I had an advice call recently about the risk of hepatitis C transmission by cat scratches. Hepatitis C is a human virus that can cause serious liver disease. It is most commonly transmitted via the blood of infected individuals. The concern with cats in this case was whether there is a risk of transmission if a cat were to scratch someone with hepatitis C and then scratch someone else.
There are no reported cases of hepatitis C transmission via a cat scratch. For transmission to occur, the following must happen:
- The cat must scratch an infected person who has hepatitis C virus circulating in their bloodstream.
- The scratch must draw blood, which then contaminates the cat's claws.
- The virus must survive on the cat's claws.
- The cat must scratch someone else deep enough to draw blood.
- Hepatitis C virus must go from the cat's claws into the person's bloodstream and survive.
The odds of this sequence happening are very low. It's similar to the concerns about HIV transmission from dog bites - theoretically possible, never proven, and probably of very little concern.
This could be seen as similar to the situation with needlestick injuries in people: someone draws blood from an infected person, and then promptly sticks his or her finger with the needle by accident. Hepatitis C is not efficiently transmitted by needlesticks; only about 1.8% of people that get stuck in this manner (with a needle contaminated with blood from a hepatitis C-positive individual) develop antibodies against the virus. The risk is highest with hollow-bore needles (such as those used for injections and blood sampling) compared to needles used for sutures, because of the greater volume of blood that could be transferred via a hollow-bore needle. Cat scratches are presumably more like surgical needle punctures - there can only be contaminated blood on the outside of the claw, not inside it.
The only time I might have any concern would be if I suffered a significant scratch injury from a cat that had immediately before that caused a major injury in a hepatitis C-positive individual, such as in a situation that might be encountered when two people were breaking up a cat fight, or when someone was trying to pry an attacking cat off another person. It's a very unlikely scenario, and the associated risk would still be extremely low.
Bottom line: Don't worry about hepatitis C when around cats and infected people. Use common sense measures to avoid being scratched at all times.
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