Ehrlichiosis
Ehrlichia are microscopic organisms of the Rickettsial family which are small enough to invade and damage individual cells in the body especially the blood cells. Ehrlichia canis (E.canis), Ehrlichia platys (E.platys), and Ehrlichia risticii are the most important members of this group. These organism are spread between animals by Rhipicephalus sanguineus (brown dog tick) when they feed. Dogs and cats can both become infected and there is evidence that humans may also be able to contract the disease.

The disease has a long incubation period (time from infection to symptoms) and may progress slowly leading to delays of up to 2 months after initially becoming ill before animal is presented for examination. After a 1-3 week incubation the disease begins to go through a series of 3 possible stages:
Acute
Ehrlichia spread to the spleen, liver and lymph nodes (glands). All these organ increase in size in response to the infection. The endothelium (lining of the veins) is infected and this causes an increased tendency to bleed. As a result a mild anemia (reduced red blood cells ) occurs and a thrombocytopenia (decreased numbers of platelets (cells involved in blood clotting) The platelets are being used up faster than they are produced, in an attempt to form small clots around each of the leaking blood vessels.
General signs may include anorexia (loss of appetite), depression, stiffness and reluctance to walk, ataxia (incoordination), coughing and dyspnoea (difficulty breathing). A tick may be found with a careful search.
Subclinical
The thrombocytopaenia persists but the obvious signs abate.
Chronic
The bone marrow which is responsible for producing the leucocytes (white blood cells that fight against infection), erythrocytes (red blood cells that carry oxygen) and thrombocytes (platelets) becomes exhausted as a result of great demands caused by the Erlichiosis leading to reduced cell production. At this point the Ehrlichia is able to do more damage than the body can cope with and the clinical signs of the disease may re-emerge.
Signs may include lethargy, depression anorexia, weight loss, fever, spontaneous bleeding from gums and nose, respiratory distress, edema (fluid swelling) of limbs or scrotum, uveitis and retinal hemorrhage with detachment in the eyes and neurological (nerve related) signs such as ataxia (incoordination) and head tilt. German shepherds and Doberman pinschers have a greater tendency to develop the chronic form of disease.

Diagnosis of Ehrlichia is based on blood tests which show the damage to the blood cells or the presence of antibodies which indicate the body has reacted to the Ehrlichia. It is uncommon to be able to specifically identify the Ehrlichia in the cells

Animals that have minimal changes in their blood cells can be treated at home, but those that have significant alterations will need to remain in hospital to receive intensive treatment. Animals that present in the acute stage have an excellent prognosis (outlook) and the progression to the chronic phase can be avoided. Those with the chronic form may take up to a month to show any response to treatment, and if the bone marrow has been significantly affected then the prognosis is poor.

Tetracycline antibiotics are the preferred treatment, except in pups less than 6 months old, where chloramphenicol is the drug of choice despite its own potential cause bone marrow suppression. Blood transfusions and intravenous fluids can be administered where warranted. The platelet levels need to be monitored every 3 days to ensure they are increasing back to normal levels. Blood testing is repeated after 9 months of treatment to ensure resolution is complete. Where results are still positive then treatment needs to be repeated with further blood testing 6 months later.

Ticks need to be removed from animals and chemical treatments should be used to prevent reinfestation. When removing ticks it is important to wear gloves and ensure the mouth parts are completely removed. Humans are thought to have caught the disease from ticks, although probably not the brown dog tick.