4 Feb 2020
Jenny Stavisky discusses the prevalence and presentation of this issue, and why prevention is a risk for more than just shelter dogs.
Jenny Stavisky
Job Title
Infectious respiratory tract disease in dogs has traditionally been known as “kennel cough”.
It is increasingly recognised that this name is somewhat unhelpful, as it implies the disease only occurs in dogs in boarding kennels. Alternatives such as canine infectious respiratory disease complex, while accurate, are a bit of a mouthful.
In this article, the syndrome will be described as contagious cough (CC).
CC is a relatively common presentation in primary care practice.
In a recent study of more than one million canine clinical consultations, 0.9% were for respiratory disease, most commonly coughing.
Although it is impossible to determine how many were for CC, the most common presentation was for cough of shorter than a week’s duration, and more than a third of cases were prescribed systemic antimicrobials – suggesting a suspected infectious cause (Singleton et al, 2019).
A variety of pathogens are implicated in CC. Typically, an initial mild viral infection paves the way for a secondary infection with other opportunistic pathogens, so that disease is often multifactorial.
Common viruses implicated include canine parainfluenza virus (CPiV), canine respiratory coronavirus and type-two canine adenovirus. Secondary or opportunistic invaders may include Mycoplasma cynos and Pasteurella species, among others.
Bordetella bronchiseptica is capable of acting as a primary pathogen in its own right, as well as a secondary invader.
Over recent years, outbreaks of newly recognised pathogens have been seen.
Large-scale outbreaks of canine influenza virus have been seen in the US with resulting hotspots of infection – with high morbidity, but relatively low mortality.
The strain responsible, an avian-origin H3N2, was initially reported in south-east Asia. It may have spread to the US via exported rescues from the dog meat trade (Voorhees et al, 2017). Evidence exists that H3N2 can spread to cats (Jeoung et al, 2013), but it is not thought to have any potential for zoonotic spread.
No outbreaks have been reported in the UK yet, although seroevidence exists of infection with an earlier H3N8 strain of likely equine origin (Daly et al, 2008).
Streptococcus equi subspecies zooepidemicus has been seen intermittently, including a number of UK cases. Often seen in dogs in kennels and shelters, this can vary in presentation – from a mild cough with mucopurulent nasal discharge, to peracute death. In outbreaks, high mortality rates have been reported – even in treated dogs – likely due to the acute onset (Pesavento et al, 2008).
Co-infection with other CC agents is thought to perpetuate infection and increase severity (Priestnall and Erles, 2011).
Clinically, the classical presentation for CC is a hacking cough, which is sometimes productive.
Owners may present these dogs as retching, gagging, or “with something stuck in its throat”. The cough may be accompanied by pyrexia, ocular or nasal discharge, submandibular lymphadenopathy and a mild to moderate degree of malaise.
Pinching the trachea – initially mildly, then with escalating pressure (within reasonable limits) – will often result in a spasm of coughing, which is not pathognomonic of CC, but indicative of upper respiratory tract inflammation or sensitivity. Often, a gentle tracheal squeeze is sufficient to make a dog gag or gulp slightly, and it is unnecessary to apply more pressure.
Such cases will usually resolve with no treatment, or supportive treatment such as NSAID medication.
Some clinicians choose to use cough suppressants. However, in acute and productive cases, these may suppress the body’s own mechanism for ridding itself of pathogens, so should probably be reserved for non-resolving cases where a chronic inflammatory component exists to the cough.
Antibacterials are not usually indicated for CC. Both the BSAVA and International Society for Companion Animal Infectious Diseases recommend antibacterials are reserved for severe or non-resolving cases, and recommend the use of doxycycline or potentiated amoxicillin in the first instance (BSAVA and Small Animal Medicine Society, 2018; Lappin et al, 2017).
In the author’s experience – especially in a shelter situation – early antimicrobial treatment can also be helpful in limiting severe disease where dogs are particularly susceptible to secondary infection. This would include young puppies, very brachycephalic dogs and those with pre-existing cardiorespiratory disease.
Where severe or non-resolving disease is seen in an individual dog, thoracic radiography and bronchoalveolar lavage – with accompanying culture and sensitivity – are indicated.
Other differentials – including non-infectious causes of bronchitis, Angiostrongylus vasorum and neoplasia – should be considered.
Where severe disease is seen in a population, such as in a kennel or shelter, it is essential to perform a full evaluation of the site.
Factors such as intake policy, vaccine protocol, source of dogs, and presence and use of quarantine and isolation should be assessed.
The cleaning regime should be observed, if at all possible, to ensure detergent cleaning precedes disinfection, that a suitable disinfectant at an appropriate dilution is used, and that no caustic chemicals are in use.
Most importantly, the ventilation in the housing should be assessed. Although it is usually not feasible to formally measure the number of air changes within dog housing, simply standing in the housing for a few minutes to see if the air feels damp or stuffy can give a general impression of how adequate, or otherwise, the airflow is.
Diagnostics are indicated within a population where an unacceptable incidence occurs, the incidence of disease increases, disease patterns change, or when considering implementation of a new management strategy (for example, introducing new vaccines).
Deep oropharyngeal swabs are usually easier to perform, better tolerated and more successful in recovering pathogens than nasal swabs.
Where canine distemper virus is suspected, conjunctival swabs may also be helpful – check with your relevant diagnostic lab.
Sample several dogs, preferably at different stages of infection, bearing in mind the potential roles of different pathogens.
Occasional reports exist of zoonotic transmission of S equi subspecies zooepidemicus.
While relatively uncommon, these have resulted in severe disease in the people affected – including meningitis, septicaemia and endocarditis (Zahlanie et al, 2019; Abbott et al, 2010; Høyer-Nielsen et al, 2018).
Likewise, concerns about the zoonotic potential of Bordetella are frequently raised. Although rare, zoonotic cases of Bordetella with a suspected canine or feline origin have had serious sequelae (Brady et al, 2014).
Zoonotic transmission following administration of a live vaccine is rarer still, but should not be disregarded (Gisel et al, 2010). Most cases of zoonotic transmission have occurred in either cystic fibrosis or transplant patients.
Reasonable steps to protect people in contact with infected, or recently vaccinated, dogs should be made – whether by discussion with clients, waiting room signs or other means.
Vaccination is the cornerstone of CC prevention where Bordetella is implicated; some vaccines include CPiV alongside Bordetella.
It is estimated about 60% of dogs in the UK are vaccinated annually; however, only about a third of these receive an intranasal Bordetella vaccination (UK Pharma National data, Kynetec).
Interestingly, a social media survey of 171 UK vets revealed 47% always or usually recommended CC vaccination; 46% sometimes recommended it and 6% rarely or never recommended it. Those who recommended it did so largely because they perceived their patients were at significant risk of contracting it (42%), and that CC could cause severe disease (34%). Those who recommended it less frequently did so largely because they perceived CC as a mild disease (29%) and because dogs found CC vaccination an aversive experience (36%; unpublished data).
These differences in vets’ perceptions of the importance, severity and frequency of CC may be due to differences in caseloads and populations at different locations.
It is interesting the potentially aversive experience of administering the vaccine may be a decision in whether to use it. From a personal perspective, the reason the author included the question in the survey was from realising that has actually been quite a strong factor in her attitude towards CC vaccination.
This may be due to being old enough to recall using the earlier generation of CC vaccines, which required administration of a full millilitre of vaccine every six months. The vaccine itself smelled disgusting, even to a human nose, and was no doubt even more revolting to a sensitive canine olfactory system.
Modern vaccines are, of course, much less aversive to administer.
A range of measures may make intranasal vaccination less aversive still. These include keeping the diluent at room temperature, covering the dog’s eyes, provision of high-value food treats and gentle administration (trickle, don’t squirt).
The recent launch of an intraoral vaccine for Bordetella will also offer an alternative that may be better tolerated by some patients.
Licensed intranasal vaccines have an onset of immunity (OOI) of three to five days. The new oral vaccine is licensed for an OOI of 21 days – meaning where urgent protection is needed (for example, intake of stray dogs to a shelter), intranasal vaccines would be the better choice.
However, one study comparing oral with intranasal vaccines showed a good efficacy of both when challenged at seven days post-vaccination (Scott-Garrard et al, 2018) – so it is possible an earlier onset of immunity will be seen in the future.
Where exposure to respiratory disease can be predicted in advance, having two possible routes of administration should enable a wider vaccine coverage within the population.
In summary, we may do our patients a disservice if we regard CC as purely a risk for dogs going into kennels.
Many of our dogs socialise with groups of others – whether at the play park, agility sessions, doggy daycare or in our own clinics.
CC is usually self-limiting, but can cause severe disease in some individuals. For those of us suffering from the current season’s round of upper respiratory tract disease, we may be reminded even relatively mild disease can be very uncomfortable, and worth preventing where possible and appropriate.
