How parvo works


Parvo, caused by the Canine Parvovirus (CPV) is a severe, potentially fatal disease affecting dogs. It is particularly dangerous for puppies. It is important to understand how this virus works so that you know what’s happening in your pup’s body and can understand how it is treated.

  • The dog or puppy comes into contact with the virus. Not all dogs will be infected but, if they are, the incubation period is around 3 – 7 days (but can be as little as 2 days or as long as 2 weeks). An infected dog is contagious for around 6 weeks after symptoms first appear. 
  • The  virus attacks the neck lymph nodes and tonsils, where it invades lymphocytes (one of the body’s main types of immune cells). You may feel ‘swollen glands’ in an infected dog. 
  • Next, the virus creates copies of itself inside the lymphocytes, which enter the bloodstream, transporting the virus throughout the body. Many of the infected lymphocytes are killed by the body’s defences, which is why a blood test will show reduced lymphocytes. 
  • The virus needs rapidly dividing cells in order to multiply. It particularly likes the cells of the bone marrow and the lining of the small intestine. In young pups, it can also target the heart (cardiac parvo). 
  • Bone marrow is needed to produce immune cells. Because this has been invaded by the virus, the body cannot mount a proper response to the virus and a vicious cycle develops – the worse it gets, the less the body can fight, so the virus gets a stronger hold.
    This also makes it even easier for the CPV to invade in the intestine… 
  • …where it starts to cause severe damage to the intestines’ epithelial lining, which is needed for nutrient absorption, prevention of excessive fluid loss into the stool, and protection against bacterial invasion. 
  • Villi – tiny fingerlike projections lining the intestine – are damaged and blunted so that they can’t absorb nutrients properly anymore. 
  • The virus invades the areas where the new epithelial cells are made so that the body now can’t even fix what the virus has damaged. 
  • The intestinal surface is now severely damaged and there is a lot of inflammation so you can imagine how painful it must be. 
  • Nutrients can’t be absorbed, making it even harder for your pup’s immune system to mount a defence.
    More and more fluid is lost into the stool (hence watery/loose stools).
    There is no protection against opportunistic bacterial or fungal infections from moving into the body from the bowels.
    Your pup will by now be feeling extremely sick and will likely vomit and have a very runny tummy. 
  • The damaged intestinal lining starts to slough off, and you may see blood in the stool. It is the necrosis and sloughed-off lining which causes the distinctively putrid sickly-sweet ‘parvo poop’ smell. 
  • They will be losing a lot of fluid by now so the diarrhoea will be very runny and dehydration is a big risk. This can cause sunken eyes, non-elastic skin, pale gums, and collapse. Your pup may be placed on a drip or have sub-cutaneous fluids adminstered. 
  • Blood and protein leak into the intestines, so the infected pup loses even more in the stool, further weakening and dehydrating them. This adds to the smell and colour. 
  • All animals have bacteria, both good and bad, living in the intestines but they are usually kept under control by the immune system and prevented from leaving the intestine by the lining. Now, these bacteria flood through into the bloodstream and, because the immune system has been damaged, it can’t fight these invading bacteria. Sepsis can follow. This is why vets will often prescribe antibiotics for parvo-affected puppies – not to try and treat the virus (antibiotics do not kil viruses) but to fight these opportunistic bacteria. 
  • Parvo is not always fatal but when it is, the cause of death is shock, dehydration, sepsis from intestinal bacteria entering the blood stream, or a combination of these.

Now that you understand how the damage is done by parvo, you will see why quick, aggressive supportive treatment is so important, and that, if your pup survives, you will have some work to do to help them recover. You can also see why these so-called ‘boereraad’ DIY treatments will not work.

Know that treating parvo properly and in a way that minimises suffering is intensive and extremely expensive – in the tens of thousands of Rands. If you do not treat it swiftly (i.e. as soon as symptoms start), you have a low success rate and your pup will suffer a great deal. As you can imagine, the above is very painful and stressful; this illness causes a huge amount of suffering. Vaccinations and taking proper precautions are infinitely cheaper, easier, and less risky.

A final note about ‘leaving your puppy to die peacefully at home’ (rather than treating or euthenising). Let’s be clear: if you do not treat parvo, the death will be anything but peaceful. And you will be exposing even more dogs to the same suffering. If the right treatment is unaffordable or inaccessible, putting the dog or puppy to sleep IS the kindest thing to do.


There is a cardiac form of parvo which occurs in puppies under 8 weeks of age. It is almost always fatal. It may be accompanied by the intestinal symptoms but usually not. Puppies with cardiac parvo may die very suddenly, or they show signs of heart failure, including shortness of breath, rapid and labourered breathing, swollen abdomen, and frothy fluid in the lungs. If they recover, which is rare, they will likely have chronic circulatory and heart problems. If a puppy has developed this, it is kinder to put them to sleep as soon as possible.

© Copyright reserved Jennifer Davies 2021

You may also like...