Most of us know that spaying and neutering help prevent unwanted litters. But did you know these simple surgeries also protect pets from some dangerous diseases?

Certain infections in cats and dogs spread through fighting, biting, and mating—and those behaviors are all driven by hormones. By reducing those hormones, spay and neuter surgeries don’t just stop overpopulation—they stop the spread of disease too.

Let’s look at some of the most common illnesses that can be passed between pets and how sterilization quietly keeps them safer.

For Cats: FIV and FeLV — Two Serious Viral Threats

Feline Immunodeficiency Virus (FIV)

FIV weakens a cat’s immune system, making it hard for them to fight off infections. It spreads mainly through bites and scratches, but because it’s found in saliva, blood, and other body fluids, it can also spread through mating or other close contact.

Unneutered male cats are especially at risk since they’re more likely to roam, fight, and bite other cats. Once infected, cats may seem fine at first, but the virus can slowly damage their immune system over time, leaving them vulnerable to other illnesses.

Spaying and neutering help stop the behaviors that lead to FIV transmission—less roaming, fewer fights, and no mating. That means fewer chances for the virus to spread from cat to cat.

Feline Leukemia Virus (FeLV)

FeLV is another virus that spreads through saliva, blood, and other body fluids like milk or urine. It can pass between cats during grooming, fighting, sharing food bowls, or mating. Once infected, cats may develop anemia, infections, or even cancer. Sadly, many don’t survive long after showing signs of illness.

Because FeLV spreads through close and repeated contact, cats that live outdoors or in multi-cat settings are at the highest risk. Spaying and neutering reduce that risk by calming territorial instincts, limiting roaming, and stopping the drive to mate—all of which help prevent contact with infected animals.

In short, sterilized cats are less likely to fight or seek out partners, which means fewer bites, fewer matings, and fewer ways for viruses like FIV and FeLV to spread.

For Dogs: Infections That Hide Behind Breeding and Biting

Dogs face their own set of diseases that can spread through contact, especially during mating or fights. Here are a few of the most concerning:

Canine Brucellosis

This bacterial infection spreads through mating and reproductive fluids. It can cause infertility, miscarriages, and long-term illness in both male and female dogs. There’s no easy cure, and infected dogs can silently spread it for years.
Spaying and neutering are the best defenses—by preventing breeding altogether, they stop the main way this disease travels.

Canine Herpesvirus

This virus can cause devastating illness in newborn puppies and reproductive problems in adult dogs. It spreads through genital and oral secretions, which means it can pass during mating or close contact between dogs.
Sterilized dogs are far less likely to transmit or catch the virus because they don’t engage in mating behaviors that spread it.

Canine Transmissible Venereal Tumor (CTVT)

CTVT is a rare but fascinating—and frightening—disease. It’s actually a contagious cancer that spreads when tumor cells transfer from one dog to another, usually during mating or licking the affected area.
Once again, spaying and neutering stop the behavior that makes this disease possible.

Why Spay and Neuter Matter Beyond Birth Control

Spay and neuter surgeries protect pets in so many quiet, important ways:

Less Fighting = Fewer Injuries
Neutered animals are calmer and less territorial, which means fewer bites and scratches where infections can spread.
No Mating = No Sexual Transmission
Many diseases—including FIV, FeLV, and several canine infections—can be spread during mating.
Less Roaming = Fewer Risky Encounters
Pets who stay close to home are less likely to meet infected animals or get into fights.
Healthier Communities
When fewer animals are fighting, breeding, or spreading illness, the whole community becomes safer for pets—both owned and homeless.

The Bigger Picture

When we spay and neuter, we’re doing far more than preventing litters. We’re breaking the cycle of suffering caused by disease, injury, and overpopulation. Every surgery means fewer animals living in pain or passing on infections that can devastate entire colonies or neighborhoods.

At PennyFix, we believe prevention is compassion in action. By helping fund spay and neuter programs, we’re not just saving lives today—we’re building a healthier, kinder tomorrow for dogs and cats everywhere.

A Final Word

Every pet is unique, and every decision about their care should be made with a trusted veterinarian. Your vet can guide you on the best time for surgery, testing, and vaccinations to keep your furry family members safe.

Together, through education, compassion, and prevention, we can give every animal the healthy, loving life they deserve.

More than birth control: The lifesaving power of spay & neuter