Unfortunately, infectious disease treatment is something nurses deal with regularly in veterinary practice. As veterinary professionals, we have some responsibility to educate pet owners on the prevention and control of infectious diseases in their pets. For this reason, it is important to understand the disease you are trying to prevent or control. So, let’s look at some key points and factors for the more commonly recognised infectious diseases in small animal practice.
Canine infectious diseases commonly seen in practice
Canine herpesvirus
Herpesvirus may not be one of the infectious diseases that springs to mind immediately; however, it is something we really need to educate owners about, especially the owners of breeding bitches.
While mild respiratory symptoms are signs of the disease in adult dogs, herpesvirus is a common cause of abortion and stillbirth in pregnant bitches. If the disease is transferred to newborn neonates, it causes the syndrome known as “fading puppy syndrome”, which is often fatal. If the neonates do survive, they can be left with long-term neurological deficits. The virus has a preference for temperatures lower than a dog’s normal body temperature, which is why it is so important to keep neonates warm – if they get cold and have been exposed to the disease, this is when it can take hold.
While mild respiratory symptoms are signs of the disease in adult dogs, herpesvirus is a common cause of abortion and stillbirth in pregnant bitches
There is a vaccination available for canine herpesvirus, which has to be given in two doses at each pregnancy. In a breeding environment, it is suggested to isolate pregnant bitches from other dogs in the three weeks before whelping is due. The vaccine is inactivated by ultraviolet light, lipid solvent detergents and exposure to heat of 56°C for 30 minutes. Owners may ask about testing their bitches for the disease prior to mating, but the disease can be latent, and if the polymerase chain reaction (PCR) test is run during this time, you will receive a negative result.
Canine infectious respiratory disease complex
Traditionally known as “kennel cough” to many pet owners, this infectious disease begins with a hacking-type cough, which, at the end of a coughing session, may also include the production of some white foam/saliva. Owners who have not witnessed kennel cough before may phone their vet panicking, believing their dog is choking on something as it is such a deep hacking cough. Occasionally nasal and ocular discharge may develop along with anorexia, although this is more common in young, elderly or compromised patients where a secondary infection develops.
The disease is a combination of infectious agents, which can include:
- Bordetella bronchiseptica
- Parainfluenza virus
- Canine adenovirus
- Mycoplasma canis
- Respiratory coronavirus
- Influenza virus
- Canine distemper virus
- Canine herpesvirus
Bacterial involvement is signposted by mucopurulent nasal discharge, pyrexia, lethargy or anorexia. Kennel cough is contracted via inhaled infective aerosols or fomites, normally in close contact or shared air spaces, which is from where the “kennel” cough name is derived. However, the disease can be contracted on a dog walk, while visiting friends, at a dog show or anywhere where two dogs are in close proximity and the same air space. The incubation period of the disease is from 2 to 18 days, depending on which viruses combine to form the condition, and clinical signs commonly last for two to three weeks.
Treatment for this condition is often symptomatic. Owners will often request antibiotics; however, antibiotics are not required unless bacterial involvement is suspected. Restricting exercise to minimise coughing episodes due to increased tidal flow, avoiding using a lead on a collar as it puts pressure on the trachea, feeding soft food and avoiding moving from an area of warmth to cold will all help to alleviate the symptoms. Sometimes, the use of antitussives can be beneficial, not only for their respiratory properties but also to help the pet rest as they have mild sedative properties. So, the use of these in the evening before bedtime can be beneficial to help the dog to rest and sleep overnight.
Vaccination is possible for kennel cough; however, one vaccine type does not cover all potential variants of the disease
Vaccination is possible for kennel cough; however, one vaccine type does not cover all potential variants of the disease. Therefore, the patient may still contract the disease, but the symptoms will be milder. If using the intranasal vaccine, it is important to be aware of the risk if the owner is immunocompromised.
Canine parvovirus
Canine parvovirus is one of those horrible diseases – once you have smelt the diarrhoea produced by a parvovirus sufferer, you never forget the smell! The disease causes acute vomiting, diarrhoea and fever, quickly followed by dehydration and lymphopenia. Mortality is high, especially in puppies, because the virus is so debilitating. The disease can survive in the environment for years if disinfection is not thorough enough or suitable for the virus. Furthermore, it is thought that environmental contraction of parvovirus is more of a concern than contact with an infected dog. The disease cells replicate in the gastrointestinal tract and following five to six days of infection, the intestinal mucosa becomes involved. This is when you see the diarrhoea beginning to look like the animal is literally defecating its gut lining.
It is thought that environmental contraction of parvovirus is more of a concern than contact with an infected dog
Treatment or control of the parvovirus in a patient is intense but crucial to increase any chance of survival. Treatment steps can involve:
- Interferon medication: this has shown positive results; however, it is costly and may be out of the scope of some owners
- Replacing fluid and electrolyte losses
- Antibiotics: these are often used to prevent secondary sepsis from developing
- Anti-emetics to control vomiting
- Nutrients via feeding: this may require a feeding tube as patients often feel too unwell to eat
- Hygiene: this is crucial – remove any faeces/vomit as soon as it occurs and follow this with effective cleaning and disinfection. Bleach is often deemed the more appropriate disinfectant
Confirmation of the disease is traditionally done via blood or faeces for serology or virus isolation; however, there are now commercial “snap” tests available for same-day answers.
Canine adenovirus
Traditionally referred to as infectious canine hepatitis, canine adenovirus is fairly hardy and can survive in the environment for months. It is also resistant to many disinfectants except quaternary ammonium compounds. A temperature of 56°C or above kills the disease; therefore, it is recommended in practice to steam clean any kennels the patient has resided in, as well as disinfecting them. The adenovirus infection enters via the oronasal route and begins replication in the tonsils and then the regional lymph nodes. It has an incubation period of four to seven days. Patients present with various clinical signs, including:
- Abdominal pain (often due to hepatomegaly)
- Paleness
- Pyrexia
- Corneal oedema (“blue eye”)
- Lymphadenopathy
- Incoordination
- Petechiae
It is important to note two things about this disease:
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Treatment of this disease includes supportive treatments based on clinical signs, such as fluid therapy, nutritional support, anti-nausea medications and, in many cases, blood transfusions. A broad spectrum antibiotic is also advocated prophylactically. Patients with mild cases tend to recover in one to two days, whereas patients with a moderate disease process require three to five days of care. Severe forms of the disease can result in death.
Feline infectious diseases commonly seen in practice
Feline viral-induced upper respiratory tract disease
Commonly referred to as “cat flu”, this disease is caused by two common viruses: feline herpesvirus and feline calicivirus. It is a condition which can be seen in any age of cat, but you are more likely to see young cats with the acute form of the disease and older adult cats with more chronic symptoms. Presenting signs can include any, and often several, of the following signs:
- Oculonasal discharge
- Depression
- Pyrexia
- Anorexia
- Sneezing
- Salivation
- Coughing
- Odynophagia
- Oral/ocular ulceration
The incubation period for the disease is 1 to 14 days, and most acute clinical signs resolve within one to three weeks. However, regardless of whether the infection was herpes- or calicivirus-derived, the cats will become carriers. Cats carrying calicivirus will excrete the virus continuously for variable lengths of time, some for months to years, with others shedding for the rest of their lives. Cats that have had herpesvirus are latently infected for life, with shedding and potential manifestation of clinical signs recurring following periods of stress, pregnancy or corticosteroid administration.
Hygiene is important to prevent the spread of cat flu, as the virus is fairly hardy in the environment
Diagnosis is usually achieved via virus isolation from either oropharyngeal or conjunctival swabs. Treatment is varied and includes:
- Supportive nursing care, such as cleaning secretions and grooming
- Fluid therapy and nutritional support: it is not uncommon for these patients to require tube feeding
- Broad-spectrum antibiotics with good penetration in the respiratory tract
- Antivirals
- L-lysine: this has been suggested as being beneficial, but the real clinical benefit is unknown
- Pain relief: if oral or ocular ulceration is bad, then pain control should be established
Hygiene is important to prevent the spread of cat flu, as the virus is fairly hardy in the environment; fomites can be a source of transmission as well as direct cat-to-cat transmission or oral and nasal secretions.
Feline immunodeficiency virus
This disease is commonly known as FIV. When HIV was first mentioned in humans, a similarity was suggested between that and FIV, but it is important to ensure owners realise this disease is not zoonotic.
The disease is primarily transmitted through saliva, so the most common cause of contracting the disease is following a bite from another cat. This is why FIV is more common in male cats than female ones, as they tend to fight more. The good thing about the FIV virus is that it cannot survive outside the body, so fomites contaminated with saliva tend not to be a concern. However, once the cat is infected, they have it for life, and they are often asymptomatic for years following infection. Once the disease progresses clinical signs which may develop include:
- Gingivitis
- Pyrexia
- Recurrent infections
- B-cell lymphoma
There is no treatment for the actual disease, but interventions can help with clinical signs. Interventions tend to be symptomatic and supportive. Diagnosis is commonly obtained using immunomigration tests, eg snap tests, in practice; however, as there is a chance of a false negative or false positive, a PCR test is often used as a formal diagnosis afterwards.
Feline leukaemia virus
Commonly known by the abbreviation FeLV, the feline leukaemia virus has three presenting formats: immunosuppression, proliferative (neoplasia and leukaemia) and degenerative (anaemia and leukopenia).
FeLV does not survive well outside the body or bodily fluids, therefore survival on fomites, such as food bowls, is negligible. However, it is important to be aware that large amounts of the FeLV virus are shed in saliva and can also be shed in urine and milk. The general incubation period between infection and viraemia is two to three weeks. It is also important to remember that FeLV-positive cats can remain healthy for months to years before external clinical signs develop. If you know a cat is FeLV positive during this time, it should be isolated from other cats, as it is still possible for healthy FeLV-positive cats to transmit the disease.
While there is no treatment as such, there are some control measures to improve the patient’s quality of life, including:
- Interferon-omega
- Antiretroviral
- Avoiding immunosuppressive medications
- Blood transfusions (these may be required in anaemic cats)
- Chemotherapy for lymphoma
Vaccination is recommended for any cats going outside and mixing with other cats, with vaccination starting from nine weeks of age.
It is important to consider testing any feline patients seen repeatedly for pyrexia, non-healing abscesses and recurrent upper respiratory tract infections for FeLV
Diagnosis of the condition is often achieved using immunomigration tests, eg snap tests, in practice, but these can give false negatives and positives, so if suspicion of FeLV is high, then diagnosis via PCR or virus isolation is recommended. It is important to consider testing any feline patients seen repeatedly for pyrexia, non-healing abscesses and recurrent upper respiratory tract infections for FeLV.
