Saturday, March 21, 2009

Treating Parvo

Treatment for parvoviral infection centers on support. This means that the clinical problems that come up in the course of the infection are addressed individually with the goal of keeping the patient alive long enough for an immune response to generate. We do not have effective anti-virus anti-biotics and must rely on the patient’s immune system for cure.
There are certain basic treatment principles which can be viewed as “must haves” in addressing the parvo puppy. Beyond these basics are some “added pluses” which may or may not contribute to the chance for survival. In order to achieve the usual survival rate of approximately 75-85%, the basics must be delivered. If an owner is less concerned about expense and simply wants to maximize survival chances, some of the optional treatments may be employed.
“Rolly” Flores - Parvo Survivorjust before discharge from the hospital
FLUID THERAPY: One of the ways parvo can kill is via the metabolic derangements that occur with dehydration. It is crucial to replace the vast fluid losses (from vomiting and diarrhea) with intravenous fluids. Fluids are given as a steady drip rather than simply under the skin so that absorption into the circulation is direct. Potassium is usually added to the fluids in order to maintain electrolyte balance. Dextrose (sugar) is also frequently added as the stress of the disease may lower blood sugar especially in a very small puppy.
ANTIBIOTICS: The second way parvo kills is through bacterial invasion of the circulatory system (“sepsis.”) Since the GI tract is damaged, antibiotics cannot be given orally. They are given either as shots or are added into the IV fluid bag. There are a number of antibiotics which may be selected. Some antibiotics you may see in use include:
*Cefazolin *Baytril *Ampicillin *Gentamycin*Amikacin *Trimethoprim-sulfa *Chloramphenicol
Our hospital tends to prefer Cefazolin as a basic choice. For more information on this drug you may wish to read the Pharmacy Center section on its sister drug: Cephalexin.
CONTROL OF NAUSEA: Patient comfort is a very important part of treatment for any disease but is especially important for parvo treatment as these puppies feel extremely nauseated. Again, the GI tract is too damaged for oral medication so medications are given as injections. There are two popular medications for nausea control:
Metoclopramide: (best given as a continuous drip in the IV fluid set up) If used as separate injections, relief tends to be short lasting and does not provide “around the clock” control. If a continuous drip is used, nausea control lasts as long as the drip is running.
Chlorpromazine: a very strong nausea control medication which lasts 6-8 hours per injection and has the added benefit of a drowsiness side effect (so patients can sleep through most of this uncomfortable time).
Injectable antacids (Tagamet, Zantac, or Pepcid) are often used to prevent ulceration of the esophagus of the esophagus should protracted vomited be a problem.
The following tests are helpful in adjusting parvovirus treatment:
Fecal floatation to rule out worms/internal parasites
The last thing these patients need is a parasite burden contributing to their nausea and diarrhea.
White blood cell counts/complete blood counts
One of the first acts of the parvovirus is to shut down the bone marrow production of immunologic cells (the white blood cells). White blood cell counts are often monitored as the infection is followed.
Urine specific gravity/Azosticks
In order to assess the effectiveness of the fluid therapy, some objective evaluation of dehydration is useful. If adequate IV fluids have been provided then the urine produced will be dilute (as measured by “specific gravity”) and azosticks measures of protein metabolites (which build up in the blood stream) should be at normal levels.
Abdominal Palpation
Abnormal motility of the intestines occurs with this infection. Sometimes an area of intestine actually “telescopes” inside an adjacent area in a process called “intussusception.” This is a disastrous occurrence as intussusception can only be treated surgically and parvo puppies are in no shape for surgery. Euthanasia is usually elected in this event.
Total blood protein
Protein depletion is common when there is heavy diarrhea. If blood proteins drop too low, special IV fluids or even plasma transfusions are needed to prevent massive life-threatening edema.
CEFOXITIN (A SPECIAL ANTIBIOTIC) The best antibiotic coverage controls both gram negative and gram positive organisms, both aerobic and anaerobic organisms and does so with minimal side effects. The use of Cefoxitin (brand name Mefoxitin) does an excellent job of covering for the organisms of concern without the kidney side effects of gentamycin or amikacin and without the cartilage side effects of Baytril. Cefoxitin is especially expensive and is frequently reserved for the sickest puppies.
ONDANSETRON (BRAND NAME ZOFRAN) This medication is an especially strong anti-nauseal medication which is useful if the more common medications have failed. This medication is commonly used to control the extreme nausea experienced by people on cancer chemotherapy. While it is highly effective for parvo puppies, it is also very expensive.
SEPTI-SERUM-This product represents anti-serum (antibodies extracted from horses) which binds the toxins of any invading GI tract bacteria. The use of this product is controversial though the veterinary teaching hospital at Auburn University uses it commonly. It is usually given only one time as the equine origin of the product has potential for serious immunological reactions.
PLASMA TRANSFUSIONS In a similar attempt to deliver anti-bodies to the parvo puppy, plasma from a donor dog who has survived parvo is sometimes used. The canine origin of such products reduces the potential for immune reactions but such plasma is not typically available commercially.
ANTI-INFLAMMATORY DRUGS- There have been many studies indicating the benefits of single doses of these medications in the prevention of septic shock. Repeated doses may cause further GI ulceration (which is obviously something a parvo puppy has enough of). Our hospital favors Flunixin meglumine (brand name banamine) for this use.
NEUPOGEN “Neupogen” is the brand name of a genetically engineered hormone called “granulocyte colony stimulating factor.” This hormone is responsible for stimulating the bone marrow to produce white blood cells and its administration easily overcomes the bone marrow suppression caused by the parvovirus. A recent study did not find increased survival with the addition of this product to the parvo regimen; however, in sicker puppies it may make a significant difference. It is very expensive usually adding $100-$200 to the basic treatment cost.
Home treatment for parvo infection is a bad idea when compared to hospitalization and intensive care. Mortality rises substantially and the heavy diarrhea and vomiting lead to heavy viral contamination in the home. Still, if financial concerns preclude hospitalization, home care may be the puppy’s only chance. Fluids will have to be given under the skin at home as will injectable medicines.