Abstract

Morbilliviruses have emerged as the most potent viral pathogen of pinnipeds and cetaceans.¹ Since 1987, at least eight mass mortality events affecting free-living pinniped and cetacean populations world-wide have been attributed to morbillivirus infection.^2-4 Cetacean morbillivirus (CMV) infection has a worldwide distribution,^5,6 and whist there is serological evidence of morbillivirus infection of several cetacean species within Australian and New Zealand waters,^3,6 to the authors' knowledge, cetacean mortality attributed to CMV infection had not previously been reported in the southern hemisphere. The current report describes a cetacean mortality due to CMV infection in the southern hemisphere. A juvenile, 38.5 kg male offshore bottlenose dolphin (Tursiops truncatus) was found stranded on the eastern (ocean) side of Frazer Island, Queensland, Australia (25°15'S, 153°10'E). The approximately 5 month old dolphin was in fair body condition, unresponsive to external stimuli and unable to swim or float unassisted. At presentation, venous blood was collected for hematologic, biochemical, and serologic analysis. The dolphin died following two days hospitalization, and at necropsy there was extensive pulmonary consolidation. Multiple fresh and formalin-fixed tissues were subjected for laboratory analysis. Results revealed an inflammatory leukogram, with severe lymphopenia but no significant serum biochemistry abnormalities. Leptospirosis microscopic agglutination test, toxoplasmosis direct agglutination test (DAT) and toxoplasmosis modified agglutination test (MAT) were all negative. Morbillivirus serum neutralisation test (SNT) serology was positive at a titer of 1:16 and negative against both Canine distemper virus (CDV) and Phocine distemper virus (PDV). Significant bacterial or fungal growth was not detected. Microscopic findings were similar to those previously described in cetaceans as a result of morbillivirus infection,^2-4,7-9 with death due to a combination of severe pneumonia and encephalitis. 'Warthin-Finkeldey' type syncytia and round to ovoid acidophilic intranuclear inclusion bodies approximately 5 µm–20 µm were present in lung, brain, lymph node and thymic tissues. Ultrastructurally, pulmonary syncytial cells had characteristic intranuclear Paramyxoviridae viral particles. Immunohistochemical detection of morbillivirus antigen in lung, thymus and brain was strongly positive. Morbillivirus infection should be included in the differential diagnosis of stranded or dead dolphins or whales in Australia, particularly if stranded animals display neurological signs. There currently is very limited information regarding the status of CMV infection in the southwest Pacific, and additional studies are needed to further investigate the epidemiology, geographical distribution and seroprevalence of CMV infection in the region. Such studies would allow for the identification of particular cetacean species and/or specific populations with endemic subclinical CMV infection that could potentially act as reservoirs of infection and would also identify those naïve (seronegative) species/populations that are prone to a significant mortality event as a result of CMV introduction.

Acknowledgements

The authors would like to thank the staff at WHO/FAO/OIE Collaborating Centre for Reference and Research on Leptospirosis, Queensland Health Forensic and Scientific Services, Queensland Australia and Animal Health Laboratory, DPIW Tasmania, Australia for performing leptospirosis and toxoplasmosis serology, respectively.

References

1.  Duignan PJ, House C, Geraci JR, Duffy ND, Rima BK, Walsh MT, Early M, St Aubin DJ, Sadove S, Koopman H, Rhinehart H. Morbillivirus infection in cetaceans of the western Atlantic. Vet Microbiol 1995; 44: 241–249.

2.  Di Guardo G, Marruchella G, Agrimi U, Kennedy S. Morbillivirus infections in aquatic mammals: a brief overview. J Vet Med A 2005; 52: 88–93.

3.  Duignan PJ. Diseases of cetaceans and pinnipeds. In: Martin A, Vogelnest editors. Veterinary Conservation Biology: Wildlife Health and Management in Australia. Marine Mammal Strandings. Taronga Zoo. Sydney, NSW. 2001; p.1–25.

4.  Kennedy S. Morbillivirus infections in aquatic mammals. J Comp Pathol 1998; 119: 201–225.

5.  Van Bressem MF, Van Waerebeek K, Fleming M, Barrett T. Serological evidence of morbillivirus infection in small cetaceans from the Southeast Pacific. Vet Microbiol 1998; 59: 89–98.

6.  Van Bressem MF, Van Waerebeek K, Jepson PD, Raga JA, Duignan PJ, Nielsen O, Di Beneditto AP, Siciliano S, Ramos R, Kant W, Peddemors V, Kinoshita R, Ross PS, López-Fernandez A, Evans K, Crespo E, Barrett T. An insight into the epidemiology of dolphin morbillivirus worldwide. Vet Microbiol 2001; 81: 287–304.

7.  Domingo M, Visa J, Pumarola M, Marco J, Ferrer L, Rabanal R, Kennedy S. Pathologic and immunocytochemical studies of morbillivirus infection in striped dolphins (Stenella Coeruleoalba). Vet Pathol 1992; 29: 1–10.

8.  Duignan PJ, Geraci JR, Raga JA, Calzada N. Pathology of morbillivirus infection in striped dolphins (Stenella coeruleoalba) from Valencia and Murcia, Spain. Can J Vet Res 1992; 56: 242–248.

9.  Lipscomb TP, Schulman FY, Moffett D, Kennedy S. Morbilliviral disease in Atlantic bottlenose dolphins (Tursiops truncatus) from the 1987–1988 epizootic. J Wild Dis 1994; 30: 567–571.