Over the past few weeks we have been discussing intestinal worms in some detail. However, there is another worm that infects dogs and, occasionally, cats. I am referring to the heartworm which, as the name suggests, lives in the heart of the dog (cat) – primarily in the right heart chambers and in the pulmonary artery (and sometimes also in other big blood vessels). This is also one wicked worm, especially because of the insidious nature of the development of the ailment it causes. By the time the symptoms show themselves, the dog has been debilitated even to the point of no return.
If the dog dies after a lingering and excruciating sickness one can find, via a post mortem examination, a bundle of worms like spaghetti in the right heart chambers.
This disease is raising its ugly head in Guyana in proportions that are disturbing. There are certain areas in this country that one can legitimately designate as heartworm enclaves. The Lower East Coast is such an area. The extent of canine heartworm infection could actually be much greater, but we are not researching this disease with any great focus. If one or two of the veterinary fraternity or the Animal Services Division of the Ministry of Agriculture acquire special detection kits and would like to embark on an investigation of a larger scale, we will then know how widespread this malady truly is.
I should mention that canine heartworm is to be found all over the world, especially in areas at (and below) sea level in the tropics and subtropics, wherever the mosquito can be found. The mosquito transmits canine heartworm!
The prevention and treatment of canine heartworm cannot really be attempted unless one understands the life cycle of the worm.
Heartworm life cycle
The tiny (can’t be seen without the aid of a microscope) immature stage (microfilaria) of the heartworm, which is in the mosquito’s mouth parts, is deposited by the mosquito on the skin. These active microfilariae penetrate the skin. The immature stages of the worm begin to grow (for almost two months) before heading for the heart. Once they have arrived in their new home (the right side heart chambers) they begin to mature and become sexually active. Then they begin to give birth to new microfilariae, which your veterinarian can discover by examining a blood sample. We are told that one female heartworm can give birth to as many as 5,000 microfilariae in one day. The veterinarian can pick up dozens in one drop of blood.
The whole cycle – development in the mosquito, growth in the host’s tissues, circulation in the dog’s blood, further development in the heart chambers – can take up to six (6) months. In the tropics, this cycle could be shorter (4-5 months) than in temperate and sub-tropical climates.
Of course, once undetected, the adult worms (once they are males and females) can continue to produce the microfilariae. The worms can live in the heart for years before even the well-cared-for dog succumbs.
During one post mortem (on a dog that was not a patient of mine, let me hasten to add), I found over one hundred worms in the heart. Some of the worms measured about six inches in length. The literature tells us that the females are larger than the males, can reach lengths of one foot and can number as many as 250 with mature females discharging thousands of young microfilariae into the bloodstream daily!
As you can see, the dog with a heartworm infestation is in big trouble. Once the contraction function of the heart is compromised by the presence of a huge ball of worms, then the
other organ systems (liver, kidneys, lungs, etc) begin to fail.
Next week we’ll deal with the symptoms and perhaps with treatment and prevention.
Please implement disease preventative measures (vaccinations, routine dewormings, monthly anti-heartworm medication, etc) and adopt-a-pet from the GSPCA’s Animal Clinic and Shelter at Robb Street and Orange Walk, if you have the wherewithal to care well for the animals. Do not stray your unwanted pets, take them to the GSPCA Clinic and Shelter instead. If you see anyone being cruel to an animal, get in touch with the Clinic and Shelter by calling 226-4237.
