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Cat Flu


Cat flu can be an acute or chronic condition. Young, elderly and immune-suppressed animals are particularly at risk.

Cat flu or cat flu complex, also known as feline upper respiratory tract disease (FURTD), is a multifactorial disease. This means that clinical symptoms are generally the result of a combination of various factors.

However, pathogens that can cause the symptoms on their own (primary pathogens) include feline herpesvirus and feline calicivirus. The disease often takes an acute form but can also become chronic. In chronic cases, animals either suffer continually from eye discharge and sneezing or develop recurring flare-ups.

Large populations of animals, for example in animal shelters, catteries and multicat households, are particularly at risk. However, immune-suppressed cats such as found animals and young or elderly cats are also at higher risk. Other contributory factors are poor hygiene conditions, frequent contact with other animals and, invariably, stress.

In the event of infection, the use of a hyperimmune serum can boost the recovery process.

Cat with slightly watery eyes


A distinction is made between viral primary pathogens and bacterial (secondary) pathogens.

The primary pathogens responsible for cat flu complex are feline calicivirus (FCV) and feline rhinotracheitis virus or herpesvirus (feline herpesvirus type 1, FHV1). Besides viruses, Chlamydia, Mycoplasma and Bordetella bacteria also play a role as possible primary pathogens. Bacterial infections with Pasteurella, Escherichia coli, Pseudomonas, Streptococci and Staphylococci are usually secondary. After surviving an infection, cats often remain carriers of FCV and FHV for many weeks or even years.

Yawning Cat


Depending on the virus, animals develop a local or systemic infection. The main symptoms are eye and nasal discharge.

Both viruses enter the body via the mucous membranes of the nose and throat, where they replicate.
Whereas herpesvirus causes a local infection, caliciviruses produce a systemic infection. Both virus types can induce a persistent infection, in which the virus can be excreted intermittently (herpesvirus) or continuously (calicivirus) over a period of weeks or months.

The first disease symptoms usually appear 2-6 days after infection. Infections are often observed in situations of crowding. In these cases, outbreaks are associated with stressful situations or other triggering factors. This is why the cat flu complex is described as a multifactorial disease.


The clinical symptoms of calicivirus infection include:

  • Mild sneezing, conjunctivitis
  • Lesions on the margins of the tongue
  • Pneumonia
  • Chronic inflammation of the gums and mucous membranes of the mouth

Reports from the USA, UK and Germany describe the emergence of new and particularly harmful strains of calicivirus, or "virulent systemic (vs)" FCV, which produce serious clinical pictures and cause epidemics accompanied by high mortality rates of up to 50 %.

Characteristic signs are:

  • High fever
  • Tongue and foot pad lesions
  • Oedema (fluid retention)
  • Haemorrhage (bleeding)

Remarkably, some of the outbreaks described in the USA even concerned vaccinated cat colonies.

Cat with mucosal damage in the mouth
Mucosal damage ( Source: Wikipedia)


The clinical symptoms of herpesvirus infection include:

  • Sneezing
  • Watery discharge from eyes and nose, later often with pus
  • Bouts of fever
  • Lack of appetite
  • Conjunctivitis and corneal ulcers, sometimes lasting several weeks
  • Mucous membrane defects on the tip and back of the tongue
  • Inflammation of the upper respiratory tract
  • Possibly coughing
  • Pneumonia

Long-term consequences include chronic sinusitis and chronic secondary infections.

In female cats, infection can also lead to miscarriage and kitten deaths.

Cat with mucosal damage in the eye
Mucosal damage ( Source: Wikipedia)


The clinical picture is usually obvious. Special laboratory tests or viral culture need to be carried out in order to identify the virus.

In an acute case, the diagnosis can generally be made on the basis of the animal's history and clinical symptoms. Oral or nasal swabs are suitable for detecting both viruses. Swabs are then analysed in the laboratory, either bypolymerase chain reaction (PCR) or by viral culture.

Multichannel pipette


Treatment consists of the administration of a hyperimmune serum and therapeutic measures tailored to the symptoms.

Symptomatic treatment: if the animal's food and water intake are reduced, fluid and electrolytes should be replaced. An animal suffering from bacterial secondary infections should also be given an antibiotic.

In addition, the eyes and nose should be kept free of mucus and discharge.

Symptomatic treatment alone is usually not sufficient. In an acute case, the affected animal should be treated as quickly as possible with a hyperimmune serum. This contains neutralising antibodies to FCV and FHV, providing immediate support for the immune system in fighting the disease.

The hyperimmune serum is obtained from donor animals that have been immunised multiple times. Multiple immunisation causes the donor animals to produce higher levels of antibodies. After careful collection and further processing, they become purified, highly effective antibodies available for use in prevention and treatment.

In contrast to non-specific stimulation of the immune system using paramunity inducers, the effect is immediate. The use of a hyperimmune serum therefore buys valuable time in the fight against infectious disease!

Veterinarian with kitten

Preventive Measures

Vaccines are available for use from the 8th week of life. In addition, hyperimmune sera offer protection during the immunological gap.

Various vaccines protecting against FHV and FCV are available for use from week 8. The basic vaccination programme includes a second vaccination at the age of 12 weeks, a third at 16 weeks, and a fourth at 15 months. After that, free-roaming cats or animals with particularly high exposure should receive an annual booster, while cats at low risk only need to be reimmunised once every two years.

In populations with cat flu problems that remain uncontrolled despite vaccination, it may be appropriate to use vaccines with different FCV vaccine strains. This is because FCV isolates display marked antigenic variability, which does not induce cross-neutralisation between isolates.

Kitten gets medicine from the veterinarian

In addition, during the immunological gap, or generally in animals assumed to have increased susceptibility to infection, the preventive use of an antibody serum to provide temporary protection for offspring or weakened animals may be advisable.

The immunological gap is the period in which the maternal antibodies no longer provide sufficient protection for offspring, but are still present in concentrations high enough to block the vaccine antigen and hence the development of active vaccine-induced immunity.

The antibodies in the hyperimmune serum from IDT Biologika Animal Health provide valuable support in the treatment and prevention of cat flu. They have immediate therapeutic effect and protect against reinfection.

As further measures, the conditions in which the animals are kept should be improved if need be, and stressors identified and eliminated wherever possible.

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