Ip - Infectious & Parasitic Diseases

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- Infectious & Parasitic Diseases CANINE EHRLICHIOSIS A SILENT KILLER Dr. Gad Baneth, DVM, PhD, Dipl. ECVCP Professor of Veterinary Medicine School of Veterinary Medicine Hebrew University P.O. Box 12 Rehovot 76100 Izrael baneth@agri.

1 - Infectious & Parasitic Diseases CANINE EHRLICHIOSIS A SILENT KILLER Dr. Gad Baneth, DVM, PhD, Dipl. ECVCP Professor of Veterinary Medicine School of Veterinary Medicine Hebrew University P.O. Box 12 Rehovot Izrael baneth@agri.huji.ac.il Introduction Ehrlichial organisms are obligatory intracellular bacteria of the order Rickettsiales. Recently, the nomeclature of organisms in this order was revised. Ehrlichioses are caused by organisms of the genera Ehrlichia, Anaplasma and Neorickettsia. Ehrlichia canis and E. chaffeensis infect monocytes, Anaplasma phagocytophilum and E. ewingii infect granulocytes, and A. platys infects platelets. The significance of the ehrlichioses has been highlighted since the discovery and emergence of the human ehrlichioses caused by E. chaffeensis, E. ewingii, and A. phagocytophilum. Most ehrlichioses are tick borne diseases. Etiology of canine monocytic ehrlichiosis Ehrlichia canis, the etiologic agent of canine monocytic ehrlichiosis, has been recognized worldwide as an important canine infectious agent. Ehrlihcia canis infection has been reported from Africa, Asia, America, and Europe. Autochtonous (non-imported) cases of Ehrlichia canis in Europe have been reported mostly from Spain, Portugal, Southern France, Corsica, Italy including Sardinia, and Greece. Ehrlichia canis morulae found in monocytes and macrophages are a microcolony of bacteria surrounded by a membranous vacuole. Morulae may contain 100 or more ehrlichiae resembling elementary bodies of chlamydiae. E. canis is transmitted by the three-host tick Rhipicephalus sanguineus. The pathogenesis of the disease involves an incubation period of 8-20 days, followed by 3 consecutive phases: an acute phase which lasts 1-4 weeks, a subclinical phase which may last from months to years, and a chronic phase. Not all infected dogs develop the chronic severe form of the disease and the conditions that lead to the development of this stage are unknown. Clinical findings The clinical presentation of the disease caused by E. canis may vary, and the clinical signs most frequently reported are depression, lethargy, anorexia, fever, lymphadenomegaly, splenomegaly and hemorrhages (mainly petechiae, ecchymoses and epistaxis). Ocular manifestations of canine ehrlichisosis include anterior uveitis, keratoconjuctivitis, hyphema, glaucoma, chorioretinitis and retinal detachment. Polyarthritis and polymyositis have been described in E. canis infection. The neurological abnormalities found in canine ehrlichiosis are associated with vasculitis, meningoencephalitis, lymphocytic infiltration of the central and peripheral nervous system or hemorrhages. Renal pathology has been associated with canine ehrlichiosis due to immune-complex glomerulonephritis. Ehrlichia canis infection has been termed by some clinicians as the silent killer. It is often inapparent during the early and sub-clinical stages of infection. When the disease is diagnosed in the chronic stage, it may be too late to save the canine patient as treatment may not be helpful in reversing the severe pancytopenia and immune mediated phenomena associated with this disease. Laboratory findings Laboratory abnormalities in canine monocytic enrlichiosis include hematologic and serum biochemistry changes. Thrombocytopenia is the most frequent hematological abnormality occurring in more than 90% of cases. Anemia, usually non-regenerative normocytic and normochromic, is another common finding in this disease. In addition, mild to severe leucopenia is a frequent abnormality. Hyperglobulinemia, hypoalbuminemia and mild elevation of alkaline phosphatase (ALP) and alanine aminotransferase 479

2 Close window to return to IVIS 480 (ALT) activities are frequently reported in ehrlichiosis. Dogs in the chronic severe stage of the disease may develop severe pancytopenia as their bone marrow becomes hypocellular. The prognosis of these chronically ill dogs is grave. Immune-mediated responses play a major role in the pathogenesis of E. canis infection. Anti-platelets antibodies (APA) have been demonstrated less than a week after experimental E. canis infection of dogs. Platelet aggregation abnormalities, anti-nuclear antibodies (ANA), RBC autoagglutination with positive coombs test, and circulating immune-complexes have been shown in infected dogs and are associated with the disease process. The decrease in platelets during canine ehrlichiosis is probably a result of several mechanisms. These mechanisms include increased consumption with vascular endothelial changes, platelet sequestration and pooling in the spleen, thrombophagocytosis with immunological destruction, a decrease in the half life time of circulating platelets possibly due to opsinization with antibodies, and production impairment due to bone marrow destruction and hypocellularity. In addition to the decrease in circulating platelet number, platelets dysfunction (thrombocytopathy) has also been implicating as an additional factor contributing to lack of platelet functionality in canine monocytic ehrlichiosis. Co-infections with hemoparasites or other infectious agents are often detected in conjunction with canine ehrlichiosis. Hepatozoon canis and Babesia canis vogeli are transmitted by the same vector tick, R. sanguineus. In addition, Leishmania infantum is another common co-infecting protozoal pathogen whose vector, phlebotomine sand flies are often found in the same sub-tropical climate conditions and ecological niches, as R. sanguineus ticks transmitting E. canis infection. Diagnosis The laboratory diagnosis of E. canis infection includes evaluation of the hemogram and serum biochemistry panel. The detection of morulae in monocytes in stained blood smears is rare and can not serve as a main diagnostic option. Anti-E. canis antibodies can be detected in dogs infected with this pathogen and persist long after recovery from the disease. Serum antibodies are thought not to be protective or play an important role in eliminating this intracellular infection. Serology is indicative of exposure to E. canis and may often be helpful in ruling out progressive infection. Antibodies may not be detectable during the early stage of infection. However, seropositive dogs with previous exposure to the pathogen may also present due to other urgent disease conditions. Several commercial in house test kits are available for E. canis infection in addition to the laboratory indirect fluorescent antibody test (IFAT) which is often considered the golden standard for serology. Some serologic cross-reactivity between different Ehrlichia species may occur. Anti-E. canis antibodies have been reported to cross-react with E. chaffeensis, A. phagocytophilum & E. ewingii but not with A. platys. Detection of the presence of E. canis DNA by the polymerase chain reaction (PCR) is highly sensitive and specific and has become a popular assay in research of this disease as well as in its clinical diagnosis. Treatment and prevention Ehrlichial organisms are susceptible to tetracyclines, and doxycycline is most widely used for treatment of infection. Doxycycline is very efficient in clearing rickettsemia in acute cases of E. canis infection. Clinical recovery is noticed within hours, yet treatment should be commenced for 3 weeks, as some dogs may remain carriers when shorter treatments are applied. Treatment with the injectable drug imidocarb dipropionate has been shown to be ineffective in eliminating E. canis in some cases. However, it is often used in combination with doxycyline when Babesia co-infection is suspected. The control of tick infestation by topical treatment with acaricidals and environemental eradication of ticks is recommended for the prevention of E. canis infection. References Baneth, G., Waner, T., Koplah, A., Weinstein, S., Keysary, A Survey of Ehrlichia canis antibodies among dogs in Israel. Vet. Rec. 138: Frank, J.R., Breitschwerdt, E.B A retrospective study of ehrlichiosis in 62 dogs from North Carolina and Virginia. J. Vet. Intern. Med. 13: Dumler, J.S., Barbet, A.F., Bekker, C.P.J., Dasch, G.A., Palmer, G.H., Ray, S.C., Rikihisa, Y., Rurangwira, F.R Reorganization of genera in the families Rickettsiacea and Anaplasmatacea in the order Rickettsiales: unification of some species of Ehrlichia with Anaplasma, Cowdria with Ehrlichia and Ehrlichia with Neorickettsia, description of six new species combinations and designation of Ehrlichia equi and HGE agent as subjective synonyms of Ehrlichia phagocytophilum. Int. J. Syst. Evol. Microbiol. 51: Harrus, S., Kass, P.H., Klement, E., Waner. T Canine monocytic ehrlichiosis: a retropsective

3 study of 100 cases, and an epidemiological investigation of prognostic indicators for the disease. Vet. Rec. 141: Harrus. S., Kenny, M., Miara, L., Aizenberg, I., Waner, T., Shaw, S Comparison of simultaneous splenic sample PCR with blood sample PCR for diagnosis and treatment of experimental Ehrlichia canis infection. Antimicrob. Agents Chemother. 42: Mylonakis, M.E., Koutinas A.F., Breitschwerdt, E.B., Hegarty, B.C., Billinis, C.D., Leontides, L.S., Kontos, V.S Chronic Canine Ehrlichiosis (Ehrlichia canis): A Retrospective Study of 19 Natural Cases. J. Am. Anim. Hosp. Assoc. 40: Infectious & Parasitic Diseases TWO CAUSES OF CANINE AND FELINE DIROFILARIASIS Dr. Gad Baneth, DVM, PhD, Dipl. ECVCP Professor of Veterinary Medicine School of Veterinary Medicine Hebrew University P.O. Box 12 Rehovot Izrael baneth@agri.huji.ac.il Filariasis in dogs and cats can be caused by a number of species that vary from one geographic region to another. At least 8 different filarial spp. have been described to cause persistent microfilaremia in dogs. Some of the filarial species can be highly pathogenic and cause a life-threatening disease, whereas other species are associated with asymptomatic infection. Dirofi laria immitis and Dirofi laria repens are two filarial species infecting dogs and cats that are often found in the same area but cause different clinical syndromes. Dirofilaria repens infection Filariasis caused by Dirofi laria repens is prevalent in several regions in the world including: the Mediterranean basin, southeastern Europe, Africa and southeast Asia. Due to the recent elevation in the number of human infections in Spain and Italy, it is considered an emerging zoonosis in these countries. Dogs, foxes and cats are the reservoir for this infection and people are accidental dead end hosts in which the life cycle is not completed. The mosquito vectors of D. repens vary in different geographic regions and include species belonging to the genera Culex, Anopheles and Aedes. Microfilariae taken up in the blood meal by Ae. aegpyti mosquitoes migrate to the malphigian tubules where they develop to stage 3 (L 3 ) larvae that reach the proboscis. Larvae injected during the mosquito bite into the skin of the dog migrate through the subcutaneous tissues, develop to L 4, L 5 and adult worms and shed microfilariae in the blood. Canine infection is often an incidental hematological finding, or accompanied by mild clinical signs including skin swelling, hyperpigmentation or subcutaneous granulomas containing adult worms. In humans, immature D. repens migrate in connective tissues and elicit an inflammatory response resulting in the formation of nodules around the worms that are frequently confused with tumors and treated by surgical excision. The manifestations of D. repens infection in people are associated with nodules that have been described from the lung, subcutaneous tissues, epididymis, spermatic cord, omentum, conjuctiva, and the breast. Infections have been recorded to persist for 8 years and can be detected in tourists that have visited endemic areas. Heartworm disease In contrast to the relatively non-pathogenic D. repens, D. immtis is a major pathogen in many parts of the world. Dirofilaria immitis causes heartworm disease in domestic and wild canine 481

4 Close window to return to IVIS 482 and feline spp. in warm and temperate regions. It is present in southern Europe, North and South America, Africa, Asia and Australia. The life cycle of D. immitis is basically similar to that of D. repens. The main difference is that the larvae injected into the skin migrate through the muscles to the lung blood vessels reaching the pulmonary arteries where they continue to mature. Adult worms are found primarily in the pulmonary arteries and in severe infections also in the right side of the heart and occasionally in the vena cava. The pre-patent period, e.g. the time from infection to the appearance of microfilaremia, is approximately 6-7 months and the life expectancy of the worm in the dog is approximately 5 years. Chronic heartworm disease results from progressive proliferative endarteritis and thromboembolism of the pulmonary artery caused mostly by adult worms, and not by juvenile migrating worms. The progressive vascular changes lead to pulmonary hypertension, right ventricular hypertrophy or dilation and cor pulmonale. The first clinical signs of disease typically include exercise intolerance and cough. This is followed by signs of chronic right heart failure including ascites, hepatomegaly, syncope and respiratory signs such as dyspnea, tachypnea, cough and hemoptysis. More acute heartworm disease with a heavy worm burden causes vena caval syndrome with erythrocyte membrane disruption and a hemolytic crisis. Humans can become infected with D. immitis but the worm does not complete its life cycle in people. Wolbachia and dirofilariasis Wolbachia are Gram-negative bacterial endosymbionts of arthropods and filarial worms. Wolbachia have been demonstrated to be transovarially transmitted in the human filarial pathogens Onchocerca volvulus and Brugia malayi. Hosts with filarial infection come into contact with Wolbachia following the death of the filarial parasite. Dogs infected with D. immitis have been shown to mount a specific immune response to Wolbachia antigens. Diagnosis of dirofilariasis The diagnosis of dirofilariasis can be achieved by detection of microfilaremia with microscopic examination of blood smears when microfilaremia is high. The Knott s concentration method allows detection of lower numbers of microfilaria. Failure to detect circulating microfilariae does not rule out infection. There are several D. immitis ELISA tests employing monoclonal antibodies for the detection of circulating D. immitis antigen useful also for the detection of occult infection. Serology for infection of cats is usually aimed at the detection of anti-d. immitis antibodies. The filarial species that have been reported to cause persistent microfilaremia in dogs include D. immitis, D. repens, Acantocheilonema reconditum (formerly Dipetalonema), Acantocheilonema dracunculoides, Brugia malayi, Brugia ceylonensis, Brugia phangi and Cercopithifilaria grassi. The geographic distribution of some fliarial spp. is limited and therefore some spp. can be expected to be found only in certain parts of the world. PCR diagnosis of filariasis in canine blood is available in several laboratories. A recent publication has described an assay that can discriminate between 6 species of canine microfilariae by a single PCR. Treatment and prevention Treatment of infected dogs usually includes the adulticide drug melarsomine hydrochloride injected intramuscularly on two consecutive days followed by microfilaricidal treatment with ivermectin or a related drug. There are several prophylactic drug formulations for the prevention of infection. These include preparations of ivermectin, moxidectin, milbemcycin, spot on selamectin and more. References Anyanwu, I.N., Agbede, R.I.S., Ajanusi, O.J., Umoh, J.U., Ibrahim, N.D.G The incrimination of Aedes (stegomyia) aegypti as the vector of Dirofi laria repens in Nigeria. Veterinary Parasitololgy 92: Baneth, G.,Volanski, Z., Anug, Y, Favia, G., Bain, O., Goldstein, G, Harrus, S Dirofi laria repens infection in a dog: diagnosis and treatment with melarsomine and doramectin. Veterinary Parasitology 105: Bredal, W.P., Gjerde, B., Eberhard, M.L., Aleksandersen, M., Wilhelmsen, D.K. and Mansfield, L.S J. Sm. Anim. Prac. 39: Cancrini G, Allende E, Favia G, Baornay F, Anton F, Simon F Canine dirofilariosis in two cities of southeastern Spain. Vet Parasitol 92: Kamalu, B.P., Canine filariasis in southeastern Nigeria. Bull. Anim. Hlt. Prod. Afr. 34: Kamalu, B.P., 1991.Canine filariasis caused by Dirofi laria repens in southeastern Nigeria. Vet. Parasitol. 40: Ferasin L Disease risks for the traveling pet: Heartworm disease. In Practice July/August Gardiner CH, Oberdorfer CE, Reyes JE, Pinkus

5 WH, Infection of man by Dirofilaria repens. Am J Trop Med Hyg 27: Kramer, L., Simon, F., Tamarozzi, F., Genchi, M., Bazzocchi, C Is Wolbachia complicating the pathological effects of Dirofi laria immitis infections? Vet. Parasitol. 133: Orihel, T.C., Helentjaris, D., Alger, J Subcutaneous dirofilariasis: single inoculum, multiple worms. Am J Trop Med Hyg 56: Pampiglione, S., Rivasi, F. and Canestri Trotti, G Human pulmonary dirofilariasis in Italy. Lancet Feb. 11: 333. Pampiglione, S. and Fedeli, F Dirofilariasi polmonare umana: aspetti parassitologici del secondo caso segnalato in Italia. Parassitologia. 33: Pampiglione, S., Rivasi, F., Boldorini, R., Incenasti, R.M., Pastomerlo, M., Pavesi, M., Ramponi, A Dirofilariasis due to Dirofilaria repens in Italy, an emergant zoonosis: report of 60 new cases. Histopathology. 38: Rishniw, M., Barr, S.C., Simpson, K.W., Frongillo, M.F., Franz, M., Dominguez Alpizar J.L Discrimination between six species of canine microfilariae by a single polymerase chain reaction. Vet. Parasitol. 135: Tarello, W La dirofilariose sous-cutanee a Dirofi laria (Nochtiella) repens chez la chien. Revue bibliographique et cas clinique. Revue. Med. Vet. 150: Vakalis, N.C. and Himonas, C.A., Human and canine dirofilariasis in Greece. Parassitologia. 39: Wieslaw, J.K What is new in the Wolbachia/Dirofilaria interaction. Vet. Parasitol. 133:

Suggested vector-borne disease screening guidelines

Suggested vector-borne disease screening guidelines SNAP Dx Test Screen your dog every year with the SNAP Dx Test to detect exposure to pathogens that cause heartworm disease, ehrlichiosis, Lyme disease