Roundworms
Roundworms (Toxocara) are very common. It has been speculated
that 85% of puppies are infected with roundworms. Toxocara canis
(TC) and Toxocara
leonina (TL) are the two roundworms of the dog, with the former being far
more prominent. Both worms are large, around 3 inches. Both are diagnosed
by standard microscopic fecal exams. False negatives occur when no eggs
have been shed into the sample presented. Infection occurs in both TC and
TL by ingestion of eggs when contaminated feces are shed into the
environment. However, the vast majority of TC infection occurs by
transplacental migration from the bitch to the pup. Immature larvae from
either method of transmission of TC undergo migration from the gut into
various tissues. The majority of the larvae migrate through the liver,
diaphragm, lungs and up the major airways. As they move up the trachea,
occasionally several worms will be coughed up by the pup and discovered
in the expectorant. Most of TC will continue their migration and be
swallowed, moving down the esophagus, into the stomach and back into the
small intestine where they reach adult status and begin shedding eggs.
Some of the migrating larvae become encysted in tissues as migration
occurs.
Infection by TL does not produce this larval migration. Most dogs develop
some immunity to reinfection of TC and TL. Adult
infection is estimated to be around 10-15% in the US. Encysted
larvae return to the intestine when severe stress
occurs to the host.
Signs of roundworms can be serious in puppies producing abdominal pain,
bloating, dull coat , diarrhea and occasionally fatal small bowel
obstruction. Migration can cause respiratory signs that mimic upper
respiratory infections. Occasionally, serious pneumonia result. |