Surviving and fatal Elephant Endotheliotropic Herpesvirus-1A infections in juvenile Asian elephants - lessons learned and recommendations on anti-herpesviral therapy

Abstract

Background: Elephant Endotheliotropic Herpesviruses (EEHVs) can cause acute haemorrhagic disease in young Asian elephants (Elephas maximus) and clinical EEHV infections account for the majority of their fatalities. The anti-herpesviral drug famciclovir (FCV) has been used routinely to treat viraemic at-risk elephants, but thus far without proven efficacy. This paper presents clinical and virological investigations of two EEHV-1A infected elephants treated with FCV, and discusses anti-herpesvirus therapies of viraemic elephants.

Cases presentations: Two 1.5 year old male Asian elephants at a zoological collection in the UK developed clinical EEHV-1A infections. Case 1 showed signs of myalgia for the duration of 24 hours before returning back to normal. EEHV-1A DNAemia was confirmed on the day of clinical signs and continued to be present for 18 days in total. Trunk shedding of the virus commenced 10 days after detection of initial DNAemia. Case 2 tested positive for EEHV-1A DNAemia in a routine blood screening sample in the absence of clinical signs. The blood viral load increased exponentially leading up to fatal clinical disease seven days after initial detection of DNAemia. Both calves were treated with 15 mg/kg FCV per rectum on detection of DNAemia and penciclovir, the FCV metabolite, could be detected in the blood at assumed therapeutic levels. The early indicators for clinical disease were a marked absolute and relative drop in white blood cells, particularly monocytes prior to the detection of viraemia. The most prognostic haematological parameter at later stages of the disease was the platelet count showing a continuous sharp decline throughout, followed by a dramatic drop at the time of death.

Conclusions: The EEHV-1A viraemic animals investigated here further highlight the ongoing threat posed by these viruses to juvenile Asian elephants. The findings call into question the efficacy of rectal FCV in clinical cases and direct towards the use of alternative anti-herpesvirus drugs and complementary treatments such as plasma infusions if no improvement in either viral load or the above-mentioned blood parameters are observed in the initial days of viraemia despite anti-herpesvirus therapy.

Keywords: EEHV-1; EEHV-HD; EEHV-haemorrhagic disease; elephantid herpesvirus; famciclovir; ganciclovir.

Fig. 1

EEHV-1A DNA levels in blood and trunk secretions of Case 1. Clinical suspicion of EEHV infection was confirmed by detection of EEHV-1A DNA in blood. The animal showed clinical signs suggestive of active EEHV-1A infection on Day 0 and Day 1. EEHV-1A DNA load in EDTA whole blood (solid line) and trunk secretions (dashed line) was measured using a qPCR

Fig. 2

Nucleotide sequence comparison of the EEHV-1A detected. Partial nucleotide sequences of DNA polymerase [U38/POL (194 bp)], glycoprotein L [U82/gL (381 bp)] and glycoprotein M [U72/gM (500 bp)] from Case 1 and Case 2 were compared with those of two previous EEHV-1A fatalities (Riddle and Betts) from the same zoological collection. Sequences were aligned using the MegAlign 13 software of the DNASTAR Lasergene 13 package (DNASTAR Inc. Madison, USA). Identical nucleotides to those of Case 1 are denoted by dots in the alignments

Fig. 3

Penciclovir, the metabolite of famciclovir, plasma levels in 2 juvenile Asian elephants with EEHV-1A DNAemia. Famciclovir (FCV) was rectally administered in Case 1 at 15 mg/kg twice daily (BID) on observation of clinical signs indicative of EEHV-1A infection (Day 0) and continued at the same dose rate until Day 1, when it was reduced to 12 mg/kg thrice daily (TID). This was followed by further reduction on Day 3 to 8 mg/kg BID and continued unchanged until Day 18. In Case 2 FCV was administered at 15 mg/kg TID for two days following the detection of EEHV-1A DNA in the blood (Day -5), five days prior to observation of EEHV-1A clinical signs, and continued at the same dosage till the last dose of FCV at 9:00 am on Day 0; blood was only collected at 17:00 pm on that day. The death of Case 2 was at midnight on Day 1; seven days after first detection of EEHV-1 DNA in the blood. Dashed line indicates the minimum level of PCV considered therapeutic in humans with genital herpes (>100 ng/ml) [27]