The Itchy Dog: An Overview of Diseases

Chris Reeder, DVM, DACVD

Sometimes no matter how hard we try, a diagnosis of pruritic skin disease is frustrating.There are a few key questions and findings that may make life a little easier in dealing with the itchy dog.  The skin as an organ has incredible powers. Not mystical or magical, those are confined to brain along with neurologic pathways to control motion and physiologic/psychologic processes. No, the skin has its own special powers.  It acts as a physical barrier providing innate protection against the evils of the environment.  Skin stretches and can transition from taut to lose, thick to thin, it controls water loss and temperature regulation, it acts as a sensory organ and to many animals, camouflage to help hide from predators or stalk prey.  Skin truly is an incredible organ, though as incredible as it is, an Achilles’ heel does exist…..pruritus. 

Pruritus is derived from the Latin prurire meaning to “itch.”   It is defined as the desire or reflex to scratch.  Itching in the dog is one of the most common presenting complaints from owners to the general practitioner, yet one of the most frustrating and costly as well.  There is help, several key questions and findings may provide a starting point or diagnosis as to why a dog is itching.  Our first step is the question the owner about the dog’s condition:

-          Age of onset of the itching

-          Duration of the itching

-          Other animals in the household affected

-          Housed indoor, outdoor or both

-          Travel history

-          Current and previously fed diets (including human foods)

-          Seasonal history or exacerbations of itching

-          Previous medications, what worked and what didn’t work

-          Current flea/tick control products (other animals treated)

-          Number of bowel movements daily

-          Loose, runny stools or any vomiting

Many animals who have a food allergy will present as young dogs (<1 year of age) with loose or runny stools, >3 bowel movements daily and may be refractory to glucocorticoid use.  Other household animals are not affected and this is typically non-seasonal with itching as a constant feature.  Compare that to the typical dog with atopy (environmental allergies) and we see that most of those dogs present first between 1-4 years of age, have some seasonal pattern, respond to glucocorticoids with a reduction of pruritus and no other animals in the household are affected.  The author’s experience, along with many dermatologists, find that atopy is a much more common presentation than food allergy in roughly 90% to 10%, respectively.  We also see that food allergic dogs often have some compromise to the gastrointestinal barrier function.  This could be a history of intestinal parasites, Parvovirus enteritis, or any other disruption to the gut integrity.  What about a dog whose symptoms appears more atopic but is non-seasonal?  That could be a dog that is suffering from indoor allergens (dust mites, storage mites, human or cat dander, sheep wool, cotton, etc) which allergy testing may be a helpful tool in order to diagnose. 

Scabies can mimic food allergy and atopy very closely.  Other animals or even humans in the household may be affected with pruritus.  The typical approach to dogs with scabies is to identify a pinnal-pedal reflex.  This involves grasping the pinna between the thumb and forefinger of both hands and rubbing the skin together.  A positive response would involve the ipsilateral hind leg start scratching vigorously after a few seconds.  It has been reported that up to 80% plus of dogs with scabies exhibit a positive pinnal-pedal response and these are cases to empirical treat with an acaracidal therapy (e.g. Advantage-multi^® Bayer, Revolution^® Pfizer) which is usually an off-label dosing of one treatment every 2 weeks for 3 total doses.  Common areas affected with scabies infestation include: hocks, elbows, pinnae, groin and scrotum.  All animals in the household should be treated as some may serve as a reservoir even if not itching. 

Flea allergy is truly a hypersensitivity response. This appears as a dose-dependent phenomenon with the higher number of flea bites with salivary protein exposure thus resulting in an allergic response.  The number of bites to induce an allergic response varies with some animals showing no response even with hundreds of bites.  It is important to examine the dog, especially those with long coats, on the rump region.  A severe inflammatory response can be seen in dogs with a strong allergic response to fleas with moist pyoderma and excoriations predominantly over the dorsal lumbar region.  Another common finding in dogs with flea allergy is the discontinuation of flea control over the winter months.  Fleas overwinter indoors and continue to thrive, only at a slower rate than the warm and humid summer months.  Continued flea control for all animals in the household is a very effective means of controlling flea allergies.  Several topical formulations now have both flea prevention and heartworm prevention in a single dose application (e.g. Advantage-multi^® Bayer).  Bathing around the time of application of the topical spot-on formulations of flea preventative is another question to ask the owner.  Typical recommendations are to wait 48-72 hours after application to bathe a dog or use an oral flea preventative (e.g. Comfortis^® or Trifexis^® Elanco). 

   

Ringworm, is neither a ring nor a worm, the saying goes “if it looks like ringworm, it’s probably not” in dogs holds true.  Dermatophytosis in dogs usually presents with pruritus, hair loss, erythema and scaling.  Rarely does ringworm present as focal, circular patches of alopecia in dogs.  Various forms of ringworm can be present in dogs, geophilic, zoophilic, anthrophilic with the geophilic (soil) or zoophilic (animal) forms most common.  Microsporum gypseum is a geophilic dermatophyte whereas Microsporum canis is a zoophilic dermatophyte and the most common species seen in the dog and cat.  Occasionally multiple animals in the household may be affected and about 10% of humans can also have lesions which are typically pruritic.  A dermatophyte test media (DTM) culture is ideal to diagnose and speciate the type of dermatophyte present.  Fluconazole (5-10 mg/kg po daily) is the author’s treatment of choice for dermatophytosis.  Terbinafine (Lamasil^®, 30-40 mg/kg po daily) may also be used for refractory cases. 

Pruritus also damages the cutaneous barrier function both as, what we think is, a genetic dysfunction of the intercellular cement along with direct excoriations of the integument. This barrier defect has led to the development of many good products to help control and restore function.  Wipes, shampoos, lotions, balms and sprays have all been recently developed an are on the maket to help restore or improve skin barrier function in animals.  Shampoos have technology to even prevent bacteria/yeast from adhering to the skin surface (Virbac glycotechnology).  Pro-ceramides have been incorporated into sprays and shampoos to help repair damaged skin (phytosphingosine, Douxo^® (Sogeval)). 

Pruritus may have developed due to an allergic response to food, parasites or the environment and taking the time and understanding what to look for in these cases can make for a much more rewarding treatment outcome.  Many dogs need ongoing management for their atopy, need to be on flea prevention every 3-4 weeks ongoing or must be maintained on certain diets if food allergic.  Scabies is curable, though we do occasional see reservoirs in other household dogs or wildlife making further questioning an important part of the treatment.  Asking the right questions along with a thorough history and physical exam may help increase the correct diagnosis and decrease frustrations levels for the itchy dog. 

Pregnancy Termination in Companion Animals

by C. Scott Bailey, DVM, DACT

Despite much of discussion on the subject, there is still a great disparity in treatment protocols for mismated companion animals in the USA and elsewhere. Numerous treatment protocols are available. Ovariohysterectomy has the advantage of permanently removing the risk of an unwanted pregnancy. Medical treatments have varying side effects depending on the protocol selected, and depend on owner vigilance to prevent future pregnancies. Medical treatment is most often performed in early gestation or mid gestation. Pregnancy termination after fetal ossification (45 days) results in abortion of non-viable or poorly viable fetuses.

            Treatment choices should be guided by an animal’s actual risk of pregnancy. In dogs, a vaginal swab and cytologic evaluation provide 2 key pieces of information: 1) Detection of sperm heads on cytology can confirm exposure to a male, and 2) determination of estrus stage at the time or presentation. In a study involving 16 females with known breeding histories, Whitacre and coworkers demonstrated that sperm could be seen microscopically in 100% of cases within 24 hours of breeding and in 75% of cases within 48 hours of breeding, using a modified sampling technique. Determination of estrus stage is also a key component of determining the risk of pregnancy. Bitches with known or suspected exposure to a male during proestrus are at much lower risk of pregnancy than those exposed during estrus. Cytologic diagnosis of proestrus can be further confirmed with serum progesterone concentrations of <2ng/mL. As cats are induced ovulators, serum progesterone will likely be low in unexposed cats (<2ng/mL) and would rise after coitus in exposed cats.

Prior to any treatment, it is important to carefully consider options for treatment. Animals that are not intended to be breeding animals, do not have high risk-factors for spay-associated disease and which are not in show, should undergo ovariohysterectomy in early diestrus/pregnancy. This will prevent future unwanted pregnancies and may decrease the animals’ risk of several diseases, including pyometra, mammary and ovarian neoplasia. Animals which cannot be spayed may be treated medically with a variety of protocols.

Early pregnancy termination

            Several protocols have been proposed to medically treat bitches as soon as a mismating occurs. This approach is attractive, but may pose a greater risk to the animal and have lower success rates than other protocols. As a result, most reviewers have recommended against these treatment regimens.

            Estrogens have been widely used for this purpose in the past, but potentially severe side-effects should raise concerns. Several reports indicate significant health risks associated with estrogen treatment in dogs and cats, including an increased risk of pyometra, infertility and toxicity.

Pregnancy termination in mid-gestation

            In the dog, pregnancy can be readily diagnosed by palpation approximately 30 days after mating, whereas ultrasonographic examination can confirm pregnancy as early as 15-18 days after the LH surge (~10-20 days after mating). Embryos are easily detectable between day 22 and 25 after LH surge. In the queen, ultrasonographic pregnancy diagnosis can be achieved as soon as 11 days after mating and the embryo becomes visible by 14 or 15 days after mating.

            At this stage, embryonic fluids and tissues are resorbed by the uterus and few clinical signs are expected in response to medical intervention. A bloody discharge may be seen in bitches and queens after approximately 30 days. Abortion (fetal expulsion) occurs after 40-45 days, when fetal ossification is underway.

Prostaglandins

Natural prostaglandins can be used to terminate pregnancy beginning 5 days after ovulation, however prior to 25 days, higher doses are required than later in gestation. Hospitalization and careful monitoring of animals are recommended to control side-effects, which tend to be more severe early and diminish during the course of treatment. Side effects may be minimized by using low doses of prostaglandin, or by starting with a lower dose and gradually increasing it. It should be noted that low doses may not induce permanent luteolysis, resulting in loss of only some pups or fetal death followed by mummification. The synthetic prostaglandin cloprostenol has also resulted in effective pregnancy termination, with few side effects.

Dopamine Agonists

            In both the bitch and queen, prolactin plays a necessary luteotrophic role in pregnancy maintenance. Progesterone can be reduced or eliminated during late pregnancy by administering a dopamine agonist, which inhibits endogenous prolactin secretion.³² However, treatment success for pregnancy termination has been inconsistent in both dogs and cats and dopamine agonists alone are rarely used in companion animals.

Combined Prostaglandin/Dopamine Agonist Regimen

            Extensive work by Verstegen and coworkers, demonstrated that a dual approach to pregnancy termination results in reliable efficacy in mid gestation. Low doses of either natural or synthetic prostaglandins result in luteolysis, while dopamine agonists inhibit prolactin release. In a series of studies, administration of cabergoline and cloprostenol resulted in fetal resorption with minimal discharge or unwanted drug-effects in both dogs and cats. Treatment was continued until ultrasonographic confirmation of fetal demise. The above protocol has several distinct advantages over other protocols described: Both prostaglandins and dopamine agonists are readily available in the USA. The combined luteolytic and antiluteotrophic mechanisms decrease dosages of each drug, substantially reducing side effects. The protocols can be instituted around day 25 and result in resorption prior to fetal ossification, when most animals would abort formed fetuses. The use of orally administered dopamine agonists and long-acting, synthetic prostaglandins eliminates the need for frequent examination and hospitalization.

Conclusions

In conclusion, risk for pregnancy should be determined at the time of mismating and ideally pregnancy should be confirmed prior to treatment in order to avoid unnecessary and potentially harmful medical side effects. Treatment choices should be based on the animal’s stage of gestation and availability and should be tailored to minimize side effects as much as possible. A treatment onset between 25 and 30 days and combination of two drugs, including a prostaglandin and dopamine agonist minimize drug dosage and side effects while inducing fetal resorption rather than abortion.