Hello, my name is***** and I have over 20 years of experience as a veterinarian.
I am sorry to hear that your pup Darla has had an abnormal heat cycle with heavy bleeding, lethargy, poor appetite, dehydration, and heavy salivation.
I am more concerned about her because of her lethargy and dehydration in spite of fluid therapy.
An increased vaginal discharge can indicate endometritis, which is due to a thickened, abnormal uterine lining. This isn't necessarily dangerous for her, but it does indicate that she likely has abnormal fertility because of her thickened uterine lining. But these dogs aren't usually sick, they are otherwise normal with an abnormally heavy vaginal discharge.
Another reason for an increased discharge can be a uterine infection called a pyometra. Pyometras can rupture, causing peritonitis and/or the infection can spread to her other organs leading to abscesses in her kidneys, liver spleen and even her heart valves. The toxic metabolites from the infection can affect her appetite and cause her to drink lots of water as the infection progresses or become seriously dehydrated if they are too nauseous to drink more due to fluids/blood being drawn into the uterus.
Early on the symptoms of an open pyometra and endometritis can be very similar as long as the pyometra is draining. That is because if the infection is draining she may not feel the effects of the bacterial toxins as quickly as if the infection was closed in and the toxin levels build up more quickly in her uterus and bloodstream.
Antibiotics alone do not work to treat a pyometra as they have poor penetration into an infection filled uterus and do not address the pool of infectious material and toxins in her uterus. We sometimes use prostaglandin injections and combination antibiotics in dogs that owners want to breed another time if the dog is feeling relatively well otherwise, but the success rate is variable. And even if it works if she isn't bred successfully on the next heat the chances of the infection returning are very high.
Her low white blood cell count could indicate a viral infection, thus their reasoning for looking for Parvo virus given her extreme nausea too. Most dogs with bacterial infections have elevations in their white blood cell count. But in some dogs with very severe bacterial infections the immune system cannot keep up, all of the white blood cells are drawn into the area of infection (in her case possibly her uterus) and the circulating white blood cell count looks artificially low.
Addison's disease, which is a poorly functioning adrenal gland, can lead to lots of vague symptoms including weakness, dehydration, loss of appetite and sometimes diarrhea and vomiting. Dogs may initially appear fairly normal on examination and on routine blood tests, other then showing signs of dehydration and decreased numbers of white blood cells, so they can be difficult to diagnose.
These dogs cannot handle stress at all because their adrenal gland doesn't produce cortisone when stressed and their electrolytes can be off too if their adrenal gland isn't controlling that normally either. We can see physical collapse in severely affected dogs.
It is more commonly seen in young, female, adult dogs.
Testing is an ACTH response test to check adrenal gland function and checking electrolyte levels.
Treatment is steroid replacement therapy and electrolyte replacement.
Many dogs respond very well to fluid and electrolyte therapy, but will relapse quickly if proper medical treatment doesn't follow.
If you want to read more about Addison's disease here is a link to a webpage with accurate information: http://www.vetmed.wsu.edu/cliented/addisons.aspx
Ideally they should check an ACTH response test, keep her hydrated in the meantime with intravenous fluids, and consider an abdominal ultrasound to further evaluate her uterus.
They need to try and differentiate between Addison's and an early pyometra because treatment is very different. The sooner that she is diagnosed the better as if this is a pyometra the sooner that is addressed the better chance she has of doing well., and if this is Addison's and she isn't treated she can collapse and we could lose her.
Treatment for a pyometra is stabilizing her with intravenous fluids and antibiotics and surgery to remove the infected uterus. The longer that you wait the more opportunity this infection has to spread and the more difficult it will be to save her.
If she seems to feel great otherwise I recommend that you have her seen as soon as possible by her regular veterinarian.
I know that it is frustrating not to have an answer after already running several tests, and to have a dog that feels horrible despite treatment but her veterinarians are doing the best that they can to find and cause that will allow more effective, definitive treatment.
Please let me know if you have any further questions.