Dogs are infected with a type of virus called Canine parvovirus and the dogs which are ill from this disease are called “parvo” Moslty those dogs and puppies are at high risk which are younger than 4 months of age.

Cause
The disease is spread through contact to infected dog, contaminated feces, people or environment. The disease can also be spread through contaminated food and water bowls, , collars, leashes, hairs and feet of dogs, contaminated cages, hands and clothing of people who handle infected dog. The worst part is that the virus can survive in dry, hot, cold and even humid environment for longer period of time and a minute amount of infected feeces can infect the healthy dog that comes near to it.
The virus called canine parvovirus type 2(CPV) was first emerged in 1976 among the dogs of Europe which turned into worldwide epidemic of myocarditis and gastrointenstinal inflammation (gastroenteriris) by 1978 due to its unchecked spread. Now it is understood that the virus not only affect dogs but also attack coyotes, volves, foxes, skunk and racoons.
The family of this virus is closely related to panleukopenia virus (FPV) which was known to infect cats and minks since 1920

Symptoms of Parvo in Puppies
Canine parvovirus (CPV) is a highly contagious virus that affects dogs. When a dog is infected, the virus attacks the cells in the lining of the gastrointestinal tract, causing severe inflammation and damage. This leads to a variety of symptoms, including:
• Diarrhea: This is often the first symptom and can be severe, often containing blood.
• Vomiting: Dogs with CPV may also experience frequent vomiting.
• Loss of appetite: Many dogs with CPV will lose their appetite and refuse to eat.
• Dehydration: Due to diarrhea, vomiting, and loss of appetite, dogs with CPV are at risk of becoming dehydrated.
• Lethargy: Dogs with CPV often become weak and tired.
• Fever: Many dogs with CPV will develop a fever.
• Weight loss: In severe cases, dogs can lose a significant amount of weight.
The severity of symptoms can vary from dog to dog and depends on many factors, including the dog's age, breed, and overall health. Puppies and young dogs are often more severely affected than adult dogs.
It's important to note that CPV can be fatal if left untreated, so it's important to seek immediate veterinary care if you suspect your dog has been infected.
After the onset of clinical signs, most deaths from parvovirus occur within 48 to 72 hours. If your puppy or dog shows any of these signs, you should contact your veterinarian immediately.

What happens during infection?
Canine parvovirus (CPV) is a highly contagious virus that primarily affects dogs. The mechanism of action of CPV is as follows:
1. The virus enters the body through the mouth and nose, where it attaches to cells in the lining of the gastrointestinal tract.
2. Once inside the cells, the virus replicates and releases new viral particles, which can infect other cells.
3. As the virus replicates, it causes damage to the cells in the lining of the gastrointestinal tract, leading to inflammation and tissue destruction.
4. This inflammation and tissue destruction can lead to diarrhea, vomiting, and other symptoms of CPV.
5. In severe cases, the virus can also attack other organs, including the heart and the bones.
6. The viral replication and cell damage can also cause the immune system to respond and release substances that can cause damage to the host's body, leading to a severe inflammatory process.

Diagnosis

The presence of canine parovovirus can be tested with:
• fecal ELISA test (enzyme linked immunosorbent assay) to detect the presence of parvovirus proteins
• PCR test of fecal samples to detect the presence of viral DNA
• Blood cell count (the parvovirus infects is the bone marrow, a low white blood cell count can be suggestive of CPV infection.)
• If a dog has both a positive ELISA reading and a low white blood cell count, a fairly confident diagnosis of CPV may be made.
Treatment
The treatment option for dog vary depending on severity of dog’s sickness.
It mostly involves the supportive care and management of symptoms.
A stay in hospital is necessary for dog so that intravenous fluid could be provided as a dog could loss a lot of nutrients from the body due to vomiting and diarrhea. Intravenous fluid is preferred because the virus affect gastrointestinal tract and it can’t tolerate of absorb the important nutrients.
The low blood count caused due to affected bone marrow, can be boost by blood transfusion.
Anitibiotics are also administrated either through injections of intravenously if the intestinal bacteria entered in blood stream.
Medications are also advised to control nausea, vomiting and diarrhea.
Most of the dogs are recovered from the infection if the recovery was started on time and also develop life long immunity against the specific virus.