While dogs and cats can become ill with an infectious disease in the winter time, it is more common to see infectious disease emerge during the warmer months, especially late summer. There are a few reasons for this:
1) many infectious diseases are transmitted from animal to animal and require at least some sort of contact between individuals for transmission. Dogs playing in large groups in the summer are a good example: if one dog has kennel cough (or infectious tracheobronchitis), it is easy to see how the others may catch it.
2) many veterinary (and human) infectious diseases are transmitted by critters such as fleas, ticks, and mosquitos, whose populations increase in the summer. Fleas carry the larval stage of tapeworms. If your cat (or dog) is a mouser, she will likely ingest fleas on the mouse and can acquire a tapeworm infection. Fleas also carry other microorganisms that can cause nasty disease in our pets. Many of these are transmitted to the pet's blood cells (similar to malaria, which is transmitted by mosquitos). Ehrlichiosis, Lyme disease, and Rocky Mountain Spotted Fever are diseases that are transmitted by ticks. Dogs and people can be affected. George Bush is currently being treated for Lyme disease!
Not only do these critters transmit infectious disease, but their presence alone can be a nuisance at best, and even life-threatening. Fleas are little vampires, so a severe infestation on a kitten or even an adult cat can result in extreme blood loss (anemia) that can result in death. Fortunately, most pet owners are astute enough to run to the vet when they see a single flea. Fleas cause itchy skin due their presence, their bites, and even an allergy to the flea's saliva. This allergy, or flea allergy dermatitis, can cause great distress in both cats and dogs. Treatment is aimed at killing the fleas and using potent antihistamines for the allergy.
Most ticks found in Ontario, while despicably gross-looking, are in fact NOT carriers of dangerous diseases, including Lyme. It is not uncommon for a veterinarian to remove a tick from a pet and send it to a laboratory in order to identify it (public health can even run a PCR, a very sensitive test, to see if the tick is carrying disease! Having said this, Lyme disease has been on the increase in Ontario (especially in humans), which likely reflects the increase in education of physicians in diagnosing the disease.
Mosquitos are carriers of heartworm disease, a potentially deadly disease in dogs and even cats south of the border. While heartworm disease is uncommon in Ontario, its incidence is certainly not zero. Monthly heartworm preventives should be given to those dogs at risk, all summer long. Many clients ask me, "Well if the incidence is low why should I give heartworm medication?" This is an excellent question. There are two good reasons why I recommend it to most dogs: 1) while the incidence is low, morbidity and mortality are much higher, which means that dogs affected with heartworm disease can get quite sick and even die, especially if the number of worms is high. Vets would rather prevent the disease than treat it. 2) Very importantly, many, if not most, of the heartworm preventives on the market today are broad-spectrum, which means they cover much more than just heartworm disease. They can kill and prevent fleas and ticks, and of utmost importance to me, they can kill and prevent many types of intestinal parasites which are MUCH commoner than heartworm disease.
I must remind all readers that the administration of vaccines and preventive medication must be tailored to the specific needs of individual pets. An indoor cat that lounges in front of a window all day long would likely not be a candidate for monthly flea prevention. A dog that lives in its owner's purse (I do not condone this!) should not be vaccinated for leptospirosis. I encourage all pet owners to ask their vets many questions.
These vaccines and medications exist for a reason. If your vet feels that your pet is a candidate for a certain vaccine or medication, then he or she is likely right.
