Diskospondylitis is a bacterial or fungal infection of the disks between the vertebrae (intervertebral disks). This infection can occur in any area of the spinal column, and it can occur at multiple sites. Diskospondylitis is also known as spondylitis, intervertebral disk infection, and vertebral osteomyelitis.

Diskospondylitis occurs much more often in dogs than in cats.

The bacterial/fungal infection can reach the intervertebral disks several ways.

• Through the bloodstream, which is the most common method. (Chronic infections of the skin, urinary tract, prostate, etc. can result in bacteria entering the bloodstream and travelling to the disk area.)
  
• Via direct contamination from punctures or bite wounds near the spine, or from procedures or surgery near the spine.
  
• From the migration of foreign bodies through the area near the spine.

Signs

Neurological signs have a gradual onset and are progressive. At the beginning, spinal pain, stiffness, unsteady walking, and other nervous system problems may occur. Spinal pain is the most consistent clinical sign. Impaired movement (paresis) is usually mild, unless the infection gets into the spinal canal. However, if the pet doesn’t get appropriate treatment, signs can progress to paralysis, often caused by fractures of the vertebrae. The muscles alongside the spine may atrophy (waste away); this is most likely due to local nerve damage or associated myositis (muscle inflammation).

Spinal cord compression can be caused by granulation tissue, bony changes, or fractures or dislocations (luxations) due to the infection. The vertebral fractures or dislocations may require surgery to stabilize them.

Occasionally, the infection may result in meningitis, meningomyelitis, or an abscess in the spinal canal.

Diagnosis

Diagnosis may require radiography, advanced imaging modalities (CT scan, MRI, bone scintigraphy), urinalysis, bacterial cultures, serology, and cerebrospinal fluid analysis.

Radiography

Radiographs (X-rays) of the spine will typically show damage to the vertebrae on either side of the affected disks.  In chronic cases, bone changes and deformities of the spine may be seen. Changes may not show up on the radiographs for 3-6 weeks after clinical signs start, so if the first radiographs are normal but the clinical signs are progressing, your veterinarian will likely repeat the radiographs.

If a typical lesion is detected, radiographs of the entire spine are recommended because some pets have multiple lesions. Infection causes disk degeneration, and destroys the ends of the adjacent vertebrae. These degenerative changes may weaken the vertebral column and make it susceptible to pathologic fractures, which stem from infection rather than trauma. The body may try to bridge the damaged area with bone, which can encroach on the spinal cord and nerve roots, causing more problems.

Advanced Imaging

Bone scintigraphy, computed tomography (CT), and magnetic resonance imaging (MRI) are more sensitive than plain radiography, particularly for early lesions. Myelography and/or MRI/CT are helpful for pets that have neurological problems, and these imaging methods are considered important if spinal surgery is going to be done.

Urinalysis

Pets may have pus and/or bacteria in their urine.

Bacterial Cultures

Culturing the urine, blood, spinal fluid, or other infected tissues may help identify the organism(s) that caused the infection. However, culture of the infected disk space will yield the most accurate results. Fluoroscopic-guided fine needle aspiration may be necessary to get the best sample. If spinal surgery is necessary, samples of the infected areas should be obtained and cultured.

Serology

Brucellosis serology (checking the blood for current and previous infections) should be performed. Brucellosis is a possible cause of diskospondylitis, and can be transmitted to people.

Cerebrospinal Fluid (CSF) Analysis

CSF analysis is called for in animals with neurologic signs. In addition to culturing the CSF, routine cytology, cell count, and protein determination are done.

Causes

Bacteria

Bacteria such as Staphylococcus, Streptococcus, Escherichia coli, and Brucella spp. are commonly isolated organisms. Pseudomonas, Proteus, Pasteurella, Corynebacterium, and Actinomyces spp. are sometimes found. Reproductive problems may occur with Brucella infections. There are reports of pets infected with Bordetella spp., Erysipelothrix rhusiopathiae, and Salmonella spp.

Fungi

Fungal organisms that can cause diskospondylitis include Aspergillus, Blastomyces, Histoplasma, Coccidioides spp., and occasionally Paceilomyces. In Europe, infection with Rasamsonia argillacea has been reported. A single case of infection with Westerdykella spp. has also been reported in a German shepherd dog. Fungal infections can be more difficult to diagnose than bacterial infections, so your veterinarian will also look for enlarged lymph nodes, lung or eye lesions, and fungal organisms in the urine.

Other Agents

Protothecosis, a disease caused by a type of green alga, has been associated with diskospondylitis.

Treatment/Management/Prevention

Antibiotic Therapy

Treatment involves a long course of antibiotics that are specific for the infective organism. Ideally, the antibiotic selection will be based on culture and sensitivity results from the infected disk. If disk culture is not possible, then antibiotic selection will be based upon the culture results of urine, blood, or other infected areas.

Antibiotic treatment may be needed for many months. Recurrence of the disease or persistence of signs can be a problem if antibiotic therapy is stopped too soon, if the antibiotic being used is ineffective, or if corticosteroids or other immunosuppressive drugs are used. If clinical signs do not improve while the pet is taking antibiotics, your veterinarian may decide to repeat the disk culture.

As for Brucella infections, treatment is only undertaken with the understanding that a cure cannot be expected, long-term antimicrobials will be required, and the return of the infection is common. Infected dogs should be neutered to reduce the risk of transmission to other dogs and people, to remove potential reservoirs of infection, and to resolve other clinical problems (infection of the testicles, for example). For all practical purposes, Brucella diskospondylitis should be considered incurable.

Antifungal Therapy

Antifungal drugs, particularly itraconazole, may be effective for treating some cases of fungal diskospondylitis.

Decompression

Your veterinarian may advise surgical exploration of a lesion that does not respond to treatment or that has persistent draining tracts that suggest foreign body migration is occurring. Decompressive surgery and/or stabilization may be considered if evidence of spinal cord compression is found on myelography or MRI, or if severe, progressive neurologic problems occur. Surgical stabilization of affected sites may be useful in cases in which spinal instability is a significant complication.

Supportive Therapy

If antibiotics are effective, pain medications may be needed for only a few days.

Monitoring and Prognosis

After your pet has had at least six weeks of therapy, your veterinarian may take more radiographs to see if the lesions have improved. Improvement of clinical signs often occurs before improvement can be seen on the radiographs. Prognosis for recovery is guarded and depends, to some degree, on the cause of the diskospondylitis.

Brucellosis is an important venereal disease in many species. It does not usually come up in pet ownership because most pet dogs are not bred. Once someone decides to breed their dog, though, they should know all about this disease, particularly since it can be transmitted to humans.

Other Brucella species are Brucella ovis, which affects only rams, Brucella neotomae, which affects desert mice, Brucella microti which affects rodents and voles, Brucella ceti and Brucella pinnipedialis, which affect marine mammals, and Brucella inopinata, which has only been found once in a human breast implant infection. Luckily for people, Brucella canis causes much less serious disease in humans than the livestock Brucella but the health department still considers any Brucella infection reportable.

How Dogs get Infected

Dogs like to stick their noses in all sorts of nasty places. They also chew up all sorts of disgusting things. Brucellosis can be contracted sexually, but it can also be contracted by inhalation (sniffing contaminated urine or fetal membranes), through the eyes, or orally (licking contaminated urine or urogenital secretions or chewing up fetal membranes). Urine and saliva from an infected dog are not nearly as rife with organisms as urogenital secretions; it is when breeding and/or whelping is in the picture that the transmission risk becomes high.

When a female dog aborts a pregnancy because of a Brucella infection, she continues to secrete fluids packed with Brucella bacteria for four to six weeks.

Brucella organisms are able to survive in the environment for months if conditions are moist, cool, and dark. Bleach is an effective disinfectant in the environment.

What Happens After Infection?

The organism requires three weeks on average to become evident in the bloodstream. After that, it localizes in the reproductive or urinary tract and either continuously or periodically seeds the bloodstream from there. Lymph nodes can enlarge and possibly the spleen or liver can become inflamed but generally the infected adult dog does not seem sick in the short term. Chronic disease from long-term immune stimulation can result. Diseases produced by long-term inflammation can include:

• Diskospondylitis (inflammation of a disk in the spine)
• Uveitis (deep eye inflammation)
• Multiple joint arthritis
• Glomerulonephritis (kidney inflammation and protein loss)

Most of the time, the only sign is aborted pregnancy between the 45^th and 59^th day of pregnancy (relatively late in the pregnancy). Classically, the aborted pups appear to have died at least several days prior to abortion as they do not look freshly dead. Abortion does not always appear in this most common form, though. Sometimes, the pregnancy is lost so early in its course that the problem is mistaken for infertility. Sometimes, puppies are stillborn. Sometimes, they are born live and infected.

Testing

Direct culture of the organism from a dead puppy, infected dog’s blood or from secretion is confirmatory but the organism is difficult to isolate in this way. This means we usually depend on immunologic tests. Which test is selected depends on what the test is being used for.

Screening before Breeding

The RSAT (rapid slide agglutination test) is a test that can readily identify negative dogs. That is, if the test comes out negative, the dog can be considered negative. If the test comes out positive, further testing is needed. Up to 60% false positives occur. A test kit is available inside the veterinary hospital and some facilities can perform this test while you wait.

The IFA (Immunofluorescent Antibody) test is a similar screening test, but it must be sent to the reference laboratory. The same guidelines apply negative means negative, and positive means do further tests. That said, if there is a classic history (such as an aborted litter of puppies) along with a positive IFA test, it may not be necessary to do further testing, as the situation is clear.

Further Testing for RSAT or IFA Positive Dogs

There are two tests that fit in this category. The most specific test (meaning the most trustworthy positive value) is the AGID (agar gel immunodiffusion) test. A version of the test called the CPAGID, named for the bacterial protein it detects, is the most accurate of all.

Another test is called a TAT (tube agglutination test). It looks for antibodies against Brucella canis. Antibiotic treatment with tetracyclines can drop antibody levels low enough for the TAT to be negative but this does not necessarily indicate that the infection has cleared. At this time the CPAGID is favored over TAT.

If a dog is to travel to Australia, a TAT test is required as part of the travel documentation. If a dog is to travel to New Zealand, an AGID test is required as part of the travel documentation.

Treatment

First and foremost, the dog in question must be removed from the breeding program by either spay/neuter or euthanasia. The dog can remain as a pet but probably should not be sold due to potential health risks to potential buyers.

 If the dog is to remain as a pet, there are several considerations that must be observed:

1) BRUCELLOSIS IS CONSIDERED TO BE A PERMANENT INFECTION! This means that precautions against human exposure must be maintained for the life of the animal.

2) The dog should be confined to the owner’s property for life. This means that veterinary services should be provided by a house call veterinary service and grooming services should be provided by a mobile service. Obviously, these service providers should be warned about the dog’s condition so that proper protective gear can be employed.

3) The dog can NEVER have contact with pregnant women, children, elderly people, people on chemotherapy or anyone considered to have a compromised immune system. Most human cases are mild and flu-like, but certain “at risk” human populations can have more serious consequences.

4) No exposure to any other dogs. All body secretions of an infected dog and contagious.

5) The infected dog will need to be on antibiotics (see below) as long as tests are positive. Ideally, testing (such as gel immunodiffusion) should be done monthly. Antibiotics can be discontinued as long as tests are negative but they will invariably become positive again eventually necessitating more antibiotics.

ANTIBIOTIC TREATMENTS

Tetracycline and Streptomycin

In this regimen, tetracycline is given twice daily for a month, and injectable streptomycin is given daily for the first and last week of the month. In one study, over half the dogs were considered cured with this regimen, but currently, streptomycin is difficult to come by (as it is considered old-fashioned and has few uses at this time).

Minocycline and Streptomycin

Minocycline and doxycycline are derivatives of tetracycline that can also be used to treat brucellosis, but neither is effective when used alone. Again, four weeks of treatment is needed. Minocycline is used once daily while the aminoglycoside is used daily during the first and last week.

Lack of availability of streptomycin has been a problem in treating this condition. Aminoglycosides such as gentamycin have been proposed as substitutes but they are not as effective. Quinolone antibiotics such as enrofloxacin have also been proposed as substitutes, and are much less toxic than aminoglycosides; they may emerge as the best replacement for streptomycin.

Doxycycline and an Aminoglycoside

This regimen requires daily injections of the aminoglycoside antibiotic for the first and last weeks of a four-week course of treatment. The aminoglycosides are a class of antibiotics that has some very real negative effects on the kidney and so a longer course is not without risk. Monitoring may be needed. Newer literature suggests replacing the aminoglycoside with rifampin.

Because of the potential for human exposure, euthanasia has been encouraged for dogs confirmed to be positive. In some states, euthanasia of positive dogs is mandatory. If you choose to keep a positive dog for a pet, see the links below to minimize contact with infected body fluids.

Keeping Brucella Out of the Kennel

A new dog for a breeding kennel should be isolated for one month. Two Brucella tests two to three months apart should be adequate to confirm negativity (it takes 8-12 weeks from infection for tests to turn positive).

If an infection is detected in a kennel, the entire kennel population should be evaluated and re-screened every 3 months. The kennel should be quarantined until all dogs have tested negative three times with 3 months between tests. Positive dogs should be removed from the kennel.