Round Trip Ticket
Asystole

I'm Plasmodium, travelling light,
With two hosts booked for a very long ride.
A female Anopheles offers a lift—
One little bite and the scenery shifts.

Sporozoites enter and head for the liver,
Inside hepatocytes, more to deliver.
Liver schizonts release merozoites to go,
Into red blood cells, where our numbers grow.
Ring to trophozoite, schizont, release,
More merozoites; the blood rounds increase.
Some become gametocytes, waiting in line
For another mosquito at blood-meal time.

Liver, then blood, then out with a bite,
Two hosts keep the circle turning tonight.
Sporozoites enter; merozoites invade,
Gametocytes wait for the trip to be made.
Round trip ticket, a parasitic plan—
Mosquito to human and back again.

Blood-stage rupture raises the alarm,
Cytokines bring fever, chills and harm.
Lost red cells help anaemia grow;
The fever can be irregular in its show.
Vivax and ovale can leave behind
Hypnozoites in the liver, biding their time.
Weeks or years later, blood stages can rise:
Relapse from the liver, a delayed surprise.

Liver, then blood, then out with a bite—
Two hosts keep the circle turning tonight.

Falciparum says, "Here's my disguise:
Switch var expression, a new coat to your eyes.
P-f-E-M-P one on the infected red cell
Helps it stick to vessel walls as well.
Sequestration helps us evade the spleen,
With dangerous effects on the bloodstream scene.
Changing surface antigens can slow recognition—
A different little coat for the next expedition."

In the mosquito, gametes meet,
A zygote forms; the next stage takes the street.
Ookinete crosses the midgut wall,
An oocyst grows, then sporozoites call.
Off to the salivary glands for the ride,
Ready for the next human on the other side.
Sexual fusion in the mosquito's stay;
Human stages multiply the asexual way.

Liver, then blood, then out with a bite,
Two hosts keep the circle turning tonight.
Sporozoites enter; merozoites invade,
Gametocytes wait for the trip to be made.
Round trip ticket, a parasitic plan—
Mosquito to human and back again.

Humans break the circle with prevention and care.
My round trip ticket won't take me everywhere.