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