Canine Distemper Is Alive and Well and More Dogs Are Dead

According to the third edition of Veterinary Virology (1999), “Canine distemper is the most important viral disease of dogs, producing high morbidity and mortality in unvaccinated populations worldwide.” However, for many years, perhaps 20 or 30, canine distemper (CD) has not been the significant clinical problem it once was in the United States presumably because of our high rate of vaccination. That is, until recently. Popular literature and even professional veterinary publications are replete with the idea that we are vaccinating dogs too much. Now it appears that CD may be making a comeback. Do we have too many unvaccinated dogs and/or is a new strain able to overcome protection of current vaccines?

Nikki Proutsos, Executive Director of Chicago Animal Care and Control, has recently stated that there have been over eighty confirmed cases of CD in the Chicago area since May of this year against no confirmed cases in 2003. The situation has prompted Chicago Animal Care and Control to suspend their dog adoption program. This apparent outbreak is not limited to Chicago, but seems to be occurring in multiple states east of the Mississippi river especially in kennels, pet stores and animal shelters. Diagnosis of CD can be a clinical challenge but laboratory confirmation is not difficult with good reagents.

In late August of this year blood samples and organs of five dogs were submitted to American BioResearch by Dr. Page for conformation of CD. Tissues were cultured for the presence of virus and impression smears of brain and lung tissues were examined by direct immunofluorescence (DFA). Sera were titered for CD virus (CDV) specific IgG and IgM by IFA as previously described.(1) Samples were sent to VMRD, Inc. for DFA of blood and cryostat sections of lung and brain tissues.

Reagents used: CDV FA substrate slide (VMRD 210-88-12-CDV), CDV IgG positive control (VMRD 211-P-CDV-G), CDV IgM positive control (211-P-CDV-M), anti-canine IgG FITC conjugate (VMRD 035-10), serum diluting buffer (VMRD 210-93-SB), rinse buffer (VMRD 210-90-RB), mounting fluid (210-92-MF), CDV direct FA conjugate/polyclonal (VMRD 210-02-CDV), and CDV control slide (VMRD 210-88-2-CDV).

Table 1, Clinical Data, provides details about the clinical presentation including ages and breeds of the dogs. Table 2, Diagnostic findings, details the results of the diagnostic work performed by ABR and VMRD. Figures 1-5 are digital photomicrographs of DFA results on cryostat sections. 

Clinical Data

Case	Breed	Age	Clinical Presentation	Disposition
1	Labrador Retriever	7-8 weeks	Diarrhea intussusception	Died
2	Sheltie	7-8 weeks	Peripheral neuritis and paralysis, pneumonia	Euthanized
3	Cocker Spaniel	7-8 weeks	CNS signs and pneumonia	Euthanized
4	Sheltie	7-8 weeks	CNS signs including seizures, diarrhea, matted eyes/nose, (classic)	Died
5	Miniature Poodle	Adult, 4 years	Staggering gait, poor balance, apparently blind	Euthanized

Diagnostic Findings

Dog	Serology Titer	Blood DFA	Lung Impression  DFA	Brain Impression  DFA	Lung Cryosection DFA	Brain Cryosection  DFA	Virus Isolation
IgG	IgM	Lung	Trachea	Brain
1	<50	<10	-	NT (2)	NT	NT	NT	NT	NT	NT
2	<50	50	2+	4+ (3)	3+	NT	NT	NT	NT	NT
3	<50	100	1+	4+	2+	3-4+	NT	+	+	NT
4	<50	50	3+	4+	4+	4+	4+	+	+	+
5	1250 (1)	100	-	-	4+	-	4+	-	NT	+
1 Inclusions only
2 Not tested
3 Refers to numbers of positive cells

Figure 1. CDV antigen positive cells in bronchiole 400X)

Figure 2. Heavy concentration of CDV antigen in brain and single large inclusion (400X)

Figure 3. Single neuron showing CDV cytoplasmic inclusions (400X)

Figure 4. CDV antigen around vessel in brain (400X)

Figure 5. CDV antigen inclusion in peripheral white blood cells (higher magnification than other photographs).

References 

1. Black, John W., “Single Serum-Sample Diagnosis of Canine Viral Diseases,” VMRD, Inc. Newsletter, Volume 1, No. 2, October 1994.