Elephant endotheliotropic herpesvirus 5, a newly recognized elephant herpesvirus associated with clinical and subclinical infections in captive Asian elephants (Elephas maximus)

Abstract

Elephant endotheliotropic herpesviruses (EEHVs) can cause acute hemorrhagic disease with high mortality rates in Asian elephants (Elephas maximus). Recently, a new EEHV type known as EEHV5 has been described, but its prevalence and clinical significance remain unknown. In this report, an outbreak of EEHV5 infection in a herd of captive Asian elephants in a zoo was characterized. In February 2011, a 42-yr-old wild-born female Asian elephant presented with bilaterally swollen temporal glands, oral mucosal hyperemia, vesicles on the tongue, and generalized lethargy. The elephant had a leukopenia and thrombocytopenia. She was treated with flunixin meglumine, famciclovir, and fluids. Clinical signs of illness resolved gradually over 2 wk, and the white blood cell count and platelets rebounded to higher-than-normal values. EEHV5 viremia was detectable starting 1 wk before presentation and peaked at the onset of clinical illness. EEHV5 shedding in trunk secretions peaked after viremia resolved and continued for more than 2 mo. EEHV5 trunk shedding from a female herd mate without any detectable viremia was detected prior to onset of clinical disease in the 42-yr-old elephant, indicating reactivation rather than primary infection in this elephant. Subsequent EEHV5 viremia and trunk shedding was documented in the other five elephants in the herd, who remained asymptomatic, except for 1 day of temporal gland swelling in an otherwise-healthy 1-yr-old calf. Unexpectedly, the two elephants most recently introduced into the herd 40 mo previously shed a distinctive EEHV5 strain from that seen in the other five elephants. This is the first report to document the kinetics of EEHV5 infection in captive Asian elephants and to provide evidence that this virus can cause illness in some animals.

Figure 1

Oral hyperemia and tongue vesicles during peak period of clinical illness with apparent association with elephant endotheliotropic herpesvirus 5 (EEHV5) infection. Arrows indicate tongue vesicles in elephant 1 on 7 February 2011.

Figure 2

Kinetics of elephant endotheliotropic herpesvirus 5 (EEHV5) viral loads detected in whole blood (WB) and trunk wash (TW) preparations from seven elephants. VGC: viral genome equivalents. DNA prepared from WB and TW from seven elephants was screened for the presence of EEHV5 nucleic acid using a real-time quantitative polymerase chain reaction (qPCR) assay. Data for TW is expressed as VGC per test reaction and for WB as VGC per milliliter of blood. The y-axis on the graphs shows the quantity of EEHV5 genome copies, and the x-axis shows the number of days over which the study was conducted. Day 0 represents the first day that samples were collected (3 January 2011). Graphs for each animal’s WB and TW EEHV5 profiles are indicated. The time frame during which clinical signs were observed for elephant 1 is designated by the gray bar, and the duration of famciclovir treatment is indicated by a black bar.

Figure 2

Kinetics of elephant endotheliotropic herpesvirus 5 (EEHV5) viral loads detected in whole blood (WB) and trunk wash (TW) preparations from seven elephants. VGC: viral genome equivalents. DNA prepared from WB and TW from seven elephants was screened for the presence of EEHV5 nucleic acid using a real-time quantitative polymerase chain reaction (qPCR) assay. Data for TW is expressed as VGC per test reaction and for WB as VGC per milliliter of blood. The y-axis on the graphs shows the quantity of EEHV5 genome copies, and the x-axis shows the number of days over which the study was conducted. Day 0 represents the first day that samples were collected (3 January 2011). Graphs for each animal’s WB and TW EEHV5 profiles are indicated. The time frame during which clinical signs were observed for elephant 1 is designated by the gray bar, and the duration of famciclovir treatment is indicated by a black bar.

Figure 3

Sequence comparison between the elephant endotheliotropic herpesvirus 5 (EEHV5) index case and two new strains. A. Sequence comparison of 904 base pairs (bp) from the index case DNA polymerase gene (U38/ POL) (see GenBank accession number JN983100), to the same locus from EEHV5 strain A found in elephants 1 and 3–6 (GenBank accession number JN983108.1) and EEHV5 strain B found in elephants 2 and 7 (GenBank accession number JX011012). B. Sequence comparison of 656 bp from the index case glycoprotein M gene (U71/ gM) (see GenBank accession number JN983105), to the same locus from EEHV5 strain A found in elephants 1 and 3–6 (GenBank accession number JN983113.1) and EEHV5 strain B found in elephants 2 and 7 (GenBank accession number JX011021). Sequences were aligned using ClustalW. Asterisks below the sequences indicate sequence identity. Bases highlighted in gray indicate sequence differences or deletions. The polymerase chain reaction (PCR) sequencing primers used for the U71/gM locus were the same as those used previously for EEHV1 strains, whereas those for the U38/POL locus were specific for EEHV5.