Giardia are single-celled organisms, infectious to many types of animals (including humans) that stick to their host’s intestinal tract for feeding.
It has 2 forms: one that lives in the environment (cysts) and one that lives within the host (trophozoite).
Transmission is by the fecal-oral route from infected stool or contaminated water.
After infection, it takes 5 to 12 days for dogs or 5 to 16 days for cats for Giardia to be found in the stool.
Giardia causes diarrhea ranging from minor to severe.
Treatment includes dewormers (Panacur) and Metronidazole (antibiotic).
A low-residue, highly digestible diet may be beneficial until stools are firm.
Because infective cysts can stick to fur, patients should be bathed frequently during and at the end of treatment.
Giardia can be killed with common disinfectants.

Leptospira organisms are spiral-shaped bacteria called spirochetes that can infect many types of animals (including humans).
Leptospires live best in warm, slow-moving water, such as after heavy rains or flooding. After the water clears, they contaminate the soil for many months. Wildlife are common carriers of infection
Dogs become infected by leptospires when irritated or cut skin comes into contact with infected urine or water contaminated with infected urine. Alternatively, bite wounds, exposure to reproductive secretions, and even eating infected tissues can transmit this infection.
The organisms quickly spread through the bloodstream, leading first to inflaming the blood vessels: fever, abnormal bleeding, abnormal bruising, and tissue edema appear after an approximately seven-day incubation period.
By two weeks post-infection, the leptospires have set up shop in the kidneys, where they continue to generate inflammation, pain, and potentially total kidney failure and the inability to produce urine. Some serovars also go to the liver and generate inflammation there, though the liver disease is generally not as severe as that of the kidney.
Leptospira interrogans sensu lato is sensitive to doxycycline, a readily available antibiotic.
Intravenous fluids are crucial to support blood flow through the damaged kidneys so that recovery is possible.

Canine heartworms, Dirofilaria immitis, are parasitic worms that pose a serious threat to dogs.
These long, slender worms live in the pulmonary arteries (and, occasionally, within the heart) of dogs and can measure up to a foot in length.
They can cause substantial damage to the lungs and heart.
Adult heartworms cause inflammation of the blood vessels in the lungs, resulting in respiratory issues and pulmonary hypertension. In some cases, this leads to weight loss, weakness, right-sided congestive heart failure, reduced quality of life, and even death.
Mosquitos are vectors of heartworm disease.
Preventing heartworms is much easier (especially for your dog) than having to treat an active heartworm infection.
Learn more at: https://www.heartwormsociety.org/pet-owner-resources/heartworm-basics