Ehrlichia canis - Neorickettsia risticii - Anaplasma phagocytophilum
Anaplasma platys - Ehrlichia ewingii & Ehrlichia chaffeensis

First, we have to deal with a matter of name changes. The causative agents of Canine erhlichiosis (E. canis), Canine granulocytic ehrlichiosis(E. ewingii), and Human monocytic ehrlichiosis (E. chaffeensis) remain what they were, but science has changed the names of the organisms we've known as E. risticii, E. equi and E. platys to better reflect their natural relationships.

Erhlichia risticii has become Neorickettsia risticii.
Ehrlichia equi has become Anaplasma phagocytophilum.
Ehrlichia platys has become Anaplasma platys.
You'll see each of these three referred to by both the old name and the new one as you read on. For convenience, however, I'll continue to use "ehrlichiosis" as a generic term for them all.
According to the Erhlichiae Research Laboratory at Ohio State College of Veterinary Medicine, "New genus Ehrlichia, except for E. ewingii ...infects monocytes and macrophages. E. ewingii infects granulocytes.... The genus Anaplasma group infect granulocytes, platelets, red blood cells. The Neorickettsia group infects monocytes and macrophages. N. risticii in addition infects intestinal epithelial cells and mast cells."
Note: "ehrlichiosis" is the disease; "Ehrlichia" is the organism.
The Stages of Ehrlichiosis
Ehrlichiosis (E. canis is the most studied) has three stages. The acute stage is brief and the symptoms are easily missed; it may appear as if the dog has a mild and passing viral infection: snotty nose, diarrhea, fever, a general lack of his usual oomph. In a stoic dog especially, a change in behavior may be the only alert he gives you to get him to the vet.
It's in this stage that the outlook for a cure is best. Very early on, however, testing is probably useless; until ten days to two weeks after infection, the immune system will not have had time to make sufficient antibodies for the tests to detect.
The acute stage over, the disease passes into the subclinical stage. This simply means a stage in which no symptoms are present. Cure, or at the very least, containment of the disease so that it cannot progress, is still a good possibility in this stage which may last for years.
If the disease progresses to chronic, the outlook is grave, particularly in E. canis and N. risticii. Symptoms show up with a vengeance at this point. A lengthy, probably still incomplete list of symptoms and the diseases for which ehrlichiosis is often mistaken, can be found in the right column.
Dr. Cynthia Holland, Ph.D has written an excellent and brief article on the importance of titers in determining treatment for canine erlichiosis that addresses the various stages of the disease. Dr. Holland is an expert on tick-borne disease and she states emphatically: "The magnitude of antibody titers resulting from infection with Ehrlichia canis is directly correlated with the chronicity of the disease (i.e., the length of time the dog has had it). This information is extremely important in determining the treatment protocol since dogs which have been chronically infected for some time will require a more rigorous and lengthy treatment with doxycycline and, possibly, imidocarb in order to successfully clear the infection. This is in contrast to treatment during the initial acute phase, which generally requires only 3 weeks of doxycycline therapy."
Dr. Ed Breitschwerdt of NC State once noted in a discussion of Rocky Mountain Spotted Fever, which is unfortunately no longer on the web, that distemper, and erhlichiosis can present very similar signs in a young dog.
Misdiagnosis which delays or prevents a correct diagnosis of TBD is unhappily common.
Think hard before you breed a bitch that has had ehrlichiosis
There is strong reason to believe that erhlichiae may not be completely eradicated by treatment, that at least some of the organisms may be able to hide, much like Lyme spyrochetes, waiting for conditions to become favorable to show up again. In one case I know of, E. canis was found in the ovaries of a dog spayed after treatment, though post-treatment blood tests showed a negative titer. A clinical test done on infected ponies confirmed that N. risticii causes fetal abortions and can infect foals before birth. Anecdotally, N. risticii has also been known to cause prenatal infection in dogs, and while transmission through sperm hasn't been proven as far as I know, it's something to think about before using a dog at stud.
Bringing pups into this world infected with ehrlichiosis, especially if they are German Shepherd Dogs or Doberman Pinschers, dooms them to suffering somewhere down the road and their people to real heartbreak. Our dogs and the people who love them deserve better of us.
Ehrlichiosis canis - Canine monocytic ehrlichiosis
Named after Dr. Paul Ehrlich, who discovered the causative organism of ehrlichiosis, E. canis, the most common form of this disease in dogs, cripples the immune system by making it impossible for the white blood cells known as monocytes to replicate correctly or, in the end, to reproduce themselves at all.  It has gotten more attention from researchers than any other canine tick-borne disease, probably because of the number of military dogs in Vietnam that fell victim to what was then called Idiopathic Hemorrhagic Syndrome or Tropical Canine Pancytopenia. In a two and a half year period, it was the direct cause of death for 220 dogs, primarily German Shepherd Dogs, and a "contributing reason for the euthanasia of many others".
Yet, despite that, getting a diagnosis can be difficult because E. canis can be frustratingly non-specific at first, nothing special, nothing to get alarmed about. If a dog is brought in to a clinic with a number of vague complaints, because he's droopy, not eating very well, vomiting bile or just "ain't doing right", those are complaints veterinarians hear all the time and they don't really raise a red flag for TBD. For that reason, I can't stress enough how important it is for veterinarians to read the webpage that first brought clear, comprehensive information about this disease to anyone who has access to the internet, Ehrlichiosis, a Silent and Deadly Killer, particularly the foreword by Dr. Ibulaimu Kakoma, DVM PhD and the section specifically addressed to them.
"Perhaps the most critical thing for the clinician to remember is to look at the big picture. Does a client's pet really have several ailments affecting different systems, or could it be suffering from ehrlichiosis which, in essence, affects all systems?"
Progression of the Disease
In the acute stage, fever (pyrexia), diarrhea caused by inflammation of the intestines (enteritis), swollen lymph nodes (lymphadenomegaly) and enlargement of the spleen (splenomegaly) are common symptoms. There may be an increase in white blood cells. If you suspect your dog may have erhlichiosis, have your vet check your dog's eyes. Ocular manifestations include uveitis, retinal disease and corneal opacities.
When the disease goes into the subclinical stage where no symptoms are present, E. canis burrows in, generally sequestering in the spleen, and undermines any of a number of organs but the bone marrow, where production of the red blood cells, white blood cells and platelets takes place, is at some point a primary target. "The only hint that Ehrlichia are hiding is a somewhat reduced platelet count and/or elevated globulin level on a blood test." Laboratory findings during this stage may also include mild thrombocytopenia and a positive antibody titer; slightly decreased packed cell volume (fewer red blood cells) or leukocytes (white blood cells).
Undiagnosed and untreated, the disease sooner or later moves on to the chronic stage, triggered, perhaps, by stress, trauma, an unrelated infection, or just a body caving in to exhaustion. In the most extreme example I know of, Adam, an Australian Shepherd, became visibly sick for the first time at five o'clock one afternoon and was dead by two in the morning despite a veterinarian working over him for hours, trying to save him after being rousted out of bed by the dog's frantic owner. The vet said afterward that it was clear to him that Adam had been harboring infection for some time, possibly years.
According to a Purdue University newsletter, how severe the disease becomes depends on the dog’s age, as young dogs are more likely to be infected; what kind of ehrlichiosis it is; whether or not the dog is already sick and what kind of dog it is. It goes on to say that dogs with a normal, healthy immune system (immunocompetent) may be able to shake off ehrlichiosis but that the organism persists in the cells of most dogs and progresses to a chronic stage that might be mild or severe.
I have some trouble with the idea of 'mild chronic ehrlichiosis'. It seems to hint that the dog can survive well enough without treatment even though he's infected. Don't even think it. Failure to treat is asking for the worst possible outcome, especially for German Shepherd Dogs.
Dogs generally seem to show a serious loss of condition when the disease reaches the chronic stage. I've seen dogs that died of it described as 'emaciated'. A dog may cough or have trouble breathing. Sooner or later, the dog may go blind. He may develop an excessive thirst and urinate more than he normally would, signaling kidney involvement. He may develop a disorder of the eye, brain or spinal cord. Nothing seems to be beyond this disease.
Changes in the blood may show up as nonregenerative anemia, thrombocytopenia (an abnormal decrease in platelets) or leukopenia (an abnormally low number of white blood cells). In the severe chronic stage, secondary immune-mediated hemolytic anemia (IMHA) may cause a dog to have a hemolytic crisis in which destruction of the red blood cells is so rapid that the body just can't make replacements fast enough. Or the dog may develop pancytopenia, a deficiency of all the blood cell components.
When the immune system turns on itself as it does in an auto-immune disorder, sometimes the only recourse is to use a corticosteroid such as prednisone or prednisolone to suppress it. Since the immune system is already under attack by E. canis, the vet has a fine line to walk in determining how much prednisone will be enough and not too much. Prednisone, given to a dog that has undiagnosed ehrlichiosis, can be dangerous but in the right hands, if the disease has been recognized and is being treated, this drug can be life saving.
Cross infection with other tick-borne diseases is common.
Neorickettsia risticii - formerly E. risticii                       
Ehrlichia risticii, now known as Neorickettsia risticii, is familiar to horse owners as the causative agent of Potomac Horse Fever in the East and Shasta River Crud on the West Coast.  For a long time, the vector could not be identified but we now know that the organism causing this disease is incubated in the larvae of flukes that live on certain water snails, is transmitted to caddis flies and other insects that ingest them, then is passed by these insects to the dog, presumably when he unintentionally eats them or drinks them in with water from rivers that contain these snails.
E. risticii was renamed to reflect the disease organism's close kinship to the organism that causes Pacific Salmon Poisoning Disease (Neorickettsia helminthoeca).
 I was tempted to place N. risticii first on this page, to be honest, because it killed my dog but also because there is no protection against it.  There is a vaccine for horses but there is no vaccine for dogs and no way to prevent a dog ingesting an insect carrying this disease. 
If E. canis affects monocytes and macrophages, N. risticii adds intestinal epithelial cells and mast cells to that list and appears to be much more severe, more resistant to treatment, more difficult to contain or to overcome than other forms of TBD.  Since German Shepherd Dogs appear to suffer more severely than most other breeds from both E. canis and N. risticii, a timely diagnosis is especially critical for them.
I believe that any dog that is already ill when this disease is contracted, or was infected in the womb as Anne McGuire's Jasper was, is in serious trouble.  Anne recounts in detail the battle she waged and won against chronic N. risticii on Jasper's website and provides a lot of useful information that I would highly recommend you read.  It's rumored that one other person has successfully conquered chronic N. risticii in her dog.  I've never heard of anyone else doing it. 
In 1994, Dr. Ibulaimu Kakoma and his colleagues "reported serologic evidence of over 100 cases of atypical canine ehrlichiosis with three fatalities."  Atypical canine erhlichiosis.  It acted like E. canis yet tests said it wasn't.  What they found instead was E. risticii (N. risticii), the agent of Potomac Horse Fever, not in horses but in dogs. 
Clinical signs for six of these dogs were reported and ranged from lethargy and vague signs of abdominal discomfort to persistant bleeding, polyarthritis (inflammation of several joints) and hind end paralysis.  Bloodwork also showed results that varied from dog to dog:  the time it took for some dogs' blood to clot was prolonged, some became anemic, some developed thrombocytopenia (low platelets), some had abnormally high concentrations of calcium in the blood.  Some dogs responded well to treatment with tetracycline, some dogs didn't respond at all.  Dr. Kakoma proposed calling this organism isolated from the dogs' blood E. risticii subspecies atypicalis
Since then the ehrlichiae have been regrouped and some renamed, but the "common natural host" of N. risticii was, and still is, listed as the horse.  Evidently N. risticii is still not considered a serious threat to dogs.  Most likely it isn't - except to those breeds hardest hit by it, the working and sporting dogs most likely to encounter it.
N. risticii is contracted close to rivers and in wetlands.  Tracking is a dog sport I love, at which my dogs have excelled, and I've often tracked my dogs in wetlands adjacent to the Chattahoochee River and sometimes near the Oconee River, both in Georgia.   I am personally convinced that snails hosting the larval flukes which carry N. risticii are present in one or both of these rivers and that Thunder was infected while we were near one or the other.  My older dog, Traveler, escaped it but whether that was luck or simply that he was an adult while Thunder was very young and more vulnerable, I'll never know.
Cross infection with other tick-borne diseases is common.
Anaplasma phagocytophilum
Once known as Ehrlichiosis equi A. phagocytophilum and Human Granulocytic Erhlichiosis (HGE) now share classification as A. phagocytophilum as they are so closely related. 
A. phagocytophilum can cause painful arthritis in several joints, lethargy, high fever, loss of appetite, vomiting and diarrhea.  Less commonly, a dog may have neck pain or seizures.
Lester, Breitschwerdt, et al. report in this abstract from the Canadian Veterinary Journal that: "Canine anaplasmosis caused by A. phagocytophilum varies from a subclinical infection to an acute febrile condition accompanied by anorexia and lethargy. Central nervous system dysfunction and lameness have also been recorded in dogs. Based on reports to date, anaplasmosis appears to cause a less severe disease in dogs than does infection with E. canis, E. chaffeensis, or E. ewingii.  Lethargy, accompanied by fever, appears to be documented consistently, and the lethargy is often disproportionately severe in comparison with the general lack of abnormalities documented on physical examination. Although most dogs have a mild thrombocytopenia, anemia is uncommon and changes in the leukocyte numbers are variable. Elevated ALP activities have been reported in dogs with anaplasmosis. Recent serologic assessments in California indicate that many clinically normal dogs have titers to A. phagocytophilum; this suggests that cases may be subclinical or that the disease may be underdiagnosed."
(By the way, the dog discussed in that abstract was from Vancouver Island in Canada and had never left the island.  Obviously, TBD does exist in Canada.)
A. phagocytophilum infects neutrophil granulocytes, as does E. ewingii, so both may be referred to as canine granulocytic ehrlichiosis or CGE.
The pathogenesis (origin and development) of polyarthritis, observed more often with infection by granulocytic ehrlichiae, arises from hemarthrosis (hemorrhage of blood into a joint) and immune complex deposition into the joints. (Immune complexes are formed by bound-together disease antigens and antibodies produced by the dog.)
Further reading on Anaplasma phagocytophilum: 
An update on anaplasmosis in dogs:  Rick Alleman, DVM, PhD
Site Index    
Symptoms of Ehrlichia canis

E. canis is the most common form of ehrlichiosis in dogs to date, therefore the most is known about it, yet this list of symptoms is probably far from complete.
This list of the symptoms of erhlichiosis, compiled by Susan Netboy and Judy Ellam, was given to me by Ellie Goldstein, a long-time member of Tick List. Ellie was Adoption Chair of We Adopt Greyhounds (WAG) for many years and "talked ticks" to adopters as publisher of that organization's newsletter, Wag Tales. Susan Netboy, Judy Ellam and Lynda Adame were instrumental in bringing information about tick-borne disease in Greyhounds to the Internet, and benefitting the owners of every breed of dog in the process.

intermittent fever
intermittent loss of appetite
total loss of appetite
gradual loss of body condition (esp. along the spine and around the eyes)
viral tumors on the face/mouth/muzzle
hemorrhaging even when the blood count looks normal
clotting problems
low or high calcium levels
muscle wasting
skin infections
neurological signs (repetitive obsessive actions or palsy)
low platelet count
urine too alkaline
hyper-reflective eyes
low white blood cell count
bleeding from nose or eyes
ocular signs
kidney failure
increased thirst and urination
neck or back pain
bleeding under the skin or a rash
swelling of the legs or joints
enlarged lymph nodes
irreversible bone marrow suppression
For more information on the symptoms & treatment of ehrlichiosis, these websites are excellent.
Ehrlichiosis, a Silent and Deadly Killer by Jan Hendricks and Bob Wilson, with a foreword by Ibulaimu Kakoma, DVM PhD.  Note:  This is an earlier version of the page which seems to have disappeared from the Internet.  It is, however, still a highly recommended read.
Jasper's Canine Tick-borne Disease Information Page by Anne McGuire
antibody: any of a large variety of proteins normally present in the body or produced in response to an antigen. The neutralizing of antigens by antibodies is called the immune response.
antigen: in this context, bacteria introduced into the body by the tick as it feeds. When they are detected, the immune system begins to create antibodies to fight the intruders.
Image and definition of an antibody
"An antibody is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. This is because at the two tips of its "Y", it has structures akin to locks. Every lock only has one key, in this case, its own antigen. When the key is inserted into the lock, the antibody attaches, tagging the microbe or an infected cell for attack by other parts of the immune system or by directly neutralizing its target (i.e. blocking a part of the microbe that is essential for its invasion and survival). The production of antibodies is the main function of the humoral immune system."
cytoplasm: the protoplasm of a cell, excluding that of the nucleus. Most of the chemical activities of the cell occur here.
protoplasm: the entire contents of a live cell.
White blood cells (WBCs): cells which circulate in the blood and lymphatic system and harbor in the lymph glands and spleen. They are part of the immune system responsible for directly (t-cells and macrophages) and indirectly (B-cells producing antibodies) attacking foreign invaders of the body.
leucocyte: generic term for a white bloodcell. 
monocyte: one of 3 types of white blood cells.  Monocytes are precursors of macrophages.
macrophage: macrophages play an important role in the killing of some bacteria.  They release substances which stimulate the immune system and are involved in antigen presentation.  The name means "big eater".
Processing and presentation by the macrophage marks the antigen to make it recognizeable to a type of
T-cell often called a "killer cell" so that it will destroy the antigen.
phagocyte:  a cell that engulfs and digests debris and invading microorganisms.  The main mammalian phagocytes are neutrophils and macrophages.
neutrophil:  a granulocyte, the most abundant phagocytic white blood cell.  These granulocytes are meant to destroy invasive micro-organisms but, paradoxically, are themselves the target of TBDs such as A. phagocytophilum and E. ewingii.
T-cell: A principal type of white blood cell that completes maturation in the thymus and that has various roles in the immune system, including the identification of specific foreign antigens in the body and the activation and deactivation of other immune cells. Also called T lymphocyte.
granulocyte: a white blood cell with very evident granules in the cytoplasm.
red blood cell: A cell which specializes in oxygen transport.  Too few result in an insufficient supply of oxygen to the organs and tissues and is called anemia.
platelet: A small cell shaped like a disk found in blood plasma that promotes blood clotting and stops bleeding by repairing small breaks in blood vessels. Also called a thrombocyte.
epithelial cell: the epithelium is the covering of internal and external surfaces of the body, including the lining of vessels and other small cavities.  An epithelial cell is one of the closely packed cells forming the epithelium.
mast cell: a large connective tissue cell that contains histamine and heparin and serotonin which are released in allergic reactions or in response to injury or inflammation.
thrombocytopenia:  an abnormal decrease of platelets (which promote blood clotting) in circulatory blood.  The name comes from the old word for platelet (thrombocyte) and the suffix -penia, which means "too few".
pancytopenia: a deficiency of all cell elements of the blood.  Also known as aplastic anemia, a condition that occurs when the bone marrow stops making enough red and white blood cells.  (See TBD Related References for an important link on the successful treatment of a dog with severe chronic pancytopenia caused by E. canis.)
blood protein is divided into two components:  albumin, an important carrier protein and globulin, every other blood protein including antibodies.
IMHA:  Immune-Mediated Hemolytic Anemia.  Destruction of the red blood cells due to antibodies which stick to the RBCs and cause the body to react as if they are enemies.
hypoplasia:  the incomplete development of an organ or tissue. 
pyrexia: fever
enteritis: inflammation of the intestines, especially the small intestine.
immunocompetent: able to recognize and act against invading antigens
secondary:  a disease that follows and results from an earlier disease.  Secondary IMHA, then, occurs when the immune system is already affected by another disease.
prednisolone: prednisone which has already been converted for use by the liver.  Conversion is a trivial chore for the liver, according to Dr. Tom Beckett, so the distinction is not significant except, perhaps, for a dog with impaired liver function.
Medical Definitions
A Corgi with Anaplasma Phagocytophilum
  This is Calvin
Janry's Calvin Klein was one of the top 25 agility dogs in 2000.  Now, he can no longer walk without a cart due to severe neurological damage from chronic E. equi (Anaplasma phagocytophilum).   He has ongoing periods of anemia and thrombocytopenia and has come close to death several times but both Calvin and his owner, Diane, are fighters and neither of them is ready to give an inch in their fight against the disease that has cost him so much but still hasn't managed to take away his joy in life.
On the 20th of May, 2007, this valiant fighter lost his last battle.  He went with great dignity, deeply loved.
(For anyone who might need a dog cart, there are links to cart manufacturers on the General References page.)
Anaplasma platys
A. platys is unique in that it specifically targets the platelets that stop bleeding and promote clotting. After infection, platelet counts drop dramatically over a 3 to 4 day period, then the number of parasitic organisms diminishes and over another 3 to 4 day period, the platelet count returns to normal. Then the cycle begins again.
So, severe thrombocytopenia that comes and goes in cycles is the hallmark of this disease which has few other symptoms, though mild fever and small, black and blue spots (hemorrhages) in the skin or gums may show up in the acute stage.
Over time, A. platys gradually goes away unless there is a cross infection with another type of ehrlichiosis or B. canis to aggravate it.
Caution is necessary during surgery to prevent a dog with A. platys hemorrhaging.
The PCR test has been considered the most reliable for detection of A. platys.

Ehrlichia ewingii
E ewingii produces clinical signs similar to those of A. phagocytophilum; fever, anorexia and thrombocytopenia are often seen. Changes in the blood are like those in E. canis.

Unlike E. canis, but like A. phagocytophilum, polyarthritis (swelling, pain and lameness in several legs) is common in cases of E. ewingii. Dogs may be stiff and reluctant to get up. Often, the neutrophils (one of two main cells that engulf and digest debris and invading microorganisms) become inflamed.
From the USDA Agricultural Research Service:  Although no cases of E. ewingii infections have been reported for the state of Texas, this study presents conclusive evidence of the presence of this infective agent in Texas, and it also is the first record of E. ewingii infected ticks occuring in any state in the U.S. other than North Carolina, Florida or Missouri, where the linked study concludes that it may be the main cause of ehrlichiosis in dogs.
More recently, E. ewingii has also been identified in northeast Oklahoma and northwest Arkansas where it may also be the primary agent of canine ehrlichiosis.
Ehrlichia chaffeensis
E. chaffeensis is found in humans for the most part and isn't seen much in dogs. I can find very little on it other than that it is carried by Amblyomma americanum and, like E. canis, infects monocytes.
See also the TBD References page for more links to information on ehrlichiosis.
How soon can a dog return to tracking, agility, lure coursing, hunting or any of the things that you and he love to do together?