Live Canine Distemper Virus Research Articles

Prevalence of Neutralizing Antibodies to Canine Distemper Virus and Response to Vaccination in Client-Owned Adult Healthy Dogs.

Re-vaccinations against canine distemper virus (CDV) are commonly performed in 3-year intervals. The study’s aims were to determine anti-CDV antibodies in healthy adult dogs within 28 days of vaccination against CDV, and to evaluate factors associated with the presence of pre-vaccination antibodies and with the antibody response to vaccination. Ninety-seven dogs, not vaccinated within 1 year before enrollment, were vaccinated with a modified live CDV vaccine. A measurement of the antibodies was performed before vaccination (day 0), on day 7, and 28 after the vaccination by virus neutralization. A response to vaccination was defined as a ≥4-fold titer increase by day 28. Fisher’s exact test was used to determine factors associated with a lack of antibodies and vaccination response. In total, 94.8% of the dogs (92/97; CI 95%: 88.2–98.1) had antibodies (≥10) prior to vaccination. A response to vaccination was not observed in any dog. Five dogs were considered humoral non-responders; these dogs neither had detectable antibodies before, nor developed antibodies after vaccination. Young age (<2 years) was significantly associated with a lack of pre-vaccination antibodies (p = 0.018; OR: 26.825; 95% CI: 1.216–1763.417). In conclusion, necessity of re-vaccination in adult healthy dogs should be debated and regular vaccinations should be replaced by antibody detection.

MODIFIED LIVE DISTEMPER VACCINES CARRY LOW MORTALITY RISK FOR CAPTIVE AFRICAN WILD DOGS, LYCAON PICTUS

Recently, canine distemper virus (CDV) has been linked to population declines in the endangered African wild dog (Lycaon pictus). As CDV appears able to persist in wildlife, threats to free-ranging wild dogs cannot be eliminated by vaccinating domestic dogs. Conservation managers may therefore consider CDV vaccination of wild dogs in highly threatened populations. For use in field conservation, the ideal CDV vaccine would be safe, immunogenic, and readily available in Africa. The CDV vaccine type most commonly used for domestic dogs (modified live vaccine) is available in Africa, and apparently immunogenic in wild dogs, but has been linked to fatal vaccine-induced distemper in captive wild dogs. However, alternatives are either ineffective (inactivated vaccine) or difficult to obtain in Africa (recombinant vaccine). Data from a questionnaire survey of zoo vaccination practices were therefore combined with studbook tracing to assess the safety of modified live CDV vaccine in captive African wild dogs. Among 135 wild dog pups given modified live CDV vaccine for the first time, there was a single, unconfirmed, case of potential vaccine-induced distemper. Pups given modified live vaccine survived better than those given inactivated vaccine or no vaccine. Although studbook tracing revealed higher overall pup survival at zoos which responded to the questionnaire than at zoos which did not, tracing of all pups born during a 20-yr period that lived long enough to be vaccinated (n = 698 pups in 155 litters) revealed no mortality events consistent with vaccine-induced distemper. Modified live CDV vaccine thus appears to carry low mortality risks for African wild dog pups in captivity, and may warrant trials in free-ranging populations.

Use of serologic tests to predict resistance to Canine distemper virus–induced disease in vaccinated dogs

The objective of the current study was to determine whether detection of Canine distemper virus (CDV)-specific serum antibodies correlates with resistance to challenge with virulent virus. Virus neutralization (VN) assay results were compared with resistance to viral challenge in 2 unvaccinated Beagle puppies, 9 unvaccinated Beagle dogs (4.4-7.2 years of age), and 9 vaccinated Beagle dogs (3.7-4.7 years of age). Eight of 9 (89%) unvaccinated adult dogs exhibited clinical signs after virus challenge, and 1 (13%) dog died. As compared to adult dogs, the 2 unvaccinated puppies developed more severe clinical signs and either died or were euthanized after challenge. In contrast, no clinical signs were detected after challenge of the 9 adult vaccinated dogs with post-vaccination intervals of up to 4.4 years. In vaccinated dogs, the positive and negative predictive values of VN assay results for resistance to challenge were 100% and 0%, respectively. Results indicate that dogs vaccinated with modified live CDV can be protected from challenge for ≤4.4 years postvaccination and that detection of virus-specific antibodies is predictive of whether dogs are resistant to challenge with virulent virus. Results also indicate that CDV infection in unvaccinated dogs results in age-dependent morbidity and mortality. Knowledge of age-dependent morbidity and mortality, duration of vaccine-induced immunity, and the positive and negative predictive values of detection of virus-specific serum antibodies are useful in development of rational booster vaccination intervals for the prevention of CDV-mediated disease in adult dogs.

Humoral and cell-mediated immune responses in DNA immunized mink challenged with wild-type canine distemper virus

The aim of the study was to investigate the different phases of the immune response after DNA immunization with the hemagglutinin and nucleoprotein genes from canine distemper virus (CDV). Although attenuated live CDV vaccines have effectively reduced the incidence of disease, canine distemper is still a problem worldwide. The broad host range of CDV creates a constant viral reservoir among wildlife animals. Our results demonstrated early humoral and cell-mediated immune responses (IFN-gamma) in DNA vaccinated mink compared to mock-vaccinated mink after challenge with a Danish wild-type CDV. The DNA vaccine-induced immunity protected the natural host against disease development.

SEROSURVEY OF EX SITU GIANT PANDAS (AILUROPODA MELANOLEUCA) AND RED PANDAS (AILURUS FULGENS) IN CHINA WITH IMPLICATIONS FOR SPECIES CONSERVATION

Conservation strategies for the giant panda (Ailuropoda melanoleuca) include the development of a self-sustaining ex situ population. This study examined the potential significance of infectious pathogens in giant pandas ex situ. Serologic antibody titers against canine distemper virus (CDV), canine parvovirus (CPV), canine adenovirus (CAV), canine coronavirus (CCV), canine herpesvirus, canine parainfluenza virus (CPIV), Toxoplasma gondii, Neospora caninum, and Leptospira interrogans were measured in 44 samples taken from 19 giant pandas between 1998 and 2003 at the Chengdu Research Base of Giant Panda Breeding in Sichuan, China. Seroassays also included samples obtained in 2003 from eight red pandas (Ailurus fulgens) housed at the same institution. All individuals had been vaccinated with a Chinese canine vaccine that included modified live CDV, CPV, CAV, CCV, and CPIV. Positive antibody titers were found only against CDV, CPV, and T. gondii. Sera were negative for antibodies against the other six pathogens. Results indicate that the quality of the vaccine may not be reliable and that it should not be considered protective or safe in giant pandas and red pandas. Positive antibody titers against T. gondii were found in seven of the 19 giant pandas. The clinical, subclinical, or epidemiologic significance of infection with these pathogens via natural exposure or from modified live vaccines in giant pandas is unknown. Research in this area is imperative to sustaining a viable population of giant pandas and other endangered species.

SEROLOGIC RESPONSE TO A CANARYPOX-VECTORED CANINE DISTEMPER VIRUS VACCINE IN THE GIANT PANDA (AILUROPODA MELANOLEUCA)

The giant panda (Ailuropoda melanoleuca) is known to be susceptible to natural infection with canine distemper virus (CDV). Vaccination of giant pandas with conventional modified live CDV vaccines has been avoided due to the numerous carnivore species known to have become infected with CDV after vaccination. Serum-neutralizing antibodies to CDV were measured after s.c. and i.m. annual vaccination with a canarypox-vectored recombinant CDV vaccine in an adult male and female giant panda over the period of 2 yr. The vaccine proved to be safe, and serum-neutralizing antibody titers interpreted as protective against CDV disease were measured in each animal.

Some experiments and field observations of distemper in mink and ferrets

This chapter describes some observations on the occurrence of canine distemper (CD) on mink farms and experimental trials using mink and ferrets. Ferrets—because of their high susceptibility to canine distemper virus (CDV)—show an invariably fatal course, which makes them the most satisfactory animal for conducting many distemper experiments. Vaccination is the only suitable means for the control of mink and ferret distemper. Attenuated live CDV vaccines produce a more dependable, longer lasting immunity and have replaced inactivated vaccines for ranch-raised mink and pet ferrets. Present-day distemper vaccines for mink are inexpensive and effectively immunize susceptible mink, and they can be combined with other vaccines to protect against mink virus enteritis, botulism, and Pseudomonas infections. In the case of dogs, foxes, mink, and ferrets and perhaps all other Mustelidae, Canidae, and Procyonidae, maternal antibody is a double-edged sword protecting young animals from distemper and conversely blocking early chicken embryo propagated (CEP) vaccination.

Abundant expression of viral nucleoprotein mRNA and restricted translation of the corresponding viral protein in inclusion body polioencephalitis of canine distemper

Brain and other tissues of three dogs aged 4-21 months with inclusion body polioencephalitis caused by canine distemper virus (CDV) were examined for CDV nucleoprotein (N) antigen and mRNA distribution. Two animals (nos 3 and 1) had suddenly shown central nervous system (CNS) signs 4 days and 5 months, respectively, after vaccination with a modified live CDV vaccine; animal no. 2 had shown similar signs 4 weeks after vaccination with an unknown product. Lesions in the CNS, which were restricted to the grey matter, occurred most frequently in the diencephalon, mesencephalon, medulla oblongata and, in one animal, in the cerebral cortex. Changes were characterized by mild to moderate perivascular lymphohistiocytic cuffs, loss of neurons, neuronal necrosis, glial nodules, and oedema. Intranuclear and cytoplasmic inclusion bodies, especially prominent in neurons, were observed. By in-situ hybridization, CDV N mRNA expression was confirmed with a non-radioactively labelled N-specific mRNA probe. The corresponding RNA translation product was detected immunohistochemically with a proteinspecific monoclonal antibody. Viral antigen and mRNA were observed in the same cell types and brain compartments. However, the number of cells expressing N mRNA exceeded the number of cells containing viral antigen greatly in two animals and slightly in one. Some areas with abundant viral mRNA expression were almost completely devoid of viral antigen. mRNA and the corresponding translation product were demonstrated in neurons and less frequently in astrocytes, but not in perivascular inflammatory cells. It would appear that distemper inclusion-body polioencephalitis may be due to a non-productive CDV infection of neurons, characterized by abundant expression of CDV N mRNA and reduced translation of the corresponding viral protein. These findings suggest that in distemper the pathogenesis of grey-matter lesions differs substantially from that of white-matter lesions, which constitute the most common manifestation of distemper encephalitis.

Measles virus and inactivated canine distemper virus induce incomplete immunity to canine distemper.

Pairs of specific pathogen free dogs were immunized with two injections of heat inactivated canine distemper virus (CDV) or one injection of a live CDV or live measles virus (MV) vaccine. Three unimmunized dogs were used as controls. All 9 dogs were challenged with virulent CDV (Snyder Hill strain). The three unimmunized dogs developed severe signs of disease with a lethal infection in one. The two dogs immunized with live CDV vaccine developed a strong humoral as well as cellular immune response after immunization and were protected against virus replication. Animals immunized with either inactivated CDV or modified live MV failed to develop a measurable cellular immune response after immunization and had a comparatively weak humoral immune response to distemper antigens. They showed mild signs of infection after challenge and responded with strong anamnestic cellular and humoral immunity. The measles vaccine immunized dogs had a moderate serum titer of measles hemolysin-inhibiting antibodies which, after exposure to distemper virus, was boosted to high levels. It is proposed that this response plays a role in the mitigation of the virulent distemper infection in these animals.