Lyme borreliosis remains a laboratory diagnosis

Article

Unfortunately, Lyme borreliosis disease in animals has become more of a laboratory diagnosis rather than a clinical diagnosis.

Author's note: Last month began a two-part series on Lyme diseasein dogs. Beginning on page 6S of the April issue, the series addressed cause,transmission, pathogenesis and clinical disease. This month, the discussioncontinues on diagnosis, treatment and prevention.

Diagnosis

Unfortunately, Lyme borreliosis disease in animals has become more ofa laboratory diagnosis rather than a clinical diagnosis.

There are no specific hematologic or serum chemistry profile changespathognomonic of Lyme borreliosis, although CSF, joint fluid and urine mayshow inflammatory changes. The synovial fluid changes in infected dogs havebeen best substantiated with increased cell counts of 5,000 to 100,000 cells/mland neutrophils predominating (>95 percent).

Tickborne transmission results in differences in the outer surface proteinsexpressed on the Borrelia burgdorferi organisms and differences in the host'sserological responses as compared to experimental infections with injectedcultured Borrelia burgdorferi.

The current serologic screening procedure available for animals are basedon ELISA and some indirect FA assays. Most ELISA and indirect FA assaysuse whole cells with many cross-reactive proteins present in other bacteria,especially other Borrelia species and Leptospira species. The presence ofincreased serum antibody titer to Borrelia burgdorferi signifies exposureto the organism but does not prove that the organism causes clinical illness.

In endemic areas, asymptomatic animals are often seropositive. In additionto seropositive results with a validated ELISA or indirect FA assay, theanimal should have a history of tick exposure with compatible clinical signsand a rapid response to antibiotic therapy.

The dependency on serologic testing results from the fact that cultureand microscopic detection of the Borrelia from specimens of tissues or bodyfluids are uncommon. Rather than being a test for Lyme borreliosis disease,serology should be viewed more appropriately as seroreactivity to Borreliaburgdorferi.

The time course of serologic testing is also important in determiningwhether active or past infection is responsible for seropositivity. Earlyserodiagnostic results are usually negative because the immune responseto Borrelia burgdorferi developed gradually. Titer increases almost alwaysprecede clinical lameness and fever in infected dogs. High or persistentserologic titers could indicate past exposure or infection and, as such,are difficult to interpret as single samples and absolute values of titerscan vary widely.

In general, data from most ELISA and indirect FA assays suggests thattiters >1:64 to 1:128 indicate the least significant level of seroreactivity.Titers can be much higher in recently exposed, actually infected animals.High serum antibody titers seem to decline or disappear with antibiotictherapy, but increases in titers that occur after six months following terminationof antibiotic therapy are associated with proliferation of surviving bacteria.Vaccinated dogs show seroreactivity for months to years after vaccination,making a diagnosis difficult with whole cell antigen products. Althoughneutralizing serum antibody titers after vaccination may decrease with time,most ELISA and indirect FA titers remain increased for extended periods,interfering with the standard serologic testing procedures.

Ongoing infections are characterized by high whole Borrelia cell antibodytiters. The use of separated or purified protein antigens in ELISA assayor confirmation with western immunoblotting test should improve specificityof Borrelia burgdorferi antibody assays without loss of sensitivity.

The pattern of serum antibody reactivity after field tick infestationalso differs from that produced after vaccination. Western immunoblottingtest helps determine that clinical significance of whole cell serum antibodytiters when reactivity to other bacteria such as Leptospira species occurs.

New information

A number of novel surface protein antigens may also serve as serologicmarkers of field-exposed infections because in vitro derived Borrelia organismsdo not express these surface protein antigens. There is a unique proteincalled VlsE from Borrelia burgdorferi incorporated in the newly developedcanine Snap, 3Dx test (IDEXX Laboratories). This serologic test detectsthe presence of antibody to a unique outer surface protein of Borrelia burgdorferiin field-infected dogs.

Both Borrelia burgdorferi bacterins and recombinant OspA vaccines areavailable for dogs and offer protection against infection. In the past,a positive serologic test result, denoted exposure to Borrelia burgdorferiwhether or not the dog had previously been vaccinated with any of thesecommercially licensed Lyme borreliosis vaccines available in the USA. Itis also important to note that this new canine Snap, 3Dx test does not detectserum antibody that develops following vaccination.

However, among dogs with clinical signs potentially associated with Lymeborreliosis, a positive canine Snap, 3Dx test may be interpreted as activeinfection. In the absence of clinical signs, a positive canine Snap, 3Dxtest result indicates prior exposure to Borrelia burgdorferi or a dog thathas a subclinical infection. In studies completed with several hundred samplesfrom various parts of the country, the test does not detect serum antibodiesinduced by other pathogenic or nonpathogenic Borrelia species. With caninesera to date, an excellent correlation has been observed between positivecanine Snap, 3Dx test results and western immunoblotting procedures. Thecanine Snap, 3Dx test may serve as a valuable seroprevalence and diagnostictool in determining levels of true infection of Lyme borreliosis in healthydogs and may be incorporated into the practice in a routine annual healthexamination.

Treatment

Several effective antibiotics are available for the treatment of dogswith clinical signs of Lyme borreliosis: doxycycline, amoxicillin, chloramphenicol,azithromycin and ceftriaxone. The antibiotics most commonly used are doxycycline(10 mg/kg q12h PO for a minimum of 30 days) or amoxicillin (20 mg/kg q8hPO for a minimum of 30 days). Chloramphenicol is especially good for dogswith neurologic manifestations and is administered at 15-25 mg/kg orallyq8h for 14-30 days. Antibiotics, such as doxycycline, azithromycin (5 mg/kgq12h for a minimum of 20 days) and ceftriaxone (20 mg/kg q12h for a minimumof 14-30 days), are effective in diminishing organism load in a Borrelia-infecteddog, but they do not eradicate the Borrelia.

Young and growing animals should not be treated with doxycycline - becauseof yellowing of the developing teeth. Improvement should be seen withinthree days of antibiotic treatment. If improvement is not seen, anotherdiagnosis should be considered.

Prevention

Lyme borreliosis disease can be prevented by avoiding tick infestationand/or by annual vaccination. Tick engorgement on dogs may be preventedby tick repellents containing DEET or permethrin, amitraz tick collars and/orby grooming dogs daily. Controlling the tick population in the environmentwould be limited to small areas. Attempts to reduce the deer and/or rodentpopulation has had limited success.

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