Overview

Does your pet or farm animal have a cough or a sneeze? Parainfluenza is one such viral disease that can cause respiratory signs in humans and many other mammals. This is the same disease known as croup in humans, kennel cough in dogs and shipping fever in cattle³. Canine parainfluenza virus (CPIV) and bovine parainfluenza virus (BPIV) are the two most common parainfluenza virus types affecting animals.

Parainfluenza alone produces only mild clinical signs that resolve even without treatment. However, the significance of the disease is that it is highly contagious, and the virus promotes secondary viral, bacterial and mycoplasma infections. Co-infections can make an animal critically ill, resulting in pneumonia and prolonged recovery. Furthermore, parainfluenza viruses affecting some animals are zoonotic. Nonetheless, parainfluenza can be prevented with proper management practices and vaccinations. 

Types of parainfluenza viruses in animals

Canine parainfluenza virus (CPIV) 

The parainfluenza virus type which affects dogs is called canine parainfluenza virus. This is a major organism causing the widespread respiratory disease in dogs, known as kennel cough or canine infectious respiratory disease complex (CIRDC).⁶ Severe respiratory disease is more common when co-infected with mycoplasma infections.¹³

Although CPIV has been identified in humans, the zoonotic potential is unknown.¹³

Clinical signs and symptoms

During parainfluenza infections, dogs may show a dry cough lasting 2-6 days, sneezing, salivation, swallowing difficulties, poor appetite and lethargy. Fever is uncommon.⁶ Severe cases can lead to pneumonia by increasing susceptibility to secondary bacterial lung infections.¹³ A dog may show symptoms 2-8 days after exposure to a diseased animal.⁶

Modes of transmission 

The disease is highly spreadable, especially in overcrowded kennels and among immunocompromised animals. A diseased individual starts spreading the infection 2-10 days post-exposure; thus, spreading occurs before showing clinical signs. Infection transmission is through aerosols and fomites⁶. 

Diagnosis and detection

Parainfluenza, when uncomplicated, resolves spontaneously. Therefore, definitive diagnosis is necessary only when clinical signs persist for more than 7-10 days, if the condition is complicated by pneumonia or when there is a high infected population.¹³

Identifying the causative agent is impossible only upon symptoms, as many respiratory infectious diseases manifest similar signs. Blood tests will not specifically indicate viral respiratory infections but can depict the disease severity and provide evidence of secondary infections. Radiographs will be used to diagnose secondary pneumonia.¹³

A definitive diagnosis of parainfluenza can be made by Polymerase Chain Reaction (PCR) testing of nasal swabs and transtracheal aspirates.¹³ A transtracheal aspirate is a respiratory secretion obtained from the lower airways and lungs.⁹ PCR is a method for identifying the virus through its unique genetic material and is sensitive and very specific for virus identification.⁸

Treatment and management

Medical treatment

As for the common cold in humans, contagious respiratory diseases in dogs resolve without treatment despite the root cause of the disease. Unless the pet is lethargic and has a low appetite,  treatment is unnecessary for symptoms less than 7-10 days. 

Symptomatic treatments, such as bronchodilators and cough suppressants, may be given if signs persist for more than ten days.^12,13

Treatment of secondary infections

As secondary infections are possible, broad-spectrum antibiotics will be used. As the development of resistance to antimicrobial drugs is increasingly common, antibiotic therapy should be initiated after culture and sensitivity testing of samples.^12,13 However, antibiotics are indicated when there is clear evidence of secondary bacterial pneumonia and pus-like discharge from the eyes and nose.¹³ Furthermore when mycoplasma infections are suspected, anti-mycoplasma drugs will be given as the first choice.^12,13

Supportive care 

If the patient is prolonged or critically ill, supportive treatment will be given¹². Intravenous fluids will be administered to maintain adequate fluid and caloric intake. Pneumonic patients may require oxygen supplementation and nebulisation. If the dog has complete inappetence, your vet may provide nutritional support by feeding tube insertions.^12,13

Prevention and control

In 1970, Attenuated CPIV vaccines were introduced. These included B. bronchiseptica, the other main bacterial agen causing kennel cough^[11]. For CPIV, modified live vaccines and other viral and bacterial agents are available. Although CPIV is not considered a ‘core’ vaccine, meaning an essential vaccine, as the other agents in the combination are essential, vaccinating against CPIV is a standard practice in most countries.⁶ 

CPIV vaccines available in the intranasal route constitute other CIRDC agents as well. Thus, these vaccines have a greater effect on kennel cough.⁶ As these are modified live vaccines, these intranasal vaccines produce better immunity against kennel cough causative agents than inactivated vaccines given via the parenteral route. Despite vaccines producing immunity against CPIV for over a year, annual vaccinations are recommended as only a limited immunity develops against the bacterial agents in combined vaccines.¹⁰

Bovine parainfluenza virus (BPIV)

BPIV was first identified in the United States in 1959 and since then, has been found commonly worldwide, causing respiratory tract infections in ungulates.^4,5 On its own, the virus may cause asymptomatic infection or a mild respiratory disease, but mostly, it increases the vulnerability to secondary viral, bacterial and mycoplasma infections. Therefore, BPIV is a major cause of the bovine respiratory disease complex. Mixed infections mostly occur due to long-distance transportation stress reducing the animals’ immunity and increasing susceptibility to infection. Hence, named the ‘shipping fever.⁵

BPIV is zoonotic.^5,11 However, the BPIV spreading from one person to another is rare.⁵

Clinical signs and symptoms

The infection results in fever, lack of appetite, cough, sneezing, nasal and eye discharges,  and increased breathing rate and sound. In calves, lambs and kids, the virus largely remains subclinical. In other animals, the virus may show mild symptoms with a low illness rate. 

BPIV rarely produces severe respiratory disease and pneumonia as the sole infectious agent. Thus, death due to uncomplicated BPIV is rare. Generally, clinical signs worsen with secondary infections resulting in inflammation in the airways and lungs. Thus, fatality mostly owes to concurrent bacterial pneumonia.^5,7

Transmission and host range

Although BPIV is a primary ruminant virus, it has a wide host range. It predominantly infects cattle, sheep and goats but has also been identified in water buffaloes, camels, horses, pigs, dogs, monkeys and humans^4,5,7. The disease has been reported in a healthy fallow deer and one mule deer in the wild. The virus spreads by aerosols or formites contaminated with discharges⁷. 

Treatment and management

Treatment for BPIV is limited to supportive treatment to keep animals hydrated and maintain proper caloric intake and electrolyte balance. Antibiotics are given if they do not recover with supportive measures and diagnosed with secondary bacterial infections. Anti-inflammatory drugs such as non-steroidal anti-inflammatory drugs (NSAIDs) are administered to reduce fever and lung inflammation. This will lead to animal welfare improvement and increased feed and water intake. However, corticosteroids, anti-inflammatory drugs, are not recommended as they can reduce immunity.¹⁴

Diagnosis and detection

Respiratory infections are diagnoses based on clinical examination and diagnostic imaging. However, identifying the specific causative agent is not possible by these methods, and for virus identification, more specific methods are needed.¹⁴

Commonly used samples for diagnosing PIV are nasal swabs and transtracheal aspirates.¹⁰ There are three diagnostic techniques for confirmatory diagnosis of BPIV.¹⁴

• Virus isolation in cell culture
• PCR
• Immunoassays 

Virus isolation in cell cultures is a specialised technique for diagnosing PIV infection. The advantage of this technique is that it can identify other nonconcurrent viral infections during PIV infection.⁸ This was used as the gold standard.^8,14

Lately, PCR has been commonly used to detect PIV.² PCR is more sensitive to virus detention compared to cell cultures.¹⁴

Immunoassays are currently widely used due to their high sensitivity and ability to provide quick results. Immunoassays are methods to identify the specific antibodies against a viral antigen. Viral antigens are proteins in a virus which trigger an immune response in an animal.² ELISA is an immunoassay, considered the best diagnostic tool for PIV identification.³

Prevention and control

Vaccination is the most effective method for managing BPIV in herds, but appropriate biosecurity measures are important for prevention and control.¹⁴

Vaccines for BPIV were first developed in 1960. Since then, live attenuated and inactivated vaccines have been given parenterally or intranasally. However, currently used vaccines against BPIV are combined with other viral and bacterial antigens that produce BRDC to produce complete immunity against shipping fever.⁵

BPIV outbreaks can be controlled and prevented by sanitation practices, as normal disinfectants also can inactivate the virus.¹⁴

Other parainfluenza viruses

Terrestrial wild animals have been largely found exposed to parainfluenza. Bison in Alaska, rhinoceros in South Africa and white-tailed deer in Quebec are a few examples. Moreover, the parainfluenza virus was found in bottlenosed dolphins, indicating the disease in aquatic animals.¹⁵

Pangolins, virus reservoirs, have been found harbouring parainfluenza viruses, including the human parainfluenza virus³. Therefore, pangolins act as a zoonotic threat for parainfluenza.¹⁶

Furthermore, the parainfluenza virus has also been isolated in pigs, rats, rabbits, foxes, and cats and recently was identified in a Siberian tiger.⁵ These suggest the necessity of further research for inter-species transmission and evolution of the parainfluenza virus.¹⁷

Conclusion

Parainfluenza is a contagious viral infection affecting a wide range of mammals. Common clinical signs in affected individuals are cough, sneezing and low appetite. The disease is a mild infection but can lead to secondary infections and pneumonia. The common parainfluenza viruses are bovine parainfluenza virus, which affects cattle, sheep, and goats, and canine parainfluenza virus, which infects dogs. However, other parainfluenza viruses have been isolated in wild animals. Although respiratory disease can be diagnosed through clinical signs, identifying the exact virus is necessary when a shelter or a herd is affected. More specific viral tests are needed for these. However, parainfluenza infections are self-limiting if complicated, symptomatic, supportive and antimicrobial therapy will be necessary. Proper management procedures and vaccinations can achieve control of parainfluenza infections. Therefore, if your animal is affected by a respiratory condition, consult your veterinarian before complications arise.