Dogs as a vector for illness
Large dogs can be very useful creatures post-collapse. A trained dog can pull a sled in winter. A dog can detect and scare a predator of multiple sizes. Many times, I've seen dogs act in intelligent and nurturing ways to protect weaker tribal members from copperheads and aggressive people. Dogs' sense of smell is far more acute, and so they will notice human odors as well as fire way before you detect it. They will hear sounds from far away. They will notice a change and alert you. PAY ATTENTION! They will communicate with you.
Most dogs are useless other than being companions post-collapse. I love dogs. They are wonderful creatures. Most people don't train their animals. This is odd since most dogs actually love to be trained and use their minds. They are naturally clever, but become dull and lifeless and fat because their owners think that they're human and treat them this way.
After coming inside from being outside, a dog will naturally groom themselves. It's important for you to check them carefully for ticks, especially deer ticks. These carry Lyme disease. Lyme disease eventually displays a bullshead pattern in most cases. The patient will exhibit declining cognition and lethargy and depression. It could be fatal post-collapse.
A bite from one can cause tick fever particularly if they bite around a human's head. It can causes paralysis. It's not something people are used to seeing. Good link by the way for detecting issues.
[link to www.merckvetmanual.com
The most likely issues of contagion from zoonotic means from dogs is worms. Dogs lick places that you don't want to think about. They roll in dead animals when those are present. They will eat carrion when hungry. You must be careful and watchful of your pets behavior.
[link to www.2ndchance.info
Tapeworms, hookworms, and pinworms are those ones were concerned with. Most humans by age four have had worms, but no one knew. After a collapse, this will be a very serious issue due to lack of hygiene. Diatomaceous earth that is edible is probably our best medicine here. They get heartworms but these are not typically transmitted in humans (still possible).
Giardia and toxoplasmosis gondii have previously been discussed as water bourne protozoa. Dogs can carry them, but usually cats carry the latter. Cryptosporidium is also an issue.
Dog fecal matter doesn't belong in the garden and I wouldn't compost it. Decaying dog fecal matter will seep into the ground and could contaminate a well. It definitely is a vector for the three protozoa based diseases above. It definitely will scare some small mammals away. If you smell it, it's NOT being dealt with properly and is a health risk.
All of the common bacteria responsible for skin infections and stomach flu can be carried by dogs. It most likely meant they drank bad water or ate raw meat or both.
Rabies is always an issue, especially after a collapse. Your dog may be current on vaccination, but remember that a lot of people won't do this, nor will they be able to feed their pets post-collapse, so feral dogs will be running around.
It's gruesome, but practical to realize that some people will eat dogs in such situations and they may easily become infected from improperly preparing or cooking them. The very same issues of handling meat and nicking digestive organs during butchering are the main issues.
If you love your dog, you'll rethink how to best train, feed, protect, and use preventative medication for your animal(s). They are wonderful companions and we want to protect them as our family members in SHTF scenario.
Note, it's entirely possible for a dog to carry equipment in a pack.
Think, a dog's coat is highly variable. If they're not covered up in Wintertime, then they certainly can get some infections, and some of these can be spread to humans. It's not unusual for a flu to jump species. Keep them warm and isolated if they exhibit flu-like symptoms.