First Street Veterinary Hospital Newsletter - March 2008

Got Fleas?

Ahhh…Spring! The grass is turning green, the daffodils are blooming, and the days are getting longer and brighter. What a wonderful season in the Pacific Northwest. But with better weather comes something else…FLEAS (and other parasites).

This month’s newsletter is going to focus on several different parasites our furry friends can harbor and how easy it is to prevent them. And prevent them we should: not only can they cause illness to our 4 legged friends but many of them are zoonotic (that means they can spread to people to cause illness also). The good news is there are many safe and effective medications available to prevent all the common internal and external parasites we see in this area.

Let’s start with worms…I know it’s a gross subject but the CDC estimates that 30-50% of domestic pets carry gastrointestinal parasites (worms). Even well cared for pets can have worms and I’ll explain the life cycles that allow this. Young animals are more at risk.

Roundworms are the most common worm in the NW. There are 3 types of roundworms but they all have similar lifestyles. Step one is when a worm egg is passed in the feces of an infected animal, the embryonic worm develops in the egg in the environment for a month, and then the egg is infective. Roundworm eggs can remain infective in the environment for months to years. Step two is when the egg is picked up orally by another animal and proceeds to the intestinal tract to be hatched, then it burrows out of the intestinal tract to encyst in the host’s other body tissues. If the new host is a dog or cat the life cycle proceeds; if the new host is another animal, such as a rodent, the larvae wait encysted until eaten by a cat or dog. During step three the larvae can remain encysted for years. If the host is a dog or cat, the larvae waste no time, but continue the migration to the lungs and develop into third stage larvae, where they burrow into small airways and move upwards to the throat where they are swallowed and enter the intestines for the second time. Once back in the intestines the larvae complete maturation and begin to mate. The first eggs are laid about one week after the larvae have arrived in the intestine the second time and 4-5 weeks after the infection first appeared.

Woo…did you catch all that? The important part is this: when pets are dewormed, this affects only the worms in the intestinal tract. It does not affect encysted larvae or the larvae on migration throughout the body. This is why it is very hard to completely get rid of worms, and also why a negative fecal test does not rule out being infected with worms. A fecal test is only testing for the presence of eggs in the feces. As you can see there are no eggs in the feces until 4-5 weeks after the first infection. And if the pet is dewormed at 4 weeks, in another 3 weeks the encysted larvae could now be producing eggs—this is why we recommend monthly deworming protocols. (See below for recommendations.)

Roundworms are the main cause of a serious condition called visceral larva migrans in humans. Most victims are children. They are inadvertently infected by consuming eggs (typically by getting dirty fingers in their mouths). The worm is not present in the correct host but tries to complete its life cycle anyway. The worm gets lost in the human body (often in the eye), dies, and generates an extreme inflammatory reaction. If the worm dies in the eye, blindness usually results. (More on preventing this later)

There are two other more uncommon worms found in the Pacific Northwest. These are hookworms and whipworms (no whipworms in cats). Hookworms live in the small intestine and live on blood; therefore severe anemia can result in our pets. Contaminated soil can be a source for human infection through the skin for cutaneous larval migrans. Humans can also be infected by eating improperly washed vegetables. Whipworms live in the large intestine and can cause severe diarrhea. Female whipworms only periodically lay eggs so diagnosing whipworm infection can be very difficult. Soil contaminated by whipworms remains so for many years. It is virtually impossible to remove the eggs from the soil or kill them. The good news, however, is this is one intestinal parasite that is not readily transmissible to humans.

Now let’s talk about tapeworms. There are 2 main types of tapeworms in our area but the predominant one involves the flea. The life cycle is complicated but involves flea larvae feeding on tapeworm eggs and the eggs hatching in the flea intestine, then the flea is swallowed by our pet during grooming and the tapeworm larvae matures in the pet’s intestine. The tapeworm really doesn’t cause much damage to the pet, but as it matures it breaks off segments and these are shed in the stool and contain more tapeworm eggs. We often see these on fresh stool as small white pieces resembling rice (and moving if very fresh) or deposited around the anus and looking like sesame seeds. Theoretically people can be infected as well but only by ingesting a flea. The tapeworm eggs themselves are not infective to humans or pets (just fleas). Seeing evidence of tapeworms indicates there is an ongoing flea issue, although it does take only a few fleas ingested to become infected. If you see tapeworms, look closely for fleas! Tapeworms should be treated any time they are seen.

Next onto fleas…fleas earn their living by sucking blood. The adult flea leaves behind partially digested blood (“flea dirt”), which is a food source for the larvae that hatch from the eggs. Infestation can lead to anemia in some animals. Other animals can develop severe allergies to fleas. Even if live fleas are not seen, the presence of flea dirt confirms there are live fleas in the environment. Also only animals allergic to flea bites will generally itch. This means that the animal that is not allergic will not be scratching or losing fur, thus you may not realize there is an active infestation. Adult fleas make up only 5% of the overall flea population and are the easiest form to kill. Eggs can be rendered non-viable by drying them and larvae are somewhat easy to kill. However there is currently no product available that is very effective at killing the pupae stage. And fleas can remain in this stage for months!!

One parasite I haven’t mentioned is heartworms. This is because we don’t have a major problem (yet) with heartworms in the Northwest. However there are always a few cases each year in Oregon (especially in south Willamette Valley) and many of our neighboring states have them. These are worms that live in the heart and lungs and are spread via mosquitoes. Because of where the worms live they can cause significant damage and death to our pets. They are not infective to humans. As you will see below most of our recommended monthly deworming protocols prevent heartworms as well so this is an added benefit for our Northwest pets.

Now how do we manage all these nasty creatures? Fortunately in the past few years we have many products available that are both safe and effective. I’ll outline some of these (see table on page 3) but we always try to tailor a parasite prevention program based on the pet, family, and activity level. The products mentioned in the table carry a guarantee against internal parasites if purchased from a licensed veterinarian. This guarantee is voided if the products are purchased from an unauthorized source.

One other note of caution—there are many OTC products that claim to be just as effective at flea control as the prescription products. READ THE LABEL!! Some of these products are only for dogs and can be deadly to cats, even to cats in the same house as treated dogs. The packaging may be similar but the chemicals used are very different.

One other thing I want to talk about is not really a parasite but it has been weighing on my mind for a while. This is a disease that is still fairly rare in our area and the previous vaccinations tended to have many problems. However it is becoming more prevalent and the newer vaccines are more effective and less problematic. Leptospira is a bacterium that can cause leptospirosis, a disease that can cause a potentially fatal illness. Even more disturbing is the fact that you could contract the illness yourself by coming into contact with the urine of an infected dog. There are many different serovars (or strains) of Leptospira. Carriers include skunks, raccoons, squirrels and other rodents. Their urine contaminates ponds, streams and puddles as well as vegetation and soil. The organism can survive up to 180 days in wet soil and even longer in stagnant water. The bacteria can invade through the skin or mucous membranes when your dogs checks out the area.

Symptoms of the acute form include fever, vomiting, diarrhea, anorexia and increase in thirst and urination. The bacteria attack the liver and kidney and can cause permanent damage. Prognosis for survival is guarded even with treatment. However, most infections are of the chronic type. These dogs don’t show signs of illness but they can shed Leptospira bacteria in their urine for months to years. Vaccines have recently become available that protect against 4 different serovars. Unfortunately vaccinating against one serovar does not protect the dog from any of the others. Please contact us if your dog likes to explore ponds, streams, puddles or other wet areas as we may now recommend vaccinating against this disease.

• For Dogs:

Sentinel (milbemycin oxime and lufenuron)—once monthly chewable tablet that prevents heartworms, roundworms, whipworms, and hookworms. It also contains a flea growth regulator that prevents the eggs from hatching, essentially sterilizing the flea.

Or,

Interceptor (milbemycin oxime)—once monthly chewable tablet that prevents heartworms, roundworms, whipworms, and hookworms. It does not prevent flea infestations.

And

Comfortis (spinosad)—once monthly chewable tablet that kills adult fleas very quickly (100% within 4 hours) and continues to kill fleas for 30 days. We recommend using this product as needed for most animals or monthly for flea allergic dogs or dogs that are more prone to picking up fleas (such as dogs at day care).

By utilizing the above protocol all major parasites can be prevented, we avoid pesticide residue on our pets, and we help to protect the environment against parasite infection.

• For Cats:

Program (lufenuron)—injection given every 6 months that prevents flea eggs from hatching, essentially sterilizing the flea.

And:

Revolution (selamectin)—once monthly topical treatment that kills fleas, prevents heartworm, prevents and treats roundworms and hookworms, prevents and treats ear mites.

We recommend both the above for all cats that go outdoors and for indoor only cats if there are any children or immunocompromised adults in the household, or for any flea allergic cats.

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Other ways to prevent parasites include:

• Scoop the yard daily where dogs defecate.
• Have a fecal test done on each animal at least yearly and preferably twice yearly.
• Teach children to wash their hands before eating.
• Wear gloves while gardening and wash vegetables well before eating.
• Keep sandboxes covered when not in use.
• Wear shoes outdoors whenever possible.