Clinical and Pathological Findings of a Newly Recognized Disease of Elephants Caused by Endotheliotropic Herpesviruses

Abstract

The unique clinical and pathological findings in nine Asian (Elephas maximus) and two African (Loxodonta africana) elephants from North American Zoos with a highly fatal disease caused by novel endotheliotropic herpesviruses are described. Identification of the viruses by molecular techniques and some epidemiological aspects of the disease were previously reported. Consensus primer polymerase chain reaction (PCR) combined with sequencing yielded molecular evidence that confirmed the presence of two novel but related herpesviruses associated with the disease, one in Asian elephants and the second in African elephants. Disease onset was acute, with lethargy, edema of the head and thoracic limbs, oral ulceration and cyanosis of the tongue followed by death of most animals in 1 to 7 days. Pertinent laboratory findings in two of three clinically evaluated animals included lymphocytopenia and thrombocytopenia. Two affected young Asian elephants recovered after a 3 to 4 wk course of therapy with the anti-herpesvirus drug famciclovir. Necropsy findings in the fatal cases included pericardial effusion and extensive petechial hemorrhages in the heart and throughout the peritoneal cavity, hepatomegaly, cyanosis of the tongue, intestinal hemorrhage, and ulceration. Histologically, there were extensive microhemorrhages and edema throughout the myocardium and mild, subacute myocarditis. Similar hemorrhagic lesions with inflammation were evident in the tongue, liver, and large intestine. Lesions in these target organs were accompanied by amphophilic to basophilic intranuclear viral inclusion bodies in capillary endothelial cells. Transmission electron microscopy of the endothelial inclusion bodies revealed 80 to 92 nm diameter viral capsids consistent with herpesvirus morphology. The short course of the herpesvirus infections, with sudden deaths in all but the two surviving elephants, was ascribed to acute cardiac failure attributed to herpesvirus-induced capillary injury with extensive myocardial hemorrhage and edema.

Comparative Genome Analysis of Four Elephant Endotheliotropic Herpesviruses, EEHV3, EEHV4, EEHV5, and EEHV6, from Cases of Hemorrhagic Disease or Viremia

“…Because EEHV1A and EEHV1B have been by far the most predominant causative agents of fatal disease in Asian elephants, the focus for this scenario has obviously fallen onto those two virus types in particular. Provocative early PCR evidence suggested that EEHV1A may be present in skin lesions in healthy wild African adult elephants (1,32). However, we have not been able to confirm that result from further evaluation of archival African skin nodule specimens, and no other examples of EEHV1 in African elephants have been found.…”

Endometritis in Postparturient Cattle Associated with Bovine Herpesvirus-4 Infection: 15 Cases

“…However, other distinct endotheliotropic herpesviruses with nucleocapsids of 80-90-nm diameter have recently been described in elephants. 24 Detailed ultrastructural examination of virus in our cases demonstrated enveloped as well as naked cytoplasmic virions and morphologic features characteristic of BHV-4 rather than BAdV. Definitive diagnosis of BHV-4 was possible after PCR results demonstrated characteristic 130-bp bands using BHV-4-specific primers and no bands visible on electrophoretic gels using adenovirus-specific primers.…”

Elephant Endotheliotropic Herpesviruses EEHV1A, EEHV1B, and EEHV2 from Cases of Hemorrhagic Disease Are Highly Diverged from Other Mammalian Herpesviruses and May Form a New Subfamily

“…Most were in captive-born Asian calves between 1 and 8 years old, with a major peak between 1 and 4 years of age. Pathological samples, including both peripheral whole blood and all necropsy tissues tested by PCR carry high levels of EEHV DNA (4,10,13,14).…”

“…The heart, lung, tongue, and most other major internal organs contain typical intranuclear herpesviruslike inclusion bodies and virions in vascular endothelial cells, which contribute to microvascular damage and focal hemorrhagic lesions (13,14). EEHV infections were also responsible for the deaths of the first Asian elephant calves born at the Bronx Zoo (Bronx, New York, NY) and at the Woodland Park Zoo (Seattle, WA), and the first conceived by artificial insemination in both Europe and North America, as well as the first African elephant calf born at the Oakland Zoo (Oakland, CA).…”