Ehrlichiosis and anaplasmosis are bacterial diseases dogs get that are spread by tick bites. The disease can be a little different depending on the individual bacterial species, but treatment is generally the same. Certain species of ehrlichiosis and anaplasmosis can be infectious to humans as well, generally through a tick bite.
Bacterial species that cause ehrlichiosis are Ehrlichia ewingii, Ehrlichia chaffeensis, and Ehrlichia canis. Species that cause anaplasmosis are Anaplasma phagocytophilum and Anaplasma platys.
Ehrlichiosis and anaplasmosis look similar when your veterinarian gives a physical examination. Low platelet count (thrombocytopenia) is common, which may lead to bruising or abnormal bleeding. Ehrlichiosis and certain species of Anaplasma can also cause a low red blood cell count, what we call anemia, which can appear as pale skin and gums or cause a pet to act tired. Swollen or painful joints may also be seen with ehrlichiosis and some anaplasmosis infections. All of these symptoms can occur suddenly, or they may happen off and on over time.
Because these diseases are caused by ticks and can lead to pretty serious illnesses in dogs and people, testing methods were created to quickly screen for these organisms in pets. The most common test is an IDEXX Snap® test, which can be performed in minutes by veterinarians in general practice clinics or hospitals. Snap tests use a small blood sample to determine if the pet has created antibodies against Anaplasma spp. and Ehrlichia spp. Antibodies are proteins in the blood that are created when a pet's body is exposed to bacteria and viruses so as to help fight that infection. Each antibody is made specifically for the virus or bacteria the body was exposed to. Even after the infection is gone, these antibodies will remain in the blood stream. This is partly why people and pets become immune to certain illnesses after they get sick.
Unfortunately, Snap tests are not 100% accurate and results can be a bit confusing. Tests can sometimes be negative even if the pet has the infection. This could be because the pet was only recently infected and hasn’t had time to build up enough antibodies to make the test positive.
Sometimes Snap tests are positive when a pet is not infected. This is usually because the pet was exposed to the bacteria from a tick bite. Even though the pet didn’t develop an infection, their body made enough antibodies to protect itself just in case. Remember that positive Snap tests only mean that antibodies to ehrlichiosis or anaplasmosis are in the bloodstream. The tests can’t tell whether the bacteria themselves are in the pet’s body.
Snap tests can also be positive if a pet is a carrier of infection, meaning they are infected but not showing any symptoms. Many carriers never show signs of infection. It is not fully clear why this happens, which can be confusing and worrisome for many pet owners.
A history of tick bites, symptoms, and abnormal findings on a physical exam need to be taken into account to determine if the pet is truly infected or not. Blood tests to check the platelet and red blood cell count can be done to see if the pet is experiencing active infection (as opposed to being a carrier of infection). Additional testing can be sent out if a true diagnosis is needed. These types of tests can also determine which specific type of anaplasmosis or ehrlichiosis infections the pet has.
A pet with a normal checkup who shows no symptoms but has a positive Snap test can be monitored. This means you will need to keep an eye open for new symptoms and physical changes, but you don't need to do anything else. In some cases, if the pet’s tests and symptoms are suspicious for an active infection your veterinarian may prescribe a course of antibiotics. Your veterinarian will help you decide whether additional testing is necessary.