Canine Distemper Virus: Understanding the Threat

Section 1: Canine Distemper Pathogen

The causative agent of canine distemper is the Canine Distemper Virus (CDV), which belongs to the Paramyxoviridae family and the Morbillivirus genus. CDV is highly susceptible to heat and dryness, and can be inactivated within 1030 minutes at 56°C, or killed by direct sunlight exposure for 14 hours. However, at lower temperatures, its survival time is significantly extended; for instance, under conditions of 24°C, CDV can remain viable and infectious for several weeks, and can be preserved for years when freezedried. This is why canine distemper is more prevalent during the cold seasons of winter and spring, as well as autumn and winter.

Aldehydes, alcohol, coal tar soaps, and 3% sodium hydroxide can kill CDV, making them suitable disinfectants for the disease. CDV is also sensitive to ultraviolet light. The virus can replicate and grow in primary or cell culture lines from humans, dogs, monkeys, and chickens.

Section 2: Canine Distemper Epidemiology

Canine distemper can occur yearround, but it is most prevalent during the transition periods between autumn and winter, as well as winter and spring. The virus can infect dogs of all ages and breeds, with puppies under one year old being the most severely affected. Other animals, such as wolves, foxes, and minks, can also be infected and become ill.

Infected and carrier dogs are the primary sources of transmission, releasing the virus through saliva, nasal mucus, tears, exhaled air, and urine. Particularly, recovered dogs can shed the virus for an extended period. The virus contaminates the environment and various items, leading to infection in healthy dogs. Transmission primarily occurs through airborne particles and direct contact between dogs, as well as through contaminated environments. The virus initially enters through the respiratory tract, with gastrointestinal infection being a secondary route. As a result, even with proper disinfection and isolation, susceptible dogs in the same environment may still contract the disease.

Section 3: Canine Distemper Clinical Symptoms

The incubation period for canine distemper typically ranges from 3 to 9 days. Initially, symptoms are often subtle, going unnoticed for several days after infection. The severity and variety of symptoms depend on the virulence of the CDV, the presence of secondary bacterial infections, the age and immune status of the dog, and climatic conditions. Vaccinated dogs may only exhibit symptoms like fever, upper respiratory infection, and loss of appetite. Severe cases are usually seen in puppies that have failed to develop immunity or those that have not been vaccinated, and are less common in adult dogs. The most characteristic symptoms include biphasic fever, respiratory inflammation, pneumonia, gastroenteritis, and neurological signs.

Initially, dogs may experience a rise in body temperature, usually between 39°C and 41°C, lasting 13 days before gradually subsiding. The dog may appear to improve and eat, but a few days later, the temperature may rise again, lasting for one to several weeks, with the condition worsening. There may be a decrease or loss of appetite, vomiting, redness of the mucous membranes in the eyes and nose, and the discharge may change from serous to mucopurulent. Auscultation or Xray examination may reveal upper respiratory infection and pneumonia. Dogs may breathe rapidly and have an increased respiratory rate. Some dogs may suffer from severe diarrhea, occasionally with blood in the stool, and may exhibit tenesmus.

Most dogs either die or recover after experiencing respiratory and gastrointestinal symptoms, but some cases may develop neurological symptoms. Some dogs may present with neurological signs from the onset, often characterized by lethargy, muscle spasms, or generalized seizures, as well as ataxia and circling. In severe cases, dogs may experience convulsions or seizures, leading to coma and death. Some dogs may have permanent sequelae after recovery, such as muscle spasms, particularly in the facial and leg muscles. Some may experience localized paralysis, and in some cases, hyperkeratosis of the paw pads and vesicles may appear in areas with sparse fur on the lower abdomen. The disease course can last from 10 days to several weeks or even months.

It has been observed that if a bitch becomes infected with CDV during pregnancy, she may experience abortion, stillbirths, and a decrease in the survival rate of puppies. Puppies infected in utero may exhibit neurological symptoms at around 5 to 6 weeks of age.

Section 4: Canine Distemper Diagnosis

Due to the diverse clinical symptoms and the frequent occurrence of secondary bacterial infections, or coinfections with canine parvovirus or canine adenovirus, diagnosing canine distemper can be challenging. Diagnosis usually requires a series of laboratory tests.

Serological diagnosis: This involves using CDV Vero cell cultures as known antigens to detect the serum of the tested dogs. Common methods include neutralization tests, complement fixation reactions, enzymelinked antibody assays, and immunofluorescence antibody assays.

Currently, CDV test kits are commonly used.

Section 5: Canine Distemper Prevention and Control Measures

Since dogs infected with CDV have weakened immune systems, they are highly susceptible to secondary bacterial infections. Therefore, when treating, it is essential to target both the virus and bacteria.

During the early stages of the disease, it is crucial to administer anticanine distemper serum in high doses as soon as possible, while also focusing on symptomatic treatment to prevent secondary infections and treatments to enhance the immune function. Passive immunization agents, such as hyperimmune serum, specific transfer factors, and canine leukocyte interferon, can be used, although they may not be effective in dogs that have already developed clinical signs of the disease.

For dogs with secondary infections, antibiotics and sulfonamide drugs can be administered, and drug sensitivity tests can be performed if necessary. Shuanghuanglian Injection, a traditional Chinese medicine, has shown some effectiveness in treating pneumonia caused by canine distemper virus. Human Shuanghuanglian Injection is also effective in treating pneumonia caused by secondary bacterial infections.

According to clinical symptoms, symptomatic and supportive therapies should be employed. This includes maintaining electrolyte balance, strengthening the heart and providing intravenous fluids, administering protein hydrolysates or amino acid injections, and using antipyretic and analgesic drugs. However, these measures can only alleviate symptoms and do not completely control the progression or outcome of the disease.

As of now, there is no highly effective treatment for canine distemper, and careful care can help promote recovery. It is important to increase the palatability of the diet, reduce activity levels, and ensure the dog rests in a quiet and comfortable environment. Regularly wipe the dog's eyes and nasal secretions with warm water. In winter, protect against the cold, and in summer, protect against the heat. During the spring and autumn, prevent secondary and concurrent diseases, and adjust the nutritional content of the diet according to the season to enhance the dog's immune resistance. Dogs should be kept in isolation, with free movement within the isolation area, and attention should be paid to disinfection and ventilation. Training and all vigorous activities should be stopped.

For susceptible dogs that have not been infected, emergency protective measures should be taken, including isolation and emergency vaccination. A reasonable immunization schedule and regular vaccination are the most important preventive measures. Some use human measles vaccine as the primary immunization, followed by canine distemper vaccine, which can also be effective.

Annually, CDV antibody and carrier checks should be conducted in canine populations. If dogs that are shedding or carrying the virus are identified, they should be culled immediately, and the site should be thoroughly disinfected.