Tens of thousands of songbirds in the west of Germany have died following an infection with Trichomonas gallinae, and the disease appears to have spread across the border into the eastern Netherlands.

The parasite causes a yellow-coloured swelling in the animal's throat, causing it to die in about four days through starvation or suffocation.

So far, the disease called "canker"or "frounce" in English, and "the yellow" in Dutch, has been confirmed in two greenfinch in the eastern towns of Vriezenveen and Winterswijk. A survey by Dutch birdwatch group SOVON found that collared doves and blackbirds may also have been infected. A nature programme on Dutch public radio reported 101 birds found dead, some of them near the central city of Utrecht.

Veterinary researcher Hugh Jansman of Wageningen University told NRC Handelsblad that the disease is probably caused by a hitherto unknown strain of Trichomonas gallinae, a protozoa that has been found in wild birds. The canker disease was first described as early as 1500, but was not found in wild songbirds until 2002. A milder variant of the disease has been around for much longer, affecting rock doves and birds in aviaries.

"We are checking which of those 101 birds died of trichomoniasis, and we're monitoring how the disease is spreading," Mr Jansman said. Most of the affected birds are greenfinch. The local population, 50 to 100,000 breeding pairs, may be decimated, but there is no risk that the bird could become extinct in the Netherlands, Mr Jansman estimates.

Prevention

Trichomonas gallinae is not able to survive for long on its own outside the host, so the canker can only pass from bird to bird by direct contact. Young birds can catch it when being fed by their parents, birds of prey get it when they eat infected birds. Water in bird baths and feeders can also pass on the protozoa. It is expected that the spread will stop when temperatures fall at the onset of autumn.

The spread of the disease is hard to prevent, but bird protection groups are urging people to regularly clean bird feeders, baths and water troughs using a 10 percent solution of domestic bleach. This should be washed off thoroughly. Birdseed should be kept dry, and wet seeds should be removed from bird feeders. Birds found dead should be reported to SOVON.

T. gallinae does not affect humans, although other members of the Trichomonas family do.

Photo: Fred Vloo
(NRC H, birds.suite101.com, vroegevogels.nl, sovon.nl)