Taken from a talk given by Professor Danielle Gunn-Moore from the University of Edinburgh at a Petplan FAB Breeders symposium. 

Kitten deaths are a cause of concern and distress to anyone involved with breeding cats.. In part 1 of this article we looked at some of the causes of death of kittens at or soon after birth. In general, infectious diseases are involved in relatively few early kitten deaths, however, they can result in significant deaths in kittens from three to four weeks of age onwards.

Protection for kittens
Kittens gain protection from infectious disease from their mother in the form of antibodies which are present in the colostrum, the milk which is produced soon after birth – these antibodies (called maternally derived antibodies [MDA]) are absorbed efficiently from the kitten’s digestive system for up to six hours after birth, but by around 48 hours they are not absorbed at all. These antibodies protect the kitten’s intestines by preventing disease organisms from passing through the gut into the kitten’s blood. They are also absorbed into the kitten’s blood stream where they can fight any infections that get into the kitten by any other route (e.g. through the umbilicus, skin or lungs.

A queen will have antibodies to infectious organisms that are currently present in her environment and these will be passed on to the kittens. Therefore it is important that she lives in the same environment before and after giving birth so that the kittens get protection against the infectious agents that are found there.

The protective effect of these maternal antibodies usually begin to fade when the kittens are three to four weeks of age. The kittens’ natural immunity is still developing at this time, and since most vaccine regimens do not start until around eight weeks of age, this can leave a period of time when the kittens are particularly at risk from these infectious diseases. Kittens that do not suckle will receive insufficient colostrum and so will not be protected by MDA: because of this they may develop infectious disease at any point after birth, often dying within the first week.

A healthy kitten should be able to cope with a low level of infectious organisms within its environment. It will generally experience no more than occasional mild and brief signs of illness. However, if the kitten’s immune system becomes suppressed, serious disease or fatal infections may occur. Factors which may contribute to an inadequate immune response include inadequate colostrum intake, inadequate nutrition, low birth weight, lack of oxygen at birth, congenital disorders (especially of the immune system), previous trauma or infection, a low environmental temperature, or an unhygienic environment leading to a build-up of contamination with infectious agents. Respiratory and gastrointestinal infections are seen most frequently.

Viruses
Cat flu viruses
The cat flu viruses (feline calicivirus [FCV] and feline herpes virus [FHV-1]) are perhaps the most commonly seen viral infections of kittens. While in healthy kittens infection may be mild and brief, weak kittens may develop more severe clinical signs or secondary bacterial infections. FHV-1 infection may also be associated with abortion.

Feline coronavirus
Feline coronavirus infection (FCoV), like the cat flu viruses, is hard to eliminate from places where there are a number of cats – rescue or breeding catteries for example. When present, infection may be associated with an increased incidence of reproduction failure, abortions and stillbirths. Affected kittens may show signs of diarrhoea, malaise, or ‘fading’, and occasional cases of more classical effusive feline infectious peritonitis (FIP).

Feline panelukopenia virus
Feline panleukopenia virus (FPV) is usually seen in catteries that fail to vaccinate properly. However, it is occasionally seen in kittens from vaccinated queens, possibly resulting from severe environmental contamination. Infection may result in abortions, stillbirths, fading kittens, diarrhoea, panleukopenia (bone marrow suppression resulting in a lack of red and white blood cells), septicaemia (see below), cerebellar ataxia (uncoordinated walking), and/or death.

Feline leukaemia virus
Feline leukaemia virus (FeLV) has been almost eliminated from the pedigree breeding population in many countries. Neonatal disease caused by this infection is therefore seen mainly in rescue catteries. In this situation it may result in reproductive failure, abortions, stillbirths, fading kittens, a panleukopenia-like syndrome, septicaemia or death.

Where infectious disease is suspected it is important to ensure that the queens’ vaccination programme is up to date. Since kittens gain some protection from infectious disease in the form of MDA passed in the colostrum, in breeding catteries it may help to give booster vaccines before mating.

Bacteria
In kittens, bacterial infections are often seen secondary to viral infection (cat flu, FeLV, FIV, FPV, FIP). However, bacterial infections can also be seen without prior viral infection. In most cases the bacteria originate from the queen’s birth canal (beta haemolytic Streptococcus sp. [Strep G infection]), gastrointestinal tract (E coli, salmonella, campylobacter and many normal intestinal bacteria), or respiratory tract (Bordetella, Pasturella or Mycoplasma). Clinical signs depend on the site, nature, and severity of the infection. They may include diarrhoea, coughing, breathing difficulties, arthritis, or dermatitis, as well as the less specific signs more typical of fading kittens.

Ultimately, many of these infections may result in septicaemia (a severe type of infection in which the blood stream is invaded by large numbers of bacteria which multiply and spread) and death. The increased risk of this type of infection in neonates results from the factors listed above, especially failure to ingest enough MDA from the colostrum. In addition, new born kittens are predisposed to problems associated with hypoglycaemia (low blood sugar - see part 1 of this article) and intestinal distension (especially when cold) significantly increases the risk of bacteria entering into the blood stream. The infection itself can then make the kittens more prone to hypothermia and hypoglycaemia.  Disease may be very sudden or may run a slower course. While the signs of illness may be varied, they frequently result in slowing of the heart rate, difficulty in breathing, dehydration, weakness, crying, seizures, coma and death. Septicaemia often occurs as the final stage of other conditions, and is particularly associated with systemic viral infections. The most common cause of this are gram-negative bacteria, but can include; streptococcus, E coli, staphylococcus, klebsiella, enterobacter, enterococcus, pseudomonas, clostridium, bacteroides, fusobacterium, pasteurella and salmonella.

Parasites
Where queens are not wormed, heavy kitten infestations can result in a poor body condition, soft or bloody stools, lack of appetite, a pot-bellied appearance, weight loss, and occasionally death. A severe flea, tick or hookworm infestation can result in significant anaemia. Gut parasites, such as Giardia, Tritrichomonas foetus, isospora or cryptosporidia may cause diarrhoea and a failure to thrive. Toxoplasma infection may result in abortion, stillbirths and fading kittens.

In general
Where specific infections keep recurring within a cattery it may be necessary to try to detect carrier animals. However, since a number of infections can cross between species, affecting both cats and dogs, and even humans, it may be necessary to look for carriers amongst pet dogs, or even the owners. This is true for many of the bacterial and protozoal gut infections (eg salmonella, campylobacter, Giardia and cryptosporidia), and can also occur with Bordetella bronchiseptica (which is one of the causes of ‘kennel cough’).