How Parvo infection happens

Continued from last week…

Last week, we dealt with some questions about Parvo virus infections, like:

Where does the virus come from?

Why only puppies are infected most of the time?

Natural protection against the virus.

Today, let us look at other aspects of Parvo infection like:{{more}}

Incubation

The virus enters the body through the mouth as the puppy cleans itself or eats food off the ground or floor, or drinks contaminated water. A minuscule amount of infected stool is all it takes. There is a three to seven-day incubation period before the puppy seems obviously ill.

Upon entering the body, the virus seeks out the nearest rapidly dividing group of cells. The lymph nodes in the throat fit the bill and the virus sets up here first and replicates to large numbers. After a couple of days, so much virus has been produced that significant amounts of it have been released into the bloodstream. Over the next three to four days, the virus seeks new organs containing the rapidly dividing cells it needs: the bone marrow and the delicate intestinal cells.

Within the bone marrow, the virus is responsible for destruction of young cells of the immune system. By killing these cells, it knocks out the body’s best defense and ensures itself a reign of terror in the Gastro Intestinal (GI) tract where its most devastating effects occur. All parvoviral infections are characterized by a drop in white blood cell count, due to the bone marrow infection. Seeing this on a blood test may help clinch the diagnosis of parvoviral infection.

The GI tract is where the heaviest damage occurs. The normal intestine possesses little finger-like protrusions called villi. Having these tiny fingers greatly increases the surface area available for the absorption of fluid and nutrients. To make the surface area available for absorption greater still, the villi possess microvilli, which are microscopic protrusions. The cells of the villi are relatively short-lived and are readily replaced by new cells. The source of the new cells is the rapidly dividing area at the foot of the villi called the crypts of Lieberkuhn. Parvovirus strikes right at the crypt.

Without new cells coming from the crypt, the villus becomes blunted and unable to absorb nutrients. Diarrhea in large quantities results, not to mention nausea. The barrier separating the digestive bacteria from the bloodstream breaks down. The diarrhea becomes bloody and bacteria can enter the body, causing widespread infection (remember that that virus has also simultaneously destroyed the bone marrow’s ability to respond immunologically).

The virus kills one of two ways:

• Diarrhea and vomiting lead to extreme fluid loss and dehydration until shock and death result.

• Loss of the intestinal barrier allows bacterial invasion of potentially the entire body. Septic toxins from these bacteria result in death.

How is survival possible?

Even parvovirus cannot disrupt the entire immune system. Plus, every day that goes by allows more antibodies to be produced. This antibody can bind and inactivate the virus. Whether survival is possible amounts to a race between the damaged immune system trying to recover and respond versus the fluid loss and bacterial invasion.

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