Over the last six weeks, the PET CARE column has been discussing all the salient aspects of worm burdens in dogs (and cats). I can tell you, dear readers, that never have we received so many calls on this theme. And quite rightly so. Gastro-intestinal worm infections do indeed seriously impact on the health of both young and adult companion animals. I shall therefore continue the discussion on worm infestation and respond intermittently to queries made.
The most frequent enquiry thus far was/is:
CAN HUMANS CONTRACT WORMS FROM THEIR PETS?
The answer is yes. Worms infecting dogs (to a lesser degree cats) can in fact assume residence in humans. Then, of course, it becomes a human medical problem. Caregivers are advised to discuss the matter with their physicians for prevention, detection and treatment accordingly.
HEARTWORM DISEASE IN COMPANION ANIMALS
I had decided to deal with the Heartworm infestation when the discussions would center on heart problems. However, since we were dealing extensively with worms (albeit those that infect the Gastro-Intestinal Tract), it may be more appropriate to include Heartworm infestation at this stage.
Let us begin:
Heartworm Disease (HD) is a potentially fatal, but preventable, infection caused by worm parasites, similar to the causative agent for Elephantiasis (aka “Big Foot” in local parlance) and Filariasis (in humans). Mosquitoes transmit these worms, especially in areas where temperatures are above 80 ℉ (27 ℃), and where humidity levels are high (over 80%).
As the name suggests, this worm lives in the hearts of dogs (and cats), primarily in the right heart chambers and in the pulmonary artery (and sometimes also in other large blood vessels). This is 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 seriously weakened.
If the dog dies after a lingering and excruciating sickness (due to heart function first being compromised and progressive shutting downs of all the other organ), one can find – usually via a postmortem examination – a bundle of worms like spaghetti in the right heart chambers and in the large blood vessels that enter and leave the heart chambers.
The prevalence of this disease is increasing in Guyana in proportions that are disturbing, especially in areas where preventative medication is not available or in animals which do not receive regular monthly medication. There are certain areas in this country that one can designate heartworm enclaves. The Lower East Coast of demerara is one such area. The extent of canine heartworm infection is, in all probability quite huge (pan-Guyana?), but we are not researching this disease in any great detail. A large-scale investigation is needed so that we will gain a better understanding as to how widespread this malady truly is. I understand that at least one commercial laboratory has the wherewithal to accurately check for heartworm. Of course, any veterinarian with a microscope can also determine – with a fair degree of accuracy – the presence of heartworm larvae in a fresh blood sample
I should mention that canine heartworm is to be found all over the world, especially in areas at sea level (and below) in the tropics and sub-tropics, wherever the mosquito can be found. The mosquito transmits canine heartworm!
HEARTWORM LIFE CYCLE
The prevention and treatment of canine heartworm cannot really be attempted unless one understands the life cycle of the worm.
The tiny (not visible without the aid of a microscope) immature stage (microfilariae) of the heartworm, which is in the mosquito’s mouth parts, is deposited by the mosquito on the skin. These robust microfilariae then actively penetrate the skin. These immature stages of the worm begin to grow (for almost two months) before heading for the heart. Once they 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. It is documented that one female heartworm can give birth to as many as 5,000 microfilariae in one day. The veterinarian can pick up hundreds in one drop of blood.
The whole cycle – development in the mosquito, growth within the host’s tissues, circulation in the dog’s blood, further development in the heart chambers – is roughly around six months. In the tropics, this cycle could be shorter (4-5 months) than in temperate and sub-tropical climates.
Of course, once undetected, and untreated, the adult worms (as long as there are males and females in the heart) can continue to produce the microfilariae. The worms can live in the heart for years before even the well-cared for dog succumbs. During postmortem examinations, hundreds of adult worms are found in the heart (see photo). Worms generally measure about six inches in length. The literature tells us that the females are larger than the males and can reach lengths of 12 inches and number as many as 250, with the mature females discharging thousands of young microfilariae into the bloodstream daily!
Dog’s Heart
infested with Heartworms
As you can see, the dog with the heartworm infestation is in big trouble.
Next week we shall describe the symptoms of canine heartworm disease.
