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We can prevent parvovirus disease!

The best way to prevent parvoviral diseases is through vaccination, but it may be tricky due to the persistence of maternal antibodies.
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In this step we will be talking about how to control parvovirosis, both in dogs and in cats, using vaccines. One of the most difficult problems that the veterinarian must solve is to determine when to vaccinate puppies or kittens, because if there are residual antibodies transferred from the mother to the offspring, they may interfere with vaccination in these young animals.
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There are two main types of vaccines: dead or inactivated and live or attenuated. In a modified-live or live-attenuated vaccine, the causative virus has been weakened or altered so that it is no longer harmful or virulent, but is still capable of stimulating protective immunity when injected or otherwise administered. Viruses included in live-attenuated vaccines are excreted in faeces. This may be beneficial, because other animals might get vaccinated indirectly, or harmful because the attenuated vaccine might have regained virulence and may start an outbreak.
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On the other hand, inactivated vaccines are safer 00:01:24.540 –> 00:01:26.540 but less immunogenic.
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For dogs, only live-attenuated vaccines are available containing either the CPV-2 or CPV-2a strains. For puppies live-attenuated vaccines with higher titre have been developed and we will explore their interest later. For cats, most vaccines used are live-attenuated and derived from feline parvovirus or panleukopenia strains, although inactivated vaccines are also available. Newborn animals have not yet had a chance to make their own immunity, but they need protection against infections present in their environment. They receive immunity from their mother in the form of maternal antibodies. A very small part of this “passive immunity” is transferred across the placenta while the pup is still in the uterus, but they receive most of the protection with the first milk or colostrum.
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This maternal passive immunity is only temporary. It declines steadily over the first few weeks of life and is largely gone by twelve weeks. The maternal antibodies protect against diseases, but also recognize the vaccine antigens and inhibit the immune reaction against the vaccine. When the level of maternal antibodies declines, they no longer protect against the disease but are still in sufficient amount to inhibit the response to the vaccine. This period of time is called “susceptibility window”. For each puppy, the susceptibility window is different, depending of many factors. For example, in the case of puppy A, its susceptibility window is between 6 and 8 weeks old, while for puppy B, it is between 8 and 10 weeks old.
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In general, for all puppies 12 weeks-old and older, the level of maternal antibodies is too low to inhibit vaccination and puppies respond adequately to vaccination. But if we wait till puppies are 12 weeks old, they could become sick during the period of the susceptibility window. So, what is the recommendation? In order to vaccinate puppies, avoiding the inhibition produced by the presence of maternal antibodies, high titre attenuated-live vaccines against canine parvovirus have been developed for puppies. As its name suggests, the titre of vaccine antigens is higher in such vaccines than in the classical ones. In consequence, a larger amount of maternal antibodies is necessary to inactivate such vaccines in comparison with classical vaccines.
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The threshold of vaccine inhibition is higher, and the susceptibility window is shorter, as shown for puppy B. In a practical view, with high titre vaccines it is possible to vaccinate efficiently where classical vaccines fail as a result of the susceptibility window. High titre vaccines do not exist for feline panleukopenia or parvovirosis. Vaccination guidelines recommend to start canine parvovirus and feline panleukopenia vaccination at 8 weeks-old and to re-vaccinate again four weeks later. In case of animals living in rescue centres or in high-density communities, a third booster vaccination is recommended at 4 months-old. Every animal should receive a booster vaccination one year later. FPV and CPV vaccination has been shown to maintain a solid immunity for many years.
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Subsequent revaccinations could be given at intervals of 3 years, depending on the manufacturer’ instructions. Vaccination of pregnant queens or kittens younger than 4 weeks of age is highly unrecommendable. The live attenuated vaccine is able to cross the placenta and may induce either stillbirth or the birth of kittens with ataxia. What an informative activity, don’t you agree? We have understood how vaccines work and why very young animals may not be vaccinated adequately. What we learnt about maternal immunity and the susceptibility window is also valid for other diseases and animals.
We have seen that maternal antibodies may interfere with vaccination, because they “envelope” the antigen in the vaccine and don’t allow it to start an immune response.

Task

Consider and add your thoughts on the following questions:
  • Does this surprise you?
  • Have you ever observed a vaccine administered to young animals that was not effective?
  • How do you think that maternal antibodies reach the young animal? Is it the same in all species?
  • Check vaccination protocols and reflect on which vaccines animals may require revaccination for.
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Animal Viruses: Their Transmission and the Diseases They Produce

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