Prostatitis in dogs: prostate infection and treatment

Overview

The prostate lies behind the bladder and surrounds the urethra in the pelvic area. It has two lobes. The rectum runs above it. Because of this position, a painful prostate may also make passing faeces difficult.

Prostatitis is the second most common prostate disease in entire males. It can be acute, developing suddenly, or chronic and long-standing. The chronic form is more common. The forms differ in symptom progression and severity.

Among 82 dogs treated in referral care, 63% had acute and 37% chronic inflammation. These dogs had presented for prostatitis or a prostatic abscess.

Causes

Bacteria can reach the prostate through the bloodstream. Another route ascends from the urethra into the gland. Blood-borne infection is typical of the acute form. Ascending infection is more often associated with chronic disease.

Possible causes include Escherichia coli, staphylococci and streptococci, for example. Canine prostatitis usually involves pus-forming inflammation. Prostatitis without bacterial infection is extremely rare in dogs.

Chronic inflammation is often associated with benign prostatic hyperplasia. This is age-related prostate enlargement that is not cancer. It involves male hormone effects or an altered androgen-to-oestrogen ratio. Associated tissue changes may predispose to bacterial infection.

In hyperplasia, prostate cell numbers increase. Individual cells also become larger. Fluid-filled cysts can form within the gland.

Risk factors

Prostate problems can develop in sexually mature males of any age. However, symptoms occur more often in older males than young ones. Prostatitis is rare in castrated dogs.

Benign hyperplastic changes may begin as early as 2.5 years. Hyperplasia involving cysts becomes more common after 4 years of age. Median age in the 82 dogs treated for prostatitis or abscessation was 9 years. An infected prostatic cyst can also act as a bacterial reservoir.

Being near a bitch in season may bring out or worsen signs of benign enlargement.

Typical symptoms

Acute inflammation may make a dog clearly ill, while chronic disease causes few symptoms:

• Fever and general illness.

• Abdominal or perineal pain.

• Reduced appetite and lethargy.

• More frequent, difficult or bloody urination.

• Dribbling urine.

• Painful or difficult defaecation.

• Abnormal discharge from the urethral opening.

The source of prostate pain can be difficult to recognise. Recurrent urinary tract infection may be the only sign of chronic bacterial prostatitis.

Concurrent enlargement and chronic inflammation may also cause blood in semen or reduced fertility.

Complications and consequences

Acute inflammation can progress to a prostatic abscess. Several small pockets of pus may merge into a large abscess. Abscesses were found in 40% of the 82 dogs treated for prostatitis or abscessation.

Severe acute disease may involve dehydration and shock. Bacteria can also spread into the bloodstream. Prostate infection often occurs alongside urinary tract infection. Prostatic fluid normally flows back into the bladder too.

The outlook for bacterial prostatitis is generally good with appropriate antimicrobial treatment and castration.

In the 82 treated dogs, an abscess did not appear to indicate a poorer outlook.

Diagnosis at the vet

Palpation, blood and urine

The vet combines symptom history, clinical examination and laboratory findings. Rectal palpation assesses gland size, tenderness and symmetry. Rarely, size and shape may be normal despite inflammation.

A blood count may show increased neutrophils and inflammation-related cell changes. The inflammatory marker CRP may also rise. Urine may contain blood, inflammatory cells and bacteria. Urine culture includes testing bacterial antimicrobial susceptibility.

Blood biochemistry is also considered as part of a wider investigation.

An entire male is assessed for prostatitis if bacteria are found in urine or bacterial cystitis is present.

Ultrasound and prostate samples

Ultrasound assesses prostate size and internal structure. An inflamed gland may look uneven and contain small fluid pockets. The examination also looks for abscesses and changes consistent with a tumour.

X-rays may also help identify prostate enlargement.

Prostatic mineralisation was found in 20% of the 82 dogs treated for prostatitis or abscessation. Mineralisation therefore does not automatically mean prostate cancer.

Chronic inflammation can be investigated using the prostatic fraction of semen. Both cells and bacterial growth are examined. A male with chronic disease is often willing to provide a semen sample. In acute inflammation, however, pain may prevent collection this way.

A prostate sample can also be collected with an ultrasound-guided fine needle. A tissue sample may help investigate a concurrent tumour when needed. An acutely infected prostate must not be massaged to obtain a sample. Massage can release bacteria into the blood and cause severe systemic infection.

Sampling gland tissue directly has the advantage of less contamination by bacteria from elsewhere.

Urine and prostate bacterial cultures agreed in only 50% of the 82-dog case series. A prostate sample may therefore be needed even with a negative urine culture.

Prostatic fluid is not necessarily completely bacteria-free in a healthy dog. Bacteria may also enter the sample from the lower urinary tract during ejaculation or flushing. Even healthy canine prostatic fluid can contain 100,000 colony-forming units per millilitre.

Separate testing for Mycoplasma and Ureaplasma may be considered, but finding them is unusual. Infections caused by these bacteria are rare.

Considering brucellosis

Brucella canis can cause epididymitis and prostatitis in males. Screening for symptom-free infection relies mainly on antibody testing. Closely related bacteria may cause false-positive screening results.

Even minimal Brucella canis growth in culture is significant. However, a negative culture may be false even when a dog carries the bacterium.

Treatment

Antimicrobials and supportive care for acute disease

Bacterial prostatitis is treated with an antimicrobial prescribed by the vet. Selection is based on bacterial susceptibility. A severely dehydrated dog or one in shock needs intravenous fluids. Pain relief is part of maintaining comfort and wellbeing.

A tissue barrier limiting transfer from blood into the prostate makes it difficult for many drugs to reach the infection. The barrier may remain functional particularly in chronic disease. The medicine must therefore reach an adequate concentration within the prostate itself. Blood rather than urinary susceptibility breakpoints are used when interpreting results.

Among cultures from dogs with prostatitis, 29% were resistant to one antimicrobial. Resistance to at least two drugs occurred in 52%. Clindamycin and macrolides, for example, are unsuitable as empirical choices against the usual Gram-negative causes.

Abscesses and concurrent enlargement

Large prostatic abscesses are usually drained surgically. The omentum, a fatty sheet within the abdomen, can be used to manage the drained cavity. In some circumstances, an abscess can also be drained through the skin under ultrasound guidance. Success is less certain with medication alone.

Concurrent benign enlargement also needs treatment in chronic inflammation. Antimicrobials alone do not usually resolve this combined problem. Castration is considered once infection has settled. It reduces the size of a benignly enlarged prostate.

Enlargement can also be managed with medicines targeting hormonal effects. These options work less well when the gland contains cysts or abscesses. Castration itself does not change the choice of antimicrobial needed. A need to preserve breeding ability also affects treatment selection.

Finasteride can treat enlargement while maintaining normal testosterone. Treatment has not been found to reduce semen quality, fertility or libido. In contrast, sperm production and fertility stop while a GnRH agonist implant is active.

Confirming treatment response

Repeat culture of urine or prostatic fluid is recommended 2–4 weeks after antimicrobial treatment ends. Prostate size and structure can be checked by ultrasound 8–12 weeks after treatment when needed. Semen quality improves in most dogs as bacterial inflammation settles.

Routine urine or prostatic fluid cultures during treatment are not recommended.

A poor initial response prompts reassessment of diagnosis and treatment. Further investigations may include another tissue or fluid sample for culture and cytology. Prostate size is monitored alongside clinical wellbeing.

Prevention

Castration is recommended for a male with bacterial prostatitis that is not intended for breeding. Managing concurrent benign enlargement is part of resolving chronic inflammation. Some national guidance recommends Brucella canis antibody testing for imported dogs and dogs from abroad used for breeding.

An infected male can spread the bacterium particularly during mating. Large numbers of bacteria may be shed in semen. Brucellosis can also infect people.

A dog with confirmed brucellosis should avoid contact with other dogs.

Important for dog owners

Record fever, appetite, pain-related behaviour and urination frequency. Note whether blood is in the urine or discharge also appears from the urethral opening between urinations. Mention previous urinary infections, castration, hormonal treatment and antimicrobials used. Explain whether your dog was imported or has mated with dogs from abroad too.

Ask which sample will establish the bacteria's location and susceptibility. Arrange follow-up samples and any ultrasound at the start of treatment. Ask what to do if pain, fever or difficulty urinating returns. If breeding is planned, discuss both semen testing and how enlargement treatment affects reproductive ability.

Culturing Brucella canis poses an occupational safety risk to laboratory staff.

Frequently asked questions

Can my dog have prostatitis without a fever?

Chronic bacterial prostatitis can cause very few symptoms. Recurrent urinary tract infections may be the only sign. Acute disease, however, usually involves illness, abdominal pain and fever. Rarely, gland size and shape may also be normal despite inflammation.

Is a urine sample enough for diagnosis?

Urine culture is an important part of the investigation. However, urine and prostate bacterial findings may differ. If prostatitis is strongly suspected but urine culture is negative, a sample from the gland itself may be needed. Sampling method depends partly on the dog's pain.

Is prostatitis the same as an enlarged prostate?

Benign hyperplasia is age-related enlargement that is not cancer. Canine prostatitis is usually caused by bacteria. The two can occur together, as chronic inflammation is often associated with enlargement. Treating enlargement then also forms part of managing inflammation.

Does a prostatic abscess need surgery?

Large abscesses are usually drained surgically. In some situations, ultrasound-guided needle drainage through the skin is possible. A response to medication alone is less certain. Treatment also considers concurrent benign enlargement. Castration may additionally be considered once infection has settled.

Can prostatitis spread to people or another dog?

Brucella canis is one possible cause of prostatitis. It can pass from dogs to people. An infected male spreads it particularly during mating. Transmission to animals or people does not occur readily during brief contact.