Canine Distemper Virus: Wildlife Conservation Implications

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By Sam Lisak

Baltimore Classification

Group V: (−) sense single-stranded RNA viruse

Higher Order Taxa

Order: Mononegavirales

Family: Paramyxoviridae

Genus: Morbillivirus

Species: Canine Distemper Virus

Description and Significance

Canine distemper virus (CDV) is a viral pathogen that is commonly known for its ability to infect domestic dogs, though it affects many other species. This single-stranded, negative-sense RNA virus belongs to the Paramyxoviridae family and the genus Morbillivirus [1]. CDV is highly contagious, spreading through aerosol droplets and bodily fluids. Generally, the virus initially replicates in the respiratory tract where it enters the blood stream and spreads to lymphoid, nervous, and epithelial tissues [2]. While symptoms depend on the host species as well as the strain and severity of the virus, CDV often causes fever, ocular discharge, lethargy, anorexia, vomiting, diarrhea, seizure, paralysis, and the thickening of feet pads [3]. Although much research on this virus concentrates on its relationship to domestic dogs, CDV affects many carnivore families such as Canidae (domestic and wild canids), Ursidae (bears), Pinnipeds (seals, sea lions, etc.), and Felidae (wild cats), to name a few [4]. Due to the wide range of potential hosts and the easy transmission pathway from domestic dogs to wildlife, CDV poses a significant threat to the conservation efforts of many threatened mammals. This report attempts to summarize current research on CDV as well as provide insight on how the virus affects wildlife, particularly, the conservation of threatened species.

Virion and Genome Structure

Figure 2. Virion and genome structure of Canine Distemper Virus[5].

All Morbilliviruses, including CDV, are virions enveloped by a lipid bilayer containing a single-stranded, negative-sense RNA genome [6]. CDV virus particles typically are between 150-300 nm in diameter [7].Their genomes code for six structural proteins in the following order: N (nucleocapsid), P (phosphoprotein). M (matrix protein). F (fusion protein) (See Figure 2). H (hemagglutinin protein), and L (large protein). They also code for V and C, two non-structural proteins [5]. The P and L proteins are coupled and attached to the N protein, which surrounds the genome to form the nucleocapsid. The P protein serves as the co-factor for the viral RNA-dependent RNA polymerase (L protein) [5]. The two glycoproteins, H and F, are spikes embedded in the lipid bilayer that mediate fusion between other cells. The envelope-associated M protein is evenly arranged underneath the lipid bilayer and regulates the two glycoproteins in addition to linking the nucleoplasmid with these proteins [5].

The CDV genome consists of 15,616 nucleotides and parallels the genomes of other morbilliviruses, particularly that of its closest relative, the measles virus (MV) [8]. This genome begins with the putative regulatory 3' leader (55 nucleotides long) that directly precedes the N gene, which is then followed by the P, M, F, H, and L genes. Between the L gene and the end of the CDV genome (the 5' terminus), lies the putative 5' leader region (38 nucleotides long) [9]. The putative sequences direct the transcription and replication of the genome. Intergenic sequences, located at the 3' and 5' ends of every structural gene segment control transcription termination and reinitiation [10].

Viral Ecology and Pathology

Include some current research in each topic, with at least one figure showing data.

Signs and Symptoms


Prevention and Treatment

Figure 5. Nobivac® DHP, a widely available CDV vaccine [12].

The prevention of CDV, while simple in theory, is almost impossible to successfully implement. Effective vaccines exist and are the only realistic solution for controlling canine distemper in domestic dogs [13] (See Figure 5). While CDV vaccines have greatly decreased the prevalence on canine distemper, the disease still spreads among unvaccinated populations including animal shelters, pet stores, and feral dogs. Additionally, many domestic dogs are suceptible to CDV if their owner forgets or declines to vaccinate their puppies with the required booster shots that are needed until the puppy reaches 16 weeks [14]. Prevention of CDV in captive wild animals can be achieved through careful vaccination, however these vaccines must be proven to be safe for the animals as they can occasionally have adverse effects [13]. However, the widespread vaccination of wild animals is obviously unfeasible, so effective conservation and wildlife management strategies must be implemented to achieve prevention (possible solutions described below).

Despite the widespread prevalence of CDV vaccinations, there are currently no antiviral drugs or specific treatments for canine distemper [15]. Available treatments are symptomatic, aimed at controlling neurological dysfunction, maintaining fluid balance, and defend against secondary bacterial invasions [16]. However, there is hope for an antiviral medication after studies have shown the drugs ribavarin (RBV) and interferon-alpha (IFNα) inhibit the replication of CDV in vitro [15].

Effect on Wildlife Conservation

The ability of CDV to infect all terrestrial carnivore families (Mustelidae, Ursidae, Viverridae, Procyonidae, Felidae, Hyaenidae, and Canidae) allows it to threaten the conservation efforts and long-term survival of many species [17] [18]. Large predators are frequently in danger of extinction due to their reliance on large tracts of habitat, vulnerability to poaching, and frequent conflicts with humans. Exposure to CDV only exacerbates the pressure on these struggling populations of carnivores. Part of what makes CDV so dangerous to wildlife populations is its ability to spread between many species [19]. Domestic dogs are most common reservoir for the transmission of CDV to wildlife populations. However, infected individuals of the same species in addition to other wild carnivores can also spread the virus. As the human population continues to expand, the threat of the transfer of CDV to wildlife populations only grows [20].

Figure 2. .[21].

CDV has repeatedly demonstrated the ability to drive species of already threatened species further towards extinction. A study on a population of Amur tigers (Panthera tigris altaica) in the Sikhote-Alin Biosphere Zapovednik (SABZ) assessed the impact of CDV on this population in addition to modelling how CDV could influence the potential extinction of tiger populations of various sizes. Their model found that the prevalence of CDV could increase the 50-year extinction probability of the tiger population in SABZ by 6.3% to 55.8% [22] (See Figure ). The most important factors determining the model's outcome was the prevalence of CDV in reservoirs (domestic dogs and other wild carnivores) and its rate of effect contact with tigers [22]. Many endangered species only remain in small populations (relative to former levels), making them particularly susceptible to CDV. Given the ability for CDV to jump from domestic dogs to wildlife populations, many studies have focus on monitoring populations of domestic dogs that could potentially come into contact with target species. A recent study examined the ability for CDV transmission from domestic dogs to threaten giant panda (Ailuropoda melanoleuca) populations. Their study population of pandas were found to be extremely susceptible to CDV due to a lack of an antibody for the virus in addition to living in close proximity to unvaccinated domestic dogs that have been exposed to CDV [18].

Figure 2. .[23].

As more and more species are pushed to the brink of extinction, conservationists are increasingly relying on ex situ conservation strategies such as captive breeding programs as last-ditch efforts to save species. Captive breeding programs can be used to establish new populations of endangered species, bolster existing ones, and preserve species' genetic diversity [24]. However, CDV not only impedes in situ conservation efforts described above, but has devastated various captive breeding programs as well. The African wild dog (Lycaon pictus) is a critically endangered species of Canidae native to sub-Saharn Africa. In 2000, a captive breeding program of African wild dogs in Tanzania experienced an outbreak of CDV, killing 49 of 52 animals in only two months [25]. The importance of a successful breeding programs is demonstrated by the rescue of the black-footed ferret (Mustela nigripes) from the brink of extinction. In 1964, scientists were redy to declare this species extinct when a small population was discovered. However, this population continued to decline and, in 1971, scientists started a captive breeding program after capturing individual from this population [26]. However, the majority of these captive individuals were infected with CDV and died out, as did the wild population. Conservationists received a second change in 1981 when another population in Wyoming was discovered. Unfortunately, CDV wiped out most of this population and, in 1986, the last 18 individuals were captured to start a captive breeding program [27]. Scientists were able to prevent the outbreak of CDV in this population with terrific results. While this species is still endangered, it represents one of the greatest conservation success stories. Today, there are ~300 individuals in captive breading programs and hundreds and ~300 individuals in the wild; 4,100 ferrets have been reintroduced to the wild since 1991 [28]. Clearly, it is essential to prevent the spread of CDV to captive breeding programs if they are to successfully aid conservation efforts.

Potential Conservation Solutions

Figure 2. A critically endangered Amur leopard (Panthera pardus orientalis), populations of which have recently been infected by CDV, threatening the survival of this species.[29].


Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2018, Kenyon College.