Summer, Worms and Heartworm

Summer is back again already and one day soon (oh please, very soon) it’s going to rain again. We love the rain – suddenly everything around town that spends most of the year looking brown springs back to green overnight. But it’s not only our tropical plants and grasses that love the rain. Rain and summer warmth are also the perfect conditions for some of our more troublesome parasites to flourish. We’ve already seen the ticks and fleas getting into top gear this year, and we’re heading very quickly into the best time of year for hookworms and heartworms both.

We’re always at you to stick with heartworm prevention and make sure your cats and dogs are covered for intestinal worms too – but we don’t always have the time to explain the whole story, particularly about just how it is that our pets come into contact with these things to start with.

So here’s a brief rundown on the two main ones that can actually kill your pets if left uncontrolled.


Unlike all the other worms that cause our animals problems, heartworms are blood borne. Heartworms live in the heart (obviously) and not in the intestines like all the rest do. So how do they get from one dog to another dog? The answer is – the mosquito!

When a mosquito bites an infected dog, if that dog is not on heartworm prevention and does have heartworms in its heart, the mosquito picks up a dose of the very, very tiny early larval heartworm stages that circulate in the dog’s blood stream. These larvae then undergo a bit more development within the mosquito itself – the mosquito incubates them for about 2 weeks.

Finally, while the mosquito travels about gathering more blood meals from all the neighbourhood dogs, it leaves in every one of these donors a little injection of the hitch-hiking heartworm. These worms are then carried through the circulation and settle in the heart and the main blood vessels to the lungs – and here’s where they cause all the trouble. So now the link is very obvious – summer and rain equals mosquitoes, and mosquitoes equals heartworm disease.

The picture tells the story… Don’t be there!!! If in doubt, come in to the clinic and have us check it out for you before it is too late.


These are the nastiest of all our intestinal worms. While all worms cause trouble, hookworms cause lots of trouble very quickly. Young animals are particularly susceptible to infection and the effects of this intestinal parasite. Infected dogs pass eggs in their faeces. These eggs are not immediately infective to other cats and dogs and people. They have to undergo a few phases of development on the ground before they are capable of continuing their lifecycle in the animal.

During their developmental phase on the ground hookworm larvae are susceptible to the effects of the weather – if it’s really hot and dry, they may die from dessication, or they may not reach an infective point before they can no longer survive the big world. However, in a rainy summer many more worms survive on the ground and go on to infect more animals. More infected animals means more eggs. More eggs means more infections.

Hookworms not only feed on blood by attaching to the lining of the intestine, but they also produce an anticoagulant (a substance that prevents clotting). So every time they move from one spot to another, they leave a bleeding wound behind – check the teeth in the photo – the blood loss can be catastrophic and even fatal.

Never forget that dog and cat parasites can infect people as well. This very serious business will not occur if everybody’s pets are properly cared for with correct and effective preventatives.

So that’s how the weather influences what goes on in and around our pets. It’s amazing how many little ecosystems exist in the world and how well adapted some parasites are. If you’re sticking to a good worming routine and have your dogs and cats covered by routine heartworm prevention, then none of this should cause you any alarm. If you are worried that you may be overlooking some aspect of parasite cover, please call us and we’re more than happy to work through a prevention schedule that’s easy and convenient for you and your furry family.