLLED EXPERIMENT
• Give female mosquitoes
choice of blood host and
nectar host odors
THE SMOKING GUNS
•
•
•
•
Observations
Crop collections
Digestion rates
Frequency estimates
A CLEAR PREFERENCE
CLASSIC ASSUMPTION
AN OBSERVATION
• Everybody is plastic
• Mosquito behavior is hardwired and
invariant
• Recall, we assumed that beta was a
constant but if sugar alters beta then it
isn’t
VARIABILITY IN NATURE
• …
HOW TO EXPLOIT ENERGY
VARIABILITY IN NATURE
• Employ bednets in the context of
mosquito energy budget
constraints….
A MINI VILLAGE
• …
TESTING THE THEORY
• •Our
…. mini domicile
HOW TO EXPLOIT ENERGY
VARIABILITY IN NATURE
• Employ bednets in the context of mosquito
energy budget constraints
TESTING THE THEORY
Energy state effects
!
TESTING THE THEORY
• Semi field conditions
TESTING THE THEORY
• Semi field conditions