Syringes with a natural aptitude for sucking blood

Another version of this article first appeared on The Scientist Magazine: Notebook.

 

SOP of collecting blood from birds: Pricking a vein with a needle and collect the blood with  a microcapillary tube. [credit: maddyincameroon.wordpress.com]

SOP of collecting blood from birds: Pricking a vein with a needle and collect the blood with a microcapillary tube. [credit: maddyincameroon.wordpress.com]

A decade ago, Dr. Peter Becker, who studies birds at the Institute of Avian Research, Germany, attended a seminar on bats and blood-sucking bugs. What he heard that day sparked an idea that solved his long-standing problem—how to collect blood from birds without trapping and handling them.

Scientists often draw blood samples from animals. Blood analyses provide much information—cell counts, hormone levels, pathogen loads, proteins etc.—that help scientists better understand the animals.

But nobody likes syringes. Most animals, especially wild ones, would have to be subdued by anesthetics or force. Either way stresses the animals and tampers with blood analyses.

“Stress-sensitive parameters like the hormone corticosterone rise quickly” in stressed birds, says Becker. “If one is not able to bleed them within three minutes, one cannot measure baseline levels (of hormones).”

When normal syringes failed, bat scientists turned to living syringes: blood-sucking assassin bugs of the subfamily Triatominae found in the Americas. In 1986, scientists had demonstrated that these bugs could suck blood from bat wings without alerting the bats; the bat blood could then be collected from the swollen abdomens of the blood-fed bugs.

These assassin bugs easily outperform our syringes. They have needle-like mouths that are more than 30-times thinner than the usual syringes used for drawing blood. The bug’s saliva also anaesthetizes the feeding site and promotes blood flow.

Birds spend much time incubating eggs. Becker wondered: if the bugs could be placed into hollow, perforated eggs, and those eggs smuggled into the nests, couldn’t the bugs suck the bird’s blood and be retrieved with the dummy-eggs later when the birds have left the nest?

“I thought if that works it is a great idea,” recalls Becker “it will definitely disturb breeding birds less than if one needs to catch them.”

Becker worked on the dummy-egg design. “One of the first challenges was the weight of the dummy-egg,” says Becker. The bugs grip their hosts during feeding; if the egg is too light and the bird move while the bug is feeding, “the egg may stick to the bird and be displaced from the nesting area.”  He made the eggs out of epoxy casting resin, and weighed down the eggs with metal within.

The birds tend to roll their eggs.  The initial dummy-eggs had one netted window, which would sometimes face away from the bird when the eggs were rolled. Becker changed the window to many little holes around the circumference of the eggs; the bugs feed through the holes.

Kissing bugs are placed within these artificial eggs, and the eggs deposited into bird nests alongside the real eggs. When the bird returns to the nest, the bugs can reach through the holes on the artificial eggs to suck the bird's blood. [credit: Christina Bauch]

Kissing bugs are placed within these artificial eggs, and the eggs deposited into bird nests alongside the real eggs. When the bird returns to the nest, the bugs can reach through the holes on the artificial eggs to suck the bird’s blood. [credit: Christina Bauch]

Becker tested the dummy-eggs on Common Terns (Sterna hirundo), using the triatomine bug Dipetalogaster maximus. “Even our first approaches were successful,” beamed Becker: one-third of dummy-egg trials collected enough blood for analysis. Becker’s lab continued to improve the egg design. Current blood sampling rates are above 80%. Becker can now sample blood of Common Terns, even during breeding seasons, for long-term studies.

Not everyone likes bugs. “It was a little scary to see about a hundred bugs running in a little glass jar,” describes Dr. Christina Bauch who employed dummy-eggs to study Common Swifts. Fortunately, “extracting blood from the bugs is easy”. The swollen abdomen of the blood-fed bug is punctured with a syringe and the blood is drawn out “carefully and slowly”.

The ingested blood in the bug remains undigested if it is extracted within hours. The bugs store blood in its crop before minor dilution and small nutrient absorption start hours later, explains insect physiologist Dr. Fernando Genta of Instituto Oswaldo Cruz, Brazil. It would take days and weeks for ingested blood to move into the midgut to be digested. Numerous studies found no differences in hormones, blood chemistry and antibody titres between the blood collected with syringes and bugs.

Generalized diagram of insect digestive system.  Food eaten by the insect is first kept in the crop, then moved to the midgut for digestion. [modified from Gullan & Cranston]

Generalized diagram of insect digestive system. Food eaten by the insect is first kept in the crop, then moved to the midgut for digestion. [modified from Gullan & Cranston]

Genta assures that possible contamination of the ingested blood with insect or microorganism sources “can be easily discriminated” by using “specific probes for the genetic material of the blood host.” Telomere studies, which require samples of high quality DNA, have been conducted with blood collected by triatomine bugs.

Scientists have used triatomine bugs to collect blood of more than 40 species of animals. But because triatomine bugs are vectors of a parasite that cause the Chagas disease, triatomine bugs are used mostly in captivity in temperate regions, without a single field application in the tropics.

“I would not want to introduce triatomine bugs to Africa,” says Dr. Wolfgang Goymann of Max Planck Institute for Ornithology, who studies birds in Tanzania and have tested triatomine bugs in captivity. “If they get loose, (who) knows what could happen. They could become new vectors for diseases affecting wild animals and humans.”

Dr. Gunter Schaub of Ruhr-Universität Bochum, Germany, who supplied triatomine bugs to labs in Europe, agrees with Goymann. He suggests that scientists focus on searching “for a factor that kills the bugs during its next molt, avoiding establishment in the tropical regions.”

Becker will continue to use dummy-eggs in his long-term bird studies, though he concedes that sometimes at conferences “there are more questions on the bug method and how great it is than” on the actual study itself. Well, that is the price one pays for a creative solution.

Sources

  1. Bauch, C., Wellbrock, A.H.J., Nagel, R., Rozman, J., and Witte, K. (2013). “Bug-eggs” for Common Swifts and other small birds: minimally-invasive and stress-free blood sampling during incubation. Journal of Ornithology 154, 581–585.
  2. Becker, P.H., Voigt, C.C., Arnold, J.M., and Nagel, R. (2006). A non-invasive technique to bleed incubating birds without trapping: a blood-sucking bug in a hollow egg. Journal of Ornithology 147, 115–118.

Have something to share?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s