Canine Parvovirus, which is commonly referred to as “parvo”, is a small, nonenveloped, single-stranded DNA virus that, when contracted, results in a lethal infection to unvaccinated and immunocompromised canines. The virus was first discovered in 1978 and named Parvovirus Type 2 (CPV-2) after its predecessor (CPV-1), which was asymptomatic in most patients (Mochizuki, 2002). This marked the second canine parvovirus discovery. CPV-2 at this time was determined to require a host cell; such as intestinal crypt epithelial cells, precursor cells in the bone marrow, and myocardiocytes in the heart. Though this virus is most commonly found in domesticated canines, it is compatible with wild canines such as wolves, foxes, hyenas, coyotes, and others (Thomas et al., 1984).
Since the discovery of vaccines in the 1970s, Parvovirus has mutated into three strains: CPV-2a, CPV-2b and CPV-2c, each with slightly different symptoms and treatment needs. Vaccines today have improved to prevent illness caused by all three strains of the virus, though breakouts still occur frequently throughout the world (vet.cornell.edu, 2019). The two primary reasons that breakouts still occur, and the virus has not been eradicated, are the failure of owners to vaccinate appropriately, and the rapid mutation rate of the virus. To prevent canines from contracting the virus, professionals recommend that the canine should receive three sets of Parvo vaccines between 6 and 16 weeks with 3-4 weeks between each.
CPV-2 has the ability to live in the environment for over a year in places that are not frequently sterilized and have a large canine population available. Places may include; Veterinary hospitals, pet shops, boarding kennels and commercial breeding establishments (Jacob, 1980). Parvovirus is spread through direct exposure to fecal matter of an infected individual. Through studying this virus, scientists are able to determine how CPV-2 mutates and spreads as well as develop better prevention and treatment methods to improve canine health and lower the overall mortality rates of CPV-2.
Clinical Analysis and Treatment
Parvovirus can affect canines of any breed, age and sex, though puppies between six weeks and six months are most susceptible, due to compromised immune systems (Houston et al., 1996). Neonates are protected against infection by maternally derived antibodies in the mother's breast milk. This is only beneficial to the neonate if the mother possesses the antibodies necessary against the virus at the time of birth. Some studies suggest that due to genetic variation in canines, some dog species and/or breeds may be more or less susceptible to contracting the virus when they come in contact with it (Li et al, 2017). Domestic canine breeds at the most risk, due to lack of antibodies, include: Rottweiler, Doberman Pinscher, American Pit Bull Terrier, Labrador Retriever and the German Shepherd Dogs (Glickman et al., 1985).
The incubation period of CPV-2 is between three to seven days with common symptoms including: vomiting, loss of appetite, lethargy, depression, fever and diarrhea. The diarrhea often has a very strong odor and may contain mucus and/or blood (Nelson et al., 1979). Common diagnosis is done in the standard veterinary clinic with the use of a stool sample and a Snap test. Some initial tests may result in a false negative result and require additional antibody testing of the patient’s plasma or serum. Alternative diagnostics include; electron microscopy to detect CPV virus, viral isolation, fecal hemagglutination, latex agglutination, counter immunoelectrophoresis, immunochromatography, and polymerase chain reaction (PCR).
Treatment includes supportive care due to no agent-specific treatment existing. Patients with mild symptoms may be recommended for outpatient treatment, though due to worsening symptoms and difficult oral treatment at home, the majority of patients are hospitalized for an average of 2-7 days. Supportive care includes Crystalloid treatment, correction of hypoglycemia and electrolyte disturbances, antiemetics, analgesics, enteral nutritional support and anthelmintics. Mortality rates without treatment remain at 90% but are decreased to 5-20% with aggressive veterinary treatment (Butler et al, 2018). Modern day Parvo research focuses strongly on improving treatment options, preventing virus spread, advancing vaccine technology and reducing the virus’ mortality rate (Ward, E., n.d).
Fresh frozen plasma has been recorded to provide parvovirus positive patients with benefits such as supplying immunoglobulin and serum protease inhibitors that have the potential to neutralize circulating antigens and aid in minimizing the systemic inflammatory response (Bragg, 2012). Additionally, there is a controversial discussion within veterinary medicine regarding fresh frozen plasma having the ability to promote passive immunity when given from a recovered parvo patient and given to an infected one.
Origin of the Virus
Canine Parvovirus was first visually observed in the early 1970s as a small, round, non-enveloped virus, was observed by electron microscopy in stool specimens and in tissues of affected animals (Kelly, 1978). Due to symptoms of Canine Parvovirus closely mimicking those of Feline panleukopenia virus (FPV), some studies have found genetic mutations that theorize that CPV arose as a mutated version of FPV. Genetic coding reveals that more than 98% of the genetic DNA sequence in CPV and FPV are the same. Differences occur at six coding nucleotides within the VP2 gene at positions 3025, 3065, 3094, 3753, 4477 and 4498. These differences have resulted in CPV-2 being able to acquire canine host range, but lost the ability to replicate in feline host (Nandi et al. 2010) Similar studies have determined that mutations in the CPV-2 virus not only vary between continents, but also within regions of any given country.
Studying the Virus
The leading factor contributing to the mutation and spread of CPV is due to its ability to replicate with the use of a host cell’s DNA polymerase (Cotmore and Tattersall, 1987). Their ability to mass replicate makes the virus highly contagious while the low error rates of the polymerase make mutations rare. It is inferred that the rate of variation is between 1X10-4 and 4X10-4 changes/nucleotides/year. Current studies report that there are only three known strains of CPV-2 worldwide; CPV-2a, CPV-2b and CPV-2c. Each one varied by the others by only five-six amino acids. None of these mutations in the virus have reported a change in virus symptoms or response to aggressive treatment. (Parrish, 1991).
DNA sequencing reveals that the CPV-2 strains throughout Mexico originate from two possible introduction events while all CPV-2 strains in Europe originate from a single event. (Faz M. et al, 2019) In locations of the world such as Nigeria, with a large population of wild canines in close living conditions such as city limits, Parvovirus is known to mutate at increased rates due to the abundance of hosts (Apaa, 2016). Parvovirus has also been found to migrate locations by traveling on various fly species and eggs. Data suggests that veterinary facilities without a private clientele result in higher fly populations that are PCR positive for CPV viruses (Bagshaw et al., 2014).
Global trends that contribute to the spread and manifestations of Parvovirus include; Number of vaccines, age of the patient, breed, sex and location. Historical findings suggest that the patients most likely to contract the virus are intact males who are between three weeks and six months, have no vaccines, and are one of the following breeds; Rottweiler, Doberman Pinscher, American Pit Bull Terrier, Labrador Retriever or German Shepherd (Glickman et al., 1985). Findings also suggest that patients that undergo hospitalization stay an average of 2-7 days in hospital before returning home. There are to date no correlation between geological location and an increased risk of domestic canines contracting the virus. It is suggested that countries with a large wild dog population may be at greater risk, but there is no conclusive data of this trend. There is not enough research regarding fresh frozen plasma transfusion in parvo patients to establish a trend.
Materials and Methods
Data for analysis was collected using Ezyvet software for Salt Lake City emergency Veterinary center; Advanced Veterinary Care. A total of 991 Patients were extracted from 2017-2019 due to a billing trigger within the system that indicated an Idexx Parvo Snap Test had been run for that patient. From the total data count, 31 patients were eliminated from the study due to their feline status and inability to contract CPV. The remaining 955 patient records were evaluated for parvo positive or negative status. Only 192 samples were marked as Parvo Positive and data was extracted for analysis. Parameters for study from each patient record include; age, breed, number of reported vaccines, Treatment type (defined as Outpatient, Euthasasia, Hospitalization and None) and If the patient survived with treatment. Additional data retrieved only for patients that were hospitalized includes; Days spent in hospital and if the patient received a plasma transfusion in hospital. Names of patients were excluded from the data to protect owner and patient privacy.
Figure 1. More than half of all patients who were tested positive for parvovirus had between zero (31%) and one set of vaccines (29%). Approximately 18 patients (9%) had two sets of parvo vaccines and 21 patients ( 11%) had all three sets of parvo vaccines. About 39 patients (20%) had an unknown vaccine history. Figure 2. Parvo Positive Patients were ordered by age in months with youngest on the left and oldest on the right. The majority of patients were between the ages of one and eight months with mode value of three months. The oldest patient (data point excluded from graph) was 89 months (7 years 4 months). The youngest patient to contract parvo virus was 3 weeks old. Figure 3. Approximately 82 (42%) of all patients were treated using outpatient methods. Following this is 74 (36%) who were hospitalized, 25 (13%) who were euthanized without treatment and 11 (6%) who were taken home without any form of treatment. Figure 4. Over the past three years 42% of all Parvo positive patients were seen in 2018. About 36% were seen in 2017 and the remaining 22% were seen in 2019. Figure 5. A total of 102 patients (53%) who were parvo positive were intact males, 75 patients (39%) were intact females, 11 (6%) were neutered males and the remaining 4 (2%) were spayed females. Figure 6. Describes the most common breed to be diagnosed with parvo is the Labrador Retriever. This is followed by the Australian cattle dog mix and the German Shepherd. Finally; The American Pitbull Terrier, the Border Collie, The Labrador mix and the Pug are all tied as the third most common breed. Figure 7. Patients treated in hospital stayed between 2 and 8 days with an average of 3 days. Figure 8. Out of the total 74 parvo patients that were hospitalized for aggressive treatment, eight of them received a fresh frozen plasma transfusion. Figure 9. A total of 50% of Parvo patients treated in hospital and received a plasma transfusion survived.
Figure 1. Total of 192 patients who were parvovirus positive at the Salt Lake City Clinic, sorted based on their reported vaccine history.
Figure 2: 192 patients who were parvovirus positive at the Salt Lake City Clinic, sorted by their age in months. Data points excluded for formatting include one patient age 3 weeks and one patient age 89 months (7 years 4 months).
Figure 3: 192 patients who were parvovirus positive at the Salt Lake City Clinic, sorted by their treatment type chosen by owners. Catagories include; euthanasia, hospitalization, outpatient and none if owners took home without care.
Figure 4: Total number of parvovirus positive cased by year at the Salt Lake City Clinic.
Figure 5: 192 patients who were parvovirus positive at the Salt Lake City Clinic, sorted by their sex and spay/neuter status.
Figure 6: Breeds at the Salt Lake City Clinic most commonly diagnosed with parvovirus. All breeds with less than three patients were eliminated from the data set.
Figure 7: All treated parvo virus positive patients in Salt Lake City hospital sorted based on days stayed in hospital. (Total of 74)
Figure 8: All treated parvo virus positive patients in Salt Lake City hospital and status regarding if they received a plasma transfusion.
Figure 9: The total count of parvo patients in Salt Lake City hospital and their survival status with aggressive treatment.
Figure 10: The survival status of all 8 patients who received a plasma transfusion at a Salt Lake City hospital .
Parvovirus is a lethal infection that affects young and unvaccinated canines. Dogs receive this infection through direct exposure to an infected canine feces and symptoms of vomiting, diarrhea, loss of appetite and lethargy start between three and seven days. Following exposure, aggressive treatments improve the mortality rate from 90% to 5-20% (Butler et al., 2018). Data collected from Advance Veterinary Care (Figure 9) reveals a mortality rate of 8% for parvo positive patients who undergo aggressive treatment in hospital.
The primary way to prevent canine parvovirus is through three sets of vaccines that puppies receive between the ages of 6 and 16 weeks. Each vaccine should be given between 3 and 4 weeks apart. Patients must receive all three sets of vaccines to ensure appropriate protection against the virus. Missed vaccines at any set results in an increased risk. Figure 1 reveals that 60% of patients observed had between no vaccines and one set of vaccines. Approximately 20% owners were unsure of their pets vaccine history and were categorized as Not applicable (NA) in the data set.
Puppies are most susceptible to contract CPV-2 between the ages of 6 weeks and 6 months (Gairu Li et al, 2017). Figure 2 reveals that of the patients observed at Advance Veterinary Care, 46% of Parvo positive patients were between the ages of 3 and 4 months. A total of 57 patients (30%) were older than 6 months and outside the global range as being likely to contract parvovirus. Hospitalization is recommended for treatment in the majority of cases due to worsening symptoms and difficult oral treatment at home, the majority of patients are hospitalized for an average of 2-7 days (Butler J. et al, 2018) or 3 and 6 days (Giorgio Q. Pereira et al, 2017). In Figure 3 A total of 13% of pet owners who recieved a parvovirus diagnosis oped for humane euthanasia. Following 42% requested for outpatient treatment, 38% hospitalized and 7% refused treatment of any kind. The resistance to hospitalize as recommended in many cases was observed to correlate strongly with the owners lack of finances. Figure 7 reveals a total of 73 patients were hospitalized for aggressive treatment, 53% of those patients were hospitalized between 1 and 3 days and the remaining 47% stayed between 4 and 8 days. Overall, patients stayed for a mean of 3 days in hospital before continuing with oral treatment at home.
Fresh frozen plasma has been recorded to provide parvovirus positive patients with immunoglobulin and serum protease inhibitors that have the potential to neutralize circulating antigens and aid in minimizing the systemic inflammatory response. Of the 73 patients hospitalized for aggressive treatment only 8 received a fresh frozen plasma transfusion. (Figure 8) This is a controversial form of treatment within veterinary medicine due to inadequate research done and data collected. Of the 8 patients who received a fresh frozen plasma transfusion only 50% survived. (Figure 9)
Additional findings through data collection reveal that The year 2018 contained the most Parvovirus Positive cases with a total of 81 cases, followed by 2017 with 64 and the year 2019 had the least with 47 Cases. (Figure 4). Some studies loosely correlate that intact males are more likely to contract the virus than intact females, spayed females and neutered males. This is especially true in older age groups. (Taguchi, M, 2011). From the data collected; 53% were intact males, 39% were intact females, 12% were neutered males and 4 % were spayed females. (Figure 5)
Data collected from Advanced Veterinary Care in Salt Lake City, UT agree that intact males between one and three months that have no vaccines are the most likely to contract the virus. The data also agreed that the American Pit Bull Terrier, Labrador Retriever and German Shepherd were breeds more likely to contract parvovirus. Data excluded the breeds; Rottweiler and Doberman Pinscher and instead included the American Cattle Dog mix, Border collie mix, Labrador mix and Pug (Figure 6).
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