Surveillance Vol.17 No.4 1990 Canine heartworm disease Canine heartworm (Dirofilaria immitis) infestation has been detected in New Zealand only in dogs recently introduced to this countryfrom parts of the world where the infestation is endemic. It has not been detected in dogs resident in this county.' Two factors, however, make establishment of Dirofilaria infestation in New Zealand dogs a distinct possibility. The two factors which could make possible the establishment of D. immitis in New Zealand are: 1 The marked increase in prevalence in North America and Australia and its spread to more temperate regions within these continents over the last several years. 2 The presence of suitable mosquito vectors (Aedes notoscriptus and Culex quinquefasciatus) in parts of New Zealand.' Consequently, technical staff of the MAF Animal Health Laboratories routinely screen all canine blood films for microfilariae and attempt to positively identify any present. In reality, this involves differentiating microfilariae of Dipetalonema reconditum from those of Dirofilaria, as Dipetalonema infestation is endemic in New Zealand dogs. Recently Ruakura Animal Health Laboratory received a blood and urine sample for routine clinical pathology examination from a dog suspected of being in renal failure. The results of severe azotaemia, isosthenuria and a non-responsive anaemia confirmed this diagnosis. Occasionalmicrofilariaewere also noted in the blood film but positive identification was not possible because of the low numbers present. A formalinised EDTA blood sample was requested and a Knott's test performed. On morphological grounds this sample appeared to contain both Dirofilaria and Dipetalonema microfilariae. This caused some concern as the subject was a working sheep dog from Gisborne,born in the district. It was therefore considered necessary to investigate the case further. However, in the meantime the dog had been euthanatised because of its deteriorating clinical condition. A postmortem performed at the laboratory revealed a chronic interstitial nephritis, a suppurative prostatitis and left-sided heart failure from a chronic vegetative lesion on the left atrioventricular valve. No adult Dirofilaria were seen, nor were there any pulmonary vascular myointimal proliferations characteristicof heartworm infestation? Serum tested for canine heartworm antigen was negative. Blood samples were collected from five other dogs on the suspect farm. Two had microfilariaein their peripheral blood and those were positively identified as Dipetalonema from length and width measurements (Table 1). All five were seronegative to canine heartworm antigen. In summary, the initial tentative diagnosis of Dirofilaria immitis infestation in a sheep dog from Gisborne was ruled out because: 1 There were no adult worms present (no adulticide treatment had been given). 2 There was none of the vascular pathology commonly seen in heartworm disease. 3 Serology of the initial case and five incontacts was negative. 4 Microfilariae seen in two of five incontacts were confidently identified as Dipetalonema reconditum. References 1 2 3 Belford, C J, McSporran, K D, 1987: Canine heartworndisease. Surveillance 14(4):14-15. Robinson, W F, Maxie, M G, 1985: The Cardiovascular System. In Pathology of Domestic Animals, Third Ed, Jubb, K, Kennedy, P C, Palmer, N. Academic Press, Inc: 46-48. Redinton, B C, Jackson, R F, Goodwin Seymour, W, Otto, G F 1977: The various microfilariae found in dogs in the United States. In Proceedings of the Heartworm Symposium, 1977, Otto, G F (ed.) Bonner Springs, Veterinary Medicine Publishing CO: 14-21. R S Ellison K G Townsend Ruakura Animal Health Laboratory A M McKellow Palmerston Road Veterinary Clinic Gisborne F J A Neilson MAF Quality Management Gisborne I Table 1: Measurementsof microfilariaerecovered from two in-contact dogs 1 AnimalID li Length (10 Width (p) Mean Range Mean 250 247 248 -252 243 -252 4.95 4.95 308 263 295 - 325 250 - 288 Range Reference Measurements' D.immitis D. reconditum 5.0 - 1.5 4.5 - 5.5 Surveillance 17(4) 9