This is an underestimated problem for a lot of pigeon fanciers. We mainly see a contamination of roundworms (Ascaridia columbae) and/or hairworms (Capillaria spp.). The roundworm can sometimes be spotted in the droppings as thin spaghetti strings. These worms attach to the first part of the intestinal tract and can constipate the duodenum by their numerous presence. Mostly they cause a chronic loss of weight and condition.
Unlike the roundworms hairworms are not macroscopically visible in the droppings but can only be diagnosed by microscopic examination of these droppings. The hairworm is contrary to the roundworm not animal specific and can be transmitted by chickens, turkeys, quail and pigeons. Even a small number of these worms can have a major negative effect on the condition of the racing pigeon. Very rarely we can also see a pigeon with a tapeworm infection (Hymenolepis columbae). In that case only one pigeon is infected and direct infection of the other pigeons is not possible.
The affections is being transmitted by uptake of mature worm eggs excreted in droppings of the infected pigeons or birds. In case of a tapeworm infection there is always the presence of an infected intermediate host, e.g. a little slug. Only after the intake of this infected intermediate host the pigeon itself will be infected.