By Dr Steve Surujbally
I suppose all worms are, in one way or another, pernicious. But the wretchedness of the hookworms has no equal in the helminth world. It is as if every aspect of this worm is geared for aggression and survival. The hookworm is the undisputed king of wormdom, notwithstanding its size which is about ¼ inch to ½ inch long (sorry Flavio – ½ to 1 cm in length). Let me share with you some features of this worm’s malevolence.
These wretches are voracious blood-suckers, and in order to ensure that their blood-sucking ability is not compromised, they secrete anticoagulins so as to prevent the host’s blood from clotting at the point on the intestinal wall injured by their teeth (usually, they attach themselves to the walls of the small intestine and draw blood).
As if that were not bad enough, the hookworm larvae (immature stages) can actually penetrate the dog’s skin from the outside. It is quite an amazing biological feat for them to get through the relatively hard hide of the dog.
Well, again, nature has endowed this monster’s larvae with the ability to secrete a substance which softens and disintegrates the outer layers of the dog’s skin. In fact, these larvae are so aggressive that they can penetrate the hard paws of a dog’s feet.
When the hookworms are not boring through the skin, they present themselves to be ingested (contact with contaminated soil and/or faeces, usually). These larvae grow and mature in the intestine to become adults which lay eggs that are deposited in the excreted stool.
It is also important to remember that, as with roundworms, a hookworm infection can take place even when the pup is still in its mother’s womb.
In animals older than three months, the larvae tend to do a body passage and migrate through the lung where physical damage is caused, and which may result in a secondary bacterial invasion into the lesioned lungs.
During this wanderlust, the larvae later find themselves in the muscular tissue. They stay there until they are activated by some stress, for example malnutrition and pregnancy. Very often, they accumulate in the mammary glands, thus making it easy for the young pup to become infested as it suckles at the infected breasts.
Symptoms
It was mentioned that the hookworms are primarily blood-suckers. In addition, the process of blood-sucking creates bleeding ulcerations in the intestines. Obviously, because of the raw lesions in the gut, bacteria can then secondarily invade the wounded entrails.
Consequent on the points raised above, it is clear that symptoms associated with a hookworm infestation are those that involve haemorrhage and blood loss, and can result in a full-scale anaemia.
The anaemia results directly from the loss of blood due to the actual blood-sucking by the hookworms or their immature stages, and from the bleeding ulcers. It has been calculated that ten worms can suck up to one millilitre (1 ml) of blood in a 24-hour period. Can you imagine what the blood loss will be like in the space of a week when, say, one hundred worms are
voraciously feeding? Now imagine that activity in a two-pound puppy.
A bloody diarrhoea is another cardinal symptom associated with a hookworm infection. The stool is characteristically dark red to tarry black in colour.
I should mention, in passing, that there is serum seepage around the area where the worm is attached to the intestine. This in turn, could reduce the blood protein level by as much as 10 per cent.
Now, with all that blood and protein loss, one will expect the young puppy to be unthrifty, debilitated, listless, losing weight/emaciated, iron deficient, dehydrated and vomiting.
Some puppies survive the onslaught of the hookworm. They might even develop a tolerance (partial immunity?) for the hookworm. But even these survivors don’t fare well in the long run.
They continue to show signs of malnourishment, and suffer from a chronic anaemia. These survivors always seem fragile during their youth and are often susceptible to even the slightest pressure from bacterial and other agents later in life.
Adult dogs do get (rather rarely) hookworm infections and when they do, the symptoms are diarrhoea, progressive weight loss, and anaemia. Mature, well-nourished dogs may habour hookworms without showing any signs of an infestation. However, they represent a direct and indirect source of hookworm infection for pups and young dogs.
We had documented earlier that the hookworm larvae can actually penetrate the skin and migrate, via the bloodstream, to the lungs (coughed up, swallowed, enter the intestine and become adults). During this lung passage, physical damage is done to the lung tissues.
Consequently, a pneumonia could develop in puppies less than 3 months of age.
Lastly, the literature speaks of a dermatitis which is associated with hookworm infection. This dermatitis seems to be confined to the interdigital (between the toes) spaces.
Next week we’ll look at the treatment and control of the hookworm.
