Man and dog—a relationship that is nearly as old as time itself. Protector of our homes, pulling our sleds, finding missing people in rubble after an earthquake, dogs have been invaluable to the human race.

However, dogs are indeed animals and exposure to dogs has the potential for a plethora of infectious diseases. Here is a summary of possible diseases and routes of infection:

McNab dog Public domain image/Jezzabell
McNab dog
Public domain image/Jezzabell

Bites
Dogs have a diverse bacteriologic flora and many infections are polymicrobic in nature. Here are specific examples:

Pasteurella
Pasteurella infections if not treated in a timely fashion, can lead to cellulitis and can spread to cause serious systemic infection.

Capnocytophaga
It is for the most part considered an opportunistic pathogen, causing little problems with healthy individuals, usually causing the most severe disease in those with a predisposing condition; splenectomy, chronic alcohol abuse, or immune system problems (steroid therapy, blood malignancies and AIDS).

Splenectomized individuals are 30 to 200 times more prone to die from bacterial infections because the spleen produces cells that become antibody-producing cells. Also the spleen is integral is sending out macrophages (cells that engulf and destroy foreign substances like bacteria in the bloodstream).

The clinical illness is typically one of severe septicemia, shock and disseminated intravascular coagulation. Other manifestations of the disease include cellulitis, gangrene, meningitis and brain abscesses. The infection with Capnocytophaga carries a 27% chance of being fatal.

Rabies
Dogs that have rabies usually appear aggressive. Initially, like in many diseases, the symptoms are non-specific; fever, headache and malaise. This may last several days. At the site of the bite there may be some pain and discomfort. Symptoms then progress to more severe: confusion, delirium, abnormal behavior and hallucinations. If it gets this far, the disease is nearly 100% fatal.

Bacterial diarrheal diseases

Campylobacter
Campylobacter jejuni
is a cause of canine diarrhea. Studies have shown an association between humans and close contact with sick puppies.

Salmonella
Dogs can act as a reservoir for human infection. Canine salmonellosis usually consists of fever, vomiting and diarrhea. However, many dogs can shed the bacteria in their feces asymptomatically. People get infected the same way as with Campylobacter, fecal-oral route.

Parasitic diarrheal diseases

Giardia
Giardia can cause diarrhea in dogs and some studies have shown carrier prevalence in dogs of up to 25 percent.

Parasitic roundworm disease

Toxocara canis Life Cycle Image/CDC
Toxocara canis Life Cycle
Image/CDC

Toxocara
This parasite can be spread to humans by ingestions of eggs from the soil or from contaminated hands. Most at risk are young children under 5 years of age, especially those with a history of eating dirt and exposure to puppies.

Human infection with Toxocara usually takes one of two forms; visceral larval migrans (VLM), this is where the larvae migrate aimlessly. They usually end up migrating to the liver, but almost any tissue can be invaded.

The other more rare disease is ocular larval migrans (OLM), where the larvae enter the eye where permanent vision loss is possible

Related: Infections you can get from domestic cats

Superficial infections

Ringworm
The most common fungi of dogs to cause ringworm in humans is Microsporum canis. Up to 30 percent of human cases of ringworm in urban settings are estimated to be animal in origin.

Ectoparasites
Dogs can bring certain vectors into the house that can infect humans. Fleas and ticks that carryRocky Mountain Spotted Fever, the plague and lyme disease can bite and infect the human dog owner.

Canine scabies
Sarcoptic mange can be transmitted to humans, however most authors believe that the mites cannot complete their life cycle in humans. You’ll itch a bit then they’ll eventually die off.

This is merely a summary of potential infections you can get from your dog. There are many more to include leptospirosis and the tapeworm, Echinococcus. Of utmost importance, make sure you keep the animal’s rabies vaccinations up to date.

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