Ip - Infectious & Parasitic Diseases

Ip - Infectious & Parasitic Diseases USE OF SEROLOGY FOR THE PREDICTION OF CANINE AND FELI- NE CORE VACCINE NEEDS Michael R. Lappin, DVM, PhD, DACVIM Professor Department of Clinical Sciences Colorado State University Fort Collins Colorado 80523 USA mlappin@colostate.edu 474 Feline vaccine serology Feline vaccines occasionally induce side-effects including an association with formation of soft tissue sarcomas. Adjuvanted rabies virus and feline leukemia virus vaccines cause the most inflammation and have been linked most frequently to tumor production but soft tissue sarcomas have also developed at the site of subcutaneous inoculation with modified live or killed feline herpesvirus 1 (FHV-1), calicivirus (FCV), and panleukopenia virus (FPV) vaccines (FVRCP). Recently, administration of FVRCP vaccines arentally has been linked to the production of antibodies against the cell line used to grow some vaccine viruses. In some cats, those antibodies cross react with renal and other tissues. While a disease association has not been shown, it is another factor to consider when determining an optimal vaccination protocol for an individual cat. The duration of immunity for some feline vaccine antigens is known to be > 3 years. Thus, the American Association of Feline Practitioners/ Academy of Feline Medicine (AAFP/AFM) and others have questioned the need for annual vaccination with FVRCP products after the 1 year booster immunization. It is unknown to what extent humoral or cell-mediated immunity is responsible for the protection elicited by FPV, FHV, or FCV vaccination. The humoral immune response to FCV, FHV-1, and FPV vaccines can be readily measured by the detection of virus-specific antibodies. Quantification of cellmediated immune responses is difficult and is not typically performed on a routine diagnostic basis. In general, presence of serum antibodies indirectly suggests that cell-mediated immune responses are also intact as B lymphocytes (humoral) require T lymphocyte (cell-mediated) help to maintain antibody production. Regardless whether humoral immunity is responsible for protection, if the presence of virus-specific antibody correlated with protection from challenge with FPV, FCV, and FHV-1, serologic screening of individual vaccinated cats could be used to predict vaccine needs. In one study, serum antibodies against FHV-1, FCV, and FPV could be detected in 100% of c ats inoculated twice with a killed FVRCP product 3 years previously. When these cats were challenged with virulent virus 7.5 years after vaccination, the cats were 100% protected against FPV (Scott et al, 1999). When challenged with virulent FHV-1 and FCV, clinical signs of disease in the vaccinated cats were decreased 52% and 63%, respectively, when compared to unvaccinated controls. Virus neutralization (FHV-1, FCV) and hemagglutination inhibition (FPV) assays have classically been used to assess antibody responses to FVRCP vaccines. These assays are labor intensive, are only available in specialized laboratories, and are usually not standardized between laboratories. There are now other techniques on the world market for detection of antibodies. For example, enzyme-linked immunosorbent assays (ELISAs) using whole virus or virus infected cell preparations have been used for detection of antibodies specific for FCV and FHV-1 and are potentially more sensitive than virus neutralization techniques. In addition, ELISAs are technically less complicated, can be standardized for use in multiple laboratories, and can be adapted for use in the veterinary clinic. In one study, serum antibody responses to feline panleukopenia virus (FPV), feline herpesvirus 1 (FHV-1), and feline calicivirus (FCV) were compared to resistance to challenge with the respective virulent viruses in experimental cats. In total, 72 laboratory-reared cats were used and then adopted to private homes. In 4 separate experiments, cats were either vaccinated against FPV, FHV-1, and FCV using an intranasal

Ip vaccine or one of two subcutaneous vaccines or maintained as unvaccinated controls. Between 9 and 36 months after vaccination, the cats were challenged with virulent viruses using USDA protocols for vaccine approval. ELISAs for detection of FPV, FHV-1, and FCV antibodies were developed (HESKA Diagnostic Laboratory, Fort Collins, CO). Serum antibody levels as determined by ELISAs as well as hemagglutination inhibition (HI) for FPV and serum neutralization (SN) for FHV-1 and FCV (New York State Veterinary Diagnostic Laboratory) were correlated to resistance to viral challenge. When used with vaccinated cats, the positive predictive value of FPV, FHV-1, and FCV antibodies as detected by ELISAs were 100%, 90.5%, and 100%, respectively. When used with vaccinated cats, the positive predictive value of FPV, FHV-1, and FCV antibodies as detected by HI or SN were 100%, 91.3%, and 100%, respectively. The ELISAs were also applied to sera from 276 client-owned cats. The seroprevalences for FPV, FHV-1, and FCV were 68.5%, 70.7%, and 92.4%, respectively. It was concluded that when used with vaccinated cats, positive antibody tests for FPV, FHV-1, FCV correlate to resistance to challenge in most cats regardless of vaccine type or interval. Whether use of serum antibodies to predict resistance to infection with FPV, FCV, and FHV-1 would be affected by route of vaccine administration or vaccination interval was previously unknown since only a single long term study using one product was reported. In the study described, two FPV and FHV-1 vaccines and 3 FCV vaccines were assessed. Additionally, interval between vaccination and challenge varied from 9 months to 31 months for FHV-1 and FPV and from 9 months to 36 months for FCV. Positive predictive values of the serum antibody tests were similar regardless of the vaccine or vaccine interval. Since the majority of client-owned cats are seropositive for these agents with antibody titers that predict resistance to infection, use of arbitrary vaccination intervals is likely to lead to unnecessary vaccination of some cats. If validated assays are available, serological testing for prediction of FVRCP antigen needs appears to be appropriate for use in lieu of arbitrary vaccination intervals. It is possible that in the future, serological tests could be used to predict vaccine needs for other antigens, potentially feline leukemia virus and rabies virus. However, at this time, information concerning use of serological tests for other feline vaccine antigens is largely unavailable and is not recommended. Canine vaccine serology Like cats, vaccine associated side-effects in dogs are rare. However, over-vaccination occasionally causes problems and so if a vaccine antigen is not needed, it should not be given. For dogs in the United States, core vaccines include canine distemper virus, parainfluenza, adenovirus 2, parvovirus, and rabies. Puppies are generally vaccinated every 3-4 weeks with distemper, parvovirus, and adenovirus 2 vaccines until 14-16 weeks of age. At one year of age or one year later the dog should return for a booster vaccination. After one year of age, risk of infection by canine distemper virus, parainfluenza, adenovirus 2, and parvovirus should be assessed yearly while performing a physical examination and checking for enteric parasites. In several studies, canine distemper virus titers and canine parvovirus titers suggestive of resistance were detected in >95% of the dogs tested, respectively. Canine parvovirus vaccines may provide life-long immunity and distemper virus titers are detected for up to 10 years in many dogs. Thus, in low risk dogs, modified live DA2PP vaccines should be administered no more often than every third year. In addition to serological studies, challenge studies from several vaccine manufacturers have shown at least 36-57 week duration of immunity to infectious canine adenovirus, distemper, and parvovirus on challenge. Positive serologic tests for canine distemper virus, canine adenovirus 1, and canine parvovirus are predictive of resistance. If validated assays are available, serological testing for prediction of these vaccine antigen needs appears to be appropriate for use in lieu of arbitrary vaccination intervals. For some vaccine antigens, serology is not predictive. For example, some dogs with serological responses to Borrelia burgdorferi and leptospires can still be infected with the organism. For other vaccine antigens, information or validated assays are not currently available. SUGGESTED READINGS 1. Lappin MR, et al. Prediction of resistance to feline parvovirus, feline herpesvirus 1 and feline calicivirus challenge utilizing serology. J Am Vet Med Assoc 2002; 220: 38-42. 2. Lappin MR, et al. Investigation of the induction of antibodies against Crandell-Rees feline kidney cell lysates and feline renal cell lysates after parenteral administration of vaccines against feline viral rhinotracheitis, calicivirus, and panleukopenia in cats. Am J Vet Res 2005; 66: 506-511. 475

3. Mouzin DE, et al. Duration of serologic response to three viral antigens in cats. J Am Vet Med Assoc 2004; 224: 61-66. 4. Mouzin DE, et al. Duration of serologic response to five viral antigens in dogs. J Am Vet Med Assoc 2004; 224: 55-60. 5. Paul MA, et al. 2006 AAHA Canine Vaccine Guidelines. J Am Anim Hosp Assoc 2006; 42: 80-89. 6. Richards J, et al. Feline vaccine selection and administration. Compend Cont Ed Pract Vet 2001; 23: 71-80. 7. Schultz RD. Duration of immunity for canine and feline vaccines: A review. Vet Microbiol 2006 April 18, Epub ahead of print. 8. Scott FW, Geissinger C. Duration of immunity in cats vaccinated with an inactivated feline panleukopenia, herpesvirus, and calicivirus vaccine. Fel Pract 1997; 25: 12-19. 9. Scott FW, Geissinger CM. Long term immunity in cats vaccinated with an inactivated trivalent vaccine. Am J Vet Res 1999; 60: 652-658. 10. Scott-Moncrieff JC, et al. Evaluation of antithyroglobulin antibodies after routine vaccination in pet and research dogs. J Am Vet Med Assoc 2002; 221: 515-521. 11. Tizard I, Ni Y. Use of serologic testing to assess immune status of companion animals. J Am Vet Med Assoc 1998; 213: 54-60. 12. Twark L, Dodds WJ. Clinical use of serum parvovirus and distemper virus antibody titers for determining revaccination strategies in healthy dogs. J Am Vet Med Assoc 2000; 217: 1021-1024. Ip - Infectious & Parasitic Diseases UPDATE ON THE FLEA-ASSOCIATED AGENTS OF CATS; BARTONELLA SPP., HEMOPLASMA SPP., AND RICKETTSIA FELIS Michael R. Lappin, DVM, PhD, DACVIM Professor Department of Clinical Sciences Colorado State University Fort Collins Colorado 80523 USA mlappin@colostate.edu 476 Bartonella spp. Bartonella henselae is a gram negative organism that replicates within erythrocytes and endothelial cells. The organism is the most common cause of cat scratch disease as well as bacillary angiomatosis, and bacillary peliosis, common disorders in humans with AIDS. Humans with cat scratch disease develop a variety of clinical signs such as lymphadenopathy, fever, malaise, weight loss, myalgia, headache, conjunctivitis, skin eruptions, and arthralgia. Most cases of cat scratch disease are self-limiting but may take several months to completely resolve. Cats can also be infected with B. clarridgeiae, an organism that has also been associated with cat scratch disease. It is currently unknown whether other Bartonella spp. that infect cats are common or associated with human or feline disease. Bartonella henselae is transmitted between cats by fleas. Based on seroprevalence studies in cats, exposure to Bartonella spp. varies by region around the world but exposure is very common. The prevalence rates for B. henselae in blood of cats and fleas collected off their bodies were 34.8% and 22.8%, respectively. The prevalence rates for B. clarridgeiae in cats and their fleas were 20.7% and 19.6%, respectively. Bartonella henselae survives in flea feces for days after passed by infected C. felis. Thus, cat claws and teeth may be contaminated with the organism by

Ip ingesting fleas or flea feces during grooming and then transmit the organisms to people by bites. Most seropositive, blood culture positive, or PCR positive cats are clinically normal. However, Bartonella spp. infection of cats has also been associated directly or indirectly with a variety of clinical manifestations like fever, lethargy, lymphadenopathy, uveitis, gingivitis, and neurological diseases. How often cats become ill from Bartonella spp. infections is unknown and more information is needed. However, it can be difficult to determine which cats have been exposed and which cats are diseased. For example, in recent studies of stomatitis, seizures, and uveitis in cats, the prevalence rates for Bartonella spp. antibodies in feline sera were not significantly different for cats with and without disease. It is also still also still unclear as to why some cats develop Bartonella associated illness and others do not. Immune suppression or pathogenic strains are possible explanations. Blood culture, PCR assay on blood, and serologic testing can be used to assess individual cats for Bartonella infection. However, there is no positive result that correlates to clinical illness. Cats that are culture-negative or PCRnegative and antibody-negative and cats that are culture-negative or PCR-negative and antibodypositive are probably not a source of flea, cat, or human infection. However, bacteremia can be intermittent and false-negative culture or PCR results can occur, limiting the predictive value of a single battery of tests. With PCR, false positive results can occur and positive results do not necessarily indicate that the organism is alive. While serologic testing can be used to determine whether an individual cat has been exposed, both seropositive and seronegative cats can be bacteremic, limiting the diagnostic utility of serologic testing. Thus, testing healthy cats for Bartonella spp. infection is not currently recommended in most situations. Testing should be reserved for cats with suspected clinical bartonellosis. If the results of Bartonella tests are negative in a clinically ill cat, the organism is not likely the cause of the clinical syndrome unless the infection was peracute and serological testing was used as the diagnostic test. If the results of Bartonella tests are positive, the agent remains on the differential list, but other causes of the clinical syndrome must also be excluded. If no other cause of the clinical syndrome can be determined, a therapeutic trial with a drug with presumed anti-bartonella activity could be started. Administration of doxycycline, amoxicillin-clavulanate, erythromycin, or fluoroquinolones can limit bacteremia but does not cure infection in all cats and has not been shown to lessen the risk of cat scratch disease. Thus, treatment is generally recommended for clinically ill cats. Doxycycline at 10 mg/kg, PO, daily, formulated into a flavored suspension (to avoid esophageal strictures) for 7 days is the first drug of choice. If a positive response is achieved, continue treatment for 2 weeks past clinical resolution of disease or for a minimum of 28 days. If a poor response is noted and bartonellosis is a differential diagnosis, azithromycin or a fluoroquinolones are considered appropriate choices. Difficulty in treatment may relate to the intracellular location of the organism. Cats with uveitis thought to be from bartonellosis should be topically with glucocorticoids to attempt to lessen inflammation and subsequent glaucoma. To lessen the likelihood of acquiring a Bartonella spp. infection from a cat, the following were adapted from what is recommended to HIVinfected people and other cat owners by the Centers for Disease Control and the American Association of Feline Practitioners: 1. Flea control should be maintained; 2. If a family member is immunosuppressed and a new cat is to be acquired, adopt a healthy cat > 1 year; 3. Declawing is generally not advised, but immunosuppressed people should avoid bites and scratches; 4. Cat-associated wounds should be washed promptly and medical advice sought; and 5. Cats should not be allowed to lick open wounds on immunosuppressed people. Hemoplasma spp. There are three epi-erythrocytic hemoplasmas of cats that are currently recognized; Mycoplasma haemofelis (Mhf), Candidatus M. haemominutum (Mhm), and Candidatus M. turicensis. These organisms were previously called Haemobartonella felis. The organisms are likely worldwide. Mycoplasma haemofelis appears to be the most pathogenic species. In prevalence studies performed with assays capable of amplifying both Mhf and Mhm, both organisms have been detected and Mhm infection is most common. In a recent study, we collected fleas from cats and attempted to amplify hemoplasma DNA from flea digests as well as the blood of the cat. The prevalence rates for Mhf in cats and their fleas were 7.6% and 2.2%, respectively. The prevalence rates for Mhm in cats and their fleas were 20.7% and 23.9%, respectively. In addition, fleas ingest Mhm and Mhf from infected cats when feeding. Hemoplasmas have been transmitted experimentally by IV, IP, and oral inoculation of blood. Transmission by biting has been hypothesized. Red blood cell destruction is 477

due primarily to immune-mediated events; direct injury to red blood cells induced by the organism is thought to be minimal. Clinical signs of disease depend on the degree of anemia, the stage of infection, and the immune status of infected cats. Pale mucous membranes, depression, inappetence, weakness, and occasionally, icterus and splenomegaly are most common. Fever occurs in some acutely infected cats and may be intermittent in chronically infected cats. Evidence of coexisting disease may be present. Weight loss is common in chronically infected cats. Cats in the chronic phase can be subclinically infected only to have recurrence of clinical disease following periods of stress. Fever has been associated with chronic infections. Diagnosis is based on demonstration of the organism on the surface of erythrocytes on examination of a thin blood film or amplification of microbial DNA by PCR assay. Organism numbers fluctuate and so blood film examination can be falsely negative up to 50% of the time. The organism may be difficult to find cytologically, particularly in the chronic phase. Real time PCR to quantify hemoplasma DNA has now been titrated and can be used to monitor response to treatment. Doxycycline has less side effects than other tetracyclines in cats and so is preferred. Doxycycline is administered as a flavored suspension (to avoid esophageal strictures) at 10 mg/kg, PO, every 24 hours for 7 days. If there is a positive response and the cat is tolerating the drug, treatment is continued for a total of 28 days if possible. If autoagglutination is evident, prednisolone at 1 mg/kg, PO, every 12 hours is given for the first 7 days or until autoagglutination is no longer evident. In cats intolerant of doxycycline, enrofloxacin (5 mg/kg, PO, daily), marbofloxacin (1.25 mg/lb, PO, daily), or imidocarb (5 mg/kg, SQ or IM, every 14 days) may be effective. Azithromycin was not effective for the treatment of hemoplasmosis in one study. Blood transfusion should be given if clinically indicated. Treatment does not always eliminate infection and re-infection can occur. To attempt to prevent feline hemoplasma infections, flea control should be maintained. Cats should be housed indoors to avoid vectors and fighting. Clinic blood donor cats should be screened for both Mycoplasma spp. by PCR prior to use. There are currently no known human health risks. Rickettsia felis Rickettsia felis is a spotted fever group organism occasionally associated with fever, headache, myalgia, and macular rash in people. It has been detected in Ctenocephalides felis, C. canis, and Pulex irritans; these fleas have a worldwide distribution. Rickettsia felis has been determined in C. felis collected from cats in several countries around the world. In a study recently completed in my laboratory, 67.4% of fleas collected from 92 cats were PCR positive for R. felis DNA. Rickettsia spp. antibodies are commonly detected in cats in the United States; it is likely the cats are exposed to R. felis because C. felis is common. However, we failed to detect R. felis DNA in cats with fever in the United States. Thus, further data is needed to determine whether the organism induces illness in cats. Summary Because Bartonella spp., Hemoplasma spp., and R. felis infections of fleas are so common and because significant illness can occur in cats (Bartonella spp. and hemoplasmas) and people (Bartonella and R. felis), flea control is now recommended for all cats in the United States. ADDITIONAL REFERENCES AVAILABLE UPON REQUEST 1. Boulouis HJ, et al. Factors associated with the rapid emergence of zoonotic Bartonella infections. Vet Res 2005; 36: 383-410. 2. Comer JA, et al. Urban zoonoses caused by Bartonella, Coxiella, Ehrlichia, and Rickettsia species. Vector Borne Zoo Dis 2001; 1: 91-118. 3. Tasker S, Lappin MR. Haemobartonella felis: recent developments in diagnosis and treatment. J Fel Med Surg 2002; 4: 3-11. Webpages: aafponline.org; capcvet.org; cdc.gov 478