Heartworm 101 - Life and Times of a Freeloading Parasite

I have a tendency to be long-winded, so I'm going to simplify this for the impatient folks out there because the message is very important. Heartworm disease kills dogs and cats. Treatment is risky and expensive. Heartworm is (fortunately) easily preventable. Therefore, all dogs and cats should be on year-round monthly preventatives.

It really is that simple. However, if you want more than just my word on that - if you want to know what heartworms are, how infection and disease occurs, and why giving those preventatives monthly is so important - keep reading.

What Are Heartworms?
Heartworm is the common name for Dirofilaria immitis, a large roundworm parasite very similar to those disgusting white intestinal worms that dogs and cats become infected with from time to time. While the commonness of infection varies from place to place, heartworm has been diagnosed in all 48 continental states and many other countries as well. Their life cycle is rather complicated, but a basic understanding goes a long way toward both understanding the disease and making sense of veterinary recommendations about preventatives.

Microscope view of heartworm larvae
in a dog's blood.

Dogs are the natural host for adult worms, which infect the large arteries of the lung, and in heavy infections are found in the heart itself. Males and females mate to produce larvae called microfilaria (i.e., small threadworms). These microscopic worms live in the bloodstream for up to two years, waiting to be sucked up by another disgusting little critter - mosquitos. This triggers the larvae to mature through a couple more stages, eventually winding up back in the salivary gland of the mosquito - just in time to get injected back into another unsuspecting dog. Over the next six months, those microscopic larvae will travel to the vessels of the lungs and mature into adult worms that may be nearly a foot long, ready to mate and start the cycle all over again.

How Do Heartworms Harm Pets?
It doesn't take a medical degree to realize that bunch of worms clogging up the bloodstream is unhealthy. Indeed, when many worms are present they interfere with bloodflow into the lungs and force the heart to work harder, leading to classic signs such as exercise intolerance and coughing. The severity of such problems are largely a function of how many worms are present - pets with three or four worms may show no overt signs, while those with dozens will likely be in rough shape.

Heartworms inside a dissected heart.

Simple mechanical blockage of the heart and vessels is far from the only problem, however. For starters, the immune system is really, really not a fan of freeloading parasites. Significant inflammation can result in the lungs from both adult and juvenile worms; indeed, research is pointing toward juvenile worms as being a major cause of feline asthma syndromes.  In response to the worms, the immune system produces massive amounts of  antibodies - proteins directed at identifying and helping destroy invading microorganisms. Unfortunately, for all its bluster the immune system is pretty impotent to deal with the worms, and winds up doing much more harm than good. The arteries the worms live in thicken from inflammation, and all those antibodies wind up settling out in small vessels - particularly in the kidneys, where they may cause a fair bit of damage.

One of the most dangerous complications of heartworm disease happens when the worms die. Dead adults get pushed downstream until they lodge in smaller vessels of the lungs, forming an embolus that cuts off blood to that part of the lungs until the body can break it down. Enough of those dead worms in the wrong place can be fatal. Furthermore, once adults set up shop in the cadiovascular system they begin pumping those tiny microfilaria into the bloodstream - potentially millions of them. Strangely, these don't seem to cause much trouble while alive; however, they turn the pet into a walking infection source for every mosquito in the area, which in turn may infect other pets. When the larvae die, though, the dead parasites trigger the immune system and cause microscopic abscesses where they land. This probably isn't a big deal when most of them are alive, but it is a major concern when treating pets with the disease, as millions dying at once can potentially send an animal into anaphylactic shock. Both of these are primary reason why infected animals need to be under strict exercise restriction, and why treatment must be undertaken with close monitoring at the hospital.

So, that's what heartworms are and what they do. In the next article, we'll talk about preventatives - what options are out there, why giving them every month is important, and about the benefits they provide aside from heartworm protection. We'll also talk about screening tests, particularly why we recommend yearly testing for all pets - even those on preventatives.

Click here for Part II - Prevention and Testing.

Bad kitty! Or…sad kitty?

Litter box problems, or “inappropriate elimination behaviors," are among the most common complaints I hear from cat owners.  If it has ever happened in your home, you're probably thinking “inappropriate” is a rather mild way to describe urine or feces in the middle of your carpet, but bear with me.  With some investigative work and patience, we can help most cats get over bad bathroom behavior. And, with the right information you may prevent future problems.

Medical causes

The first step in these situations should always be a visit to your vet to rule out underlying medical causes.  Conditions like kidney disease, diabetes, and hyperthyroidism can increase urine production, while urinary tract infections and bladder stones are uncomfortable and may result in frequent urination.  Likewise, issues such as parasites, constipation, and inflammatory bowel disease may make defecation urgent or uncomfortable.  Even arthritis can affect bathroom habits – imagine if you had to climb over a waist-high wall to get to the toilet!  So, it’s possible your feline friend doesn’t feel well and just can’t make it to the litter box.  A thorough physical exam, blood work, urine analysis and/or fecal exam will establish your cat’s general health status and help guide treatment if necessary.

Unacceptable, Human!

Behavior

Now that we’ve ruled out medical conditions, it is safe to start questioning behavioral causes… But before you send kitty to a psychiatrist to work out his anger issues, we need to talk about YOUR behavior too.  You may think that your cat doesn’t deign to notice you unless it’s dinner time, but cats are actually quite sensitive critters.  They can’t tell you with words that they are stressed out by something in the house, but peeing outside the litter box is one way to get your attention (my two cats prefer to barf in my shoes or self-mutilate, respectively).  Here are some things that might be ruffling kitty’s tail feathers.

Litter box issues:

• Hygiene – Is it possible that you and kitty have different standards when it comes to cleaning the bathroom, so he decided to seek out a cleaner facility?  Most cats are quite fastidious, so litter should be scooped daily and changed out completely on occasion (non-clumping litter should be dumped every few days). You might also consider tossing your box for a new one if it’s really worn, as plastic can retain urine smells.
• Availability – Are there enough litter boxes in the house?  I recommend having one box per cat plus an extra (e.g. 3 cats, 4 boxes) unless you have a very large number of cats, and then you will probably get into trouble despite the number of boxes.  There is a scientific study from the 80s showing that individuals with 10 or more cats have a 100% probability of becoming a victim of inappropriate urination, and a 90% probability of eventually being a crazy cat person (ok, maybe only the first half was shown in the study).
• Location – Maybe kitty was just settling down in his laundry room litter box to “read the Sunday paper” when that really loud timer on the dryer buzzed and startled him into Tuesday.  If you think location could be the problem, leave the current box in place but add one somewhere else in the house.
• Type of litter – Cats have preferences about their potties, and it may be your cat doesn't care for that fresh pine scent as much as you do.  Try a few different types (clumping, clay, recycled newspaper, etc.) at the same time to give kitty a choice of textures and smells.  Be sure to include a finely-textured clumping litter in your test, as it was chosen more than twice as often as other types in a thorough study by behaviorist Dr. Peter Borchelt.
• Type of box – Try out a new box shape or size.  However, a word of caution on covered boxes…  Many people favor covered litter boxes for obvious reasons, but I find most cats do not, especially in multi-cat households. For example, my cat thought his sister was playing hide-and-seek in the covered box we used to have, so he would wait outside and ambush her upon exit.  Needless to say, she did not enjoy this.

Environmental stressors – Pretty much any event or change in your cat’s life can fall into this category, but common issues include:

• New people – Houseguests, new spouse or roommate, new baby, etc.
• Disruption of environment – Moving, renovations, holiday decorations and celebrations
• Change in your schedule – New job, leaving for vacation
• Visiting the vet – I wish they all loved seeing me…
• Inter-cat aggression – self explanatory, and common.
• New pets – Introducing a furry family member can be a very delicate process, and strategy may depend on the personalities of your current critters. I recommend talking to your veterinarian if you are thinking of adding a pet.

These issues are tricky, as it’s often difficult to control them unless you plan on letting your cat completely run your life.  What you can do is implement some practices that will hopefully make kitty more resilient to life’s little blips. We've already discussed litter box recommendations, but additionally all cats should have fresh food and water, something they’re allowed to scratch, and a safe space where they can go to get away from other pets and people if they choose.  Perches can often provide such a space, and when placed near a window also serve as a source of entertainment.  You should also carve out some time each day to interact with your cat via play, grooming, or even training (yes, cats can be trained!).  Toys and catnip are great stimulation for some kitties, while others will be engrossed by “cat TV” or nature videos.  Feliway (http://www.feliway.com/us), a synthetic pheromone product, may also help reduce stress.  Be creative and try different things to find what lights your cat’s fire, but the message is that your cat may be bored or stressed if his basic needs are not met, and this can lead to health and behavior problems.  Ohio State University's Indoor Pet Initiative (http://indoorpet.osu.edu/cats/) has done a lot to further our understanding of how environmental enrichment can help our feline friends live happy lives.

No dice, Doc.  Now what?

So you’ve had kitty vetted, offered a Pu-Pu platter of litters and boxes, enriched his life and pheromoned the heck out him, and he’s still “thinking” outside the box.  Now may be the time to head back to your veterinarian, or a veterinary behaviorist if one is available and finances permit.  If the problem has been going on for a long time or your cat is particularly sensitive to environmental stressors, finding a solution can be very specific to the individual animal and situation.  There are anti-anxiety medications that can help, especially in cases where feline housemates are not getting along, but they are not magic pills and must be used in conjunction with environmental modifications, many of which have been discussed above.

To sum up…

• Rule out medical causes
• CLEAN the litter box
• Try different types of litter in different boxes in different locations
•  Reduce stress with environmental enrichment and interaction with your cat
• Medications can be useful in conjunction with behavior and environment modifications

-Dr. Courtney Smock

The Truth About...Cataracts

At least a couple times a week someone brings in an older dog and tells me the pet is getting cataracts. Fortunately, the changes they've noticed usually aren't true cataracts and don't significantly trouble their vision. True cataracts do happen in pets, though, and not uncommonly either. When cataracts are large or progressive they can lead to blindness or even painful glaucoma, so it's important they are recognized and closely monitored by your veterinarian.

The lens is #11; the pupil is #7.

Cataracts are imperfections in the lens - the clear disk which sits in the pupil and focuses light on the back of the eye, which in turn translates that light into an image*. So, the important thing about the lens is that it is clear and flexible (little muscles attach that deform it to focus the light so you can see near and far). There is a very intricate, highly organized structure to the proteins in the lens that allows this to happen. A cataract, then, occurs when this structure breaks down, turning part or all of the lens opaque. Light can no longer pass through that area, interfering with vision to a degree dependent on the size of the cataract. A small cataract may have no significant impact on vision, but complete (or mature) cataract essentially means that eye is blind.

Nuclear sclerosis. Note how the opacity is central
and surrounded by a halo of normally transparent lens.

Before we go any further, let's clarify what most owners get concerned about, a phenomenon called nuclear sclerosis - which thankfully doesn't have a noticeable effect on vision and isn't a true cataract. As dogs age, new lens fibers slowly develop from the outside edge and move inward, slowly compressing the center (nucleus) of the lens. The increased density results in a hazy appearance that is often confused with a cataract, but unlike a cataract light still passes through fairly normally. Indeed, one way we differentiate these from true cataracts is by shining a bright light into the eye; with nuclear sclerosis you'll see the iridescent reflection from the back of the eye, but with a cataract you won't. Since light still passes through, vision is still effective - perhaps it's a bit blurry, but I've yet to see a pet noticeably effected by it.

So, what can cause the delicate, highly-specialized lens structure to break down and lose transparency (i.e., form a cataract)? Genetics can certainly play a role, and there's a laundry list of breeds predisposed to cataract formation. Sometimes these are present at birth and sometimes they develop with age.

A true cataract. Note the completely
opaque lens.

Many other problems and diseases may cause cataracts as a secondary consequence - basically, anything that disrupts the environment within the eye can lead to cataract formation. Inflammation inside the eye (or uveitis) is a common culprit, and due to some quirks of structure the eye is a common place for inflammation to develop even when problems start elsewhere. This happens with many bacterial infections and autoimmune diseases, and it's another reason a complete physical exam by a veterinarian is so important in every animal -sometimes a good eye exam leads to discovering another problem, or vice-versa. Trauma to the eye, or (yikes) to the lens itself can certainly result in cataracts as well.

Vision loss is not the only potentially serious consequence of cataracts, however. When progressive, the lens may break down to the point that it leaks proteins into the rest of the eye, causing serious inflammation and even glaucoma - an extremely painful condition where pressure builds up inside the eye. Fortunately many cataracts are not progressive, but for this reason they should all be closely monitored by your veterinarian. Diabetic dogs merit special mention, as most of them will develop rapidly progressive cataracts due to differences in the way their lenses metabolize sugar. Considering this, all owners of newly diagnosed diabetic dogs get educated on how and why to monitor for cataracts. Likewise, any dog that suddenly develops progressive cataracts should be screened for diabetes.

While there is no proven medical treatment to slow or reverse cataracts, the same surgical procedure used in humans may be performed in pets. This involves breaking up the material in the lens, suctioning it out, and placing a prosthetic lens inside the remaining capsule. Obviously, it's a delicate procedure that requires lots of special (not to mention expensive) equipment and training, so it is only performed by veterinary ophthalmologists. Your family veterinarian should be able to direct you to a specialist and give you an idea of the costs in your area. The procedure has a high success rate for returning vision, but not everyone will be able to realistically afford the expense. Not every pet is a candidate, either - sometimes other problems exist that will prevent return of vision regardless. Fortunately, blind pets generally do quite well and have a good quality of life; your veterinarian and their staff should be able to offer tips for helping both you and your pet adapt if surgical treatment is not an option