A "tic" of prevention for canine ehrlichiosis

Oct 14, 2011

During the Vietnam War, as many as 1,600 military dogs were deployed in Southeast Asia. Many of these dogs, particularly the more susceptible German shepherds, became ill with a foreign disease that they had never been exposed to before: canine ehrlichiosis.

Signs in these dogs included bleeding, anemia, high fevers and lethargy. Many military dogs in Vietnam died from this disease. At that time, canine ehrlichiosis was not considered to be present in the U.S. However, despite enforcing strict criteria regulating the return of military dogs, this canine disease is now one of the most common infectious diseases in dogs in the U.S.

Canine ehrlichiosis is normally diagnosed in dogs that live or work in areas inhabited by the brown dog tick.

This disease only affects domestic and wild canines.

Although more common in Texas, Oklahoma, Arkansas, Louisiana and Tennessee, ehrlichiosis is now found throughout the U.S. It has become commonplace to diagnose farm and ranch dogs with ehrlichiosis in rural areas with high concentrations of disease-infected ticks. It can also be seen in city dwelling dogs.

Canine ehrlichiosis, a rickettsial organism, is transmitted by the brown dog tick. This tick lives in all 50 states. Dogs and wild canines are the primary host for this tick although they can be found on other mammals and wildlife. This tick has a cosmopolitan distribution, residing in tropical or temperate climates. Brown dog ticks are also happy to live indoors and can take up housekeeping in kennels, pens, homes, barns and other structures. Consequently, these ticks can be found in colder climates. Since brown dog ticks are not always seasonal parasites, ehrlichiosis is not necessarily a seasonal disease.

The mobility of the canine population and increased numbers of ticks, which is multifactorial, has impacted the prevalence of all tickborn diseases in the U.S.

Changes in agricultural practice since the 1930s, for example reforestation after the Dust Bowl, have increased habitat for ticks.

Wildlife conservation practices have created a resurgence of tick hosts. Additionally, some tick species benefit from warmer and moister weather, therefore climate changes in North America can affect their reproduction and spread.

Recent natural disasters in the U.S. have facilitated movement of wildlife and disease-carrying ticks. Displaced or relocated dogs after Hurricane Katrina introduced some infected dogs to new habitats. This year’s abundant rain and snowfall in many areas of the U.S. has been favorable for increases of many tick populations.

Texas Department of State Health Services conducted a poll of veterinarians, animal control officers and Texas AgriLife agents in northwest Texas which suggested regional dry conditions created significant decreased tick populations in rural areas. However, increased tick loads were reported, primarily within towns and cities, where moisture was available on lawns, etc.

The brown dog tick becomes infected after ingesting blood from a canine containing the ehrlichia organism. The infected tick then transmits the disease through bites to other dogs. The incubation period for the disease is eight-20 days. ehrlichiosis has three phases: acute, subclinical and chronic. These phases are not necessarily present in all animals.

During the acute phase of infection, dogs exhibit nonspecific signs including fever, loss of appetite and depression. Working dogs may still have their ‘try,’ but just flat run out of steam. Nose bleeds and anemia occur because the ehrlichia organism parasitizes some of the cells that are important for blood clotting. This abnormality, termed thrombocytopenia, can often be seen on blood work.

Untreated dogs in the acute phase may resolve spontaneously. However, this can lead to subclinical phases lasting two to four months where these dogs are still infected with the organism, but seem perfectly happy and healthy. Without apparent signs of illness in this phase, it’s uncertain how many infected dogs progress to become chronic cases. The length of time for animals to present with signs of chronic ehrlichiosis after the initial infection is not always clear. Subclinical phases can last for two months or up to several years if the animal is not stressed or immunosuppressed.

Symptoms associated with chronic ehrlichiosis can be mild, moderate or severe. In the mild chronic phase, dogs exhibit vague symptoms including weight loss, depression and anorexia. Shifting leg lameness is common due to joint and/or muscle inflammation caused indirectly by the organism. Many chronic cases exhibit more severe signs and could require blood transfusions.

Chronic ehrlichiosis can also affect the gastrointestinal, neurologic or ocular systems, therefore mimicking many diseases. Organ failure and development of coinfections related to compromised immune systems may potentially occur. It can be fatal in the occasional case.

A positive antibody titer to ehrlichiosis in dogs typically confirms the disease in the acute phase. There is a commercial diagnostic kit available for use in veterinary clinics confirming ehrlichiosis that gives immediate results. Some subclinical dogs may not test positive during this phase. This diagnostic kit also tests for heartworms and two other tickborn diseases, Lyme disease and canine anaplasmosis.

Dr. Susan Bozeman owns a small animal veterinary practice in Lubbock, TX, and has practiced in the area for over 30 years. She lives in nearby Idalou where her family farms and ranches and has a good perspective on the prevalence and clinical behavior of ehrlichiosis in her urban as well rural patients.

“The number of ehrlichiosis cases we see in my practice is definitely related to the number of ticks. Years when tick populations are high, we might diagnosis three to four cases per week,” explained Bozeman. “But with it being so dry and ticks are scarce, I only diagnosed about three or four cases of ehrlichiosis all summer.”

“I probably see the chronic cases more in rural and shelter dogs. I think monthly flea and tick control is more common in town dogs that live with their owners; that helps minimize the disease in those patients. Country dogs seem to get left out of the tick preventative routines, so I stress the importance to these owners of keeping their dogs free from ticks. I also recommend to all my clients annual testing helping identify the early stages of the ehrlichiosis so we can treat those dogs and reduce the number of chronic cases. With that same ‘inclinic’ test,’ we can also pick up Lyme, Rocky Mountain spotted fever and anaplasmosis.”

History of tick exposure is very important for veterinarians examining symptomatic dogs . For example, hunting or stock dogs may travel to work in regions with populations of diseasecarrying ticks. History is also important for diagnosis in symptomatic dogs that have originated from other areas of the U.S. An owner’s knowledge of their dog’s previous infection with ehrlichia, even if it occurred several years prior, is imperative for veterinarians diagnosing chronic disease.

Doxycyline or tetracycline are the antibiotics used to treat ehrlichiosis. Improvement of clinical signs may be noticed within 24-48 hours. It’s important to treat animals for 30 days to help clear the organism and minimize their chances of progression to subclinical and chronic phases. Dogs in the chronic phase of ehrlichiosis generally require a prolonged regimen of antibiotics, up to eight weeks, in addition to supportive care. Chronic Ehrlichiosis is oftentimes considered ‘treatable’ versus ‘curable’ due to the difficulty in clearing the organism from the dog’s body.

The key to prevention of ehrlichiosis is tick control. Monthly ‘spot-on’ products for small animal parasite prevention are generally effective against ticks when administered according to label directions. Tick collars also have a role in parasite control, some having threeto six month-efficacy and water resistance. Consequently, ranch dogs cooling off in a tank, bird dogs retrieving ducks, or Jack Russell terriers diving into the kiddie pool can maintain protection against ticks.

Awareness of other tickborne diseases such as Lyme and Rocky Mountain spotted fever is heightened because of their ability to infect people and other animals. But dog owners also need to be familiar with canine ehrlichiosis, its prevalence in the area, the clinical symptoms and its prevention. It’s also important to understand that current absence of ticks on a suspect ehrlichiosis dog does not rule out disease in dogs with a history of prior tick infestation.

Many canine ailments can produce the ADR syndrome (Ain’t Doing Right) in dogs, but good tick control can help move ehrlichiosis to the bottom of the suspect list. — Ginger Elliott, WLJ Correspondent