Persistent Low-Level Infections of Elephant Endotheliotropic Herpesvirus and Elephant Gammaherpesvus in Skin Nodules and Saliva from Wild and Zoo African Elephants

This study utilized a seven-year, multi-continental sampling of wild and zoo African and Asian elephants to detect persistent low-level infections of various known and novel Elephant Endotheliotropic and Gammaherpesviruses in skin nodules, saliva, and tissues, thereby significantly expanding the genetic library for elephant virology.

The Gist

The Big Picture: A Viral "Fingerprints" Project

Imagine elephants as a massive library of books. For a long time, scientists knew that some of these books contained dangerous chapters called EEHV (Elephant Endotheliotropic Herpesvirus). When these chapters get "loud" and active, they cause a deadly disease called Elephant Hemorrhagic Disease (EHD), which can kill an elephant in less than a day.

For years, there was a scary theory: Scientists thought that African elephants might be carrying these dangerous viruses and accidentally passing them to Asian elephants (who are more vulnerable), causing the Asian ones to get sick.

This study is like a massive detective investigation. The researchers went to Africa, the US, and zoos to collect "fingerprints" (DNA samples) from wild African elephants, forest elephants, and zoo elephants. They wanted to see exactly which viruses were hiding inside them and whether the African elephants were actually the "carriers" of the deadly Asian virus.

The Detective Work: How They Caught the Viruses

The team didn't just look at sick elephants; they looked at healthy ones too. They collected samples from three main places:

1. Saliva: Like swabbing a mouth to see what germs are hanging out there.
2. Skin Nodules: These are little bumps or lumps on the elephant's trunk or skin. Think of them as "virus hotels" where the germs are hiding.
3. Tissues: Samples from lungs or other organs.

They used a high-tech tool called PCR (think of it as a "molecular photocopier") to make millions of copies of any viral DNA found in the samples so they could read the genetic code.

The Big Discoveries

1. The "Safe" vs. "Dangerous" Virus Distinction

The researchers found a huge variety of viruses.

• The "Gammaherpes" (EGHV): These are like the "quiet neighbors." They live in the elephants' skin and saliva, but they rarely cause trouble. They are mostly harmless.
• The "Endotheliotropic" (EEHV): These are the "dangerous intruders." Some types (like EEHV1) are the ones that kill Asian elephants.

The Smoking Gun: The study found that African elephants do NOT carry the deadly EEHV1 virus that kills Asian elephants. They carry their own versions (EEHV2, 3, 6, 7, etc.).

• The Analogy: Imagine Asian elephants are allergic to "Peanut Butter" (EEHV1). The old theory was that African elephants were bringing the Peanut Butter into the room. This study proved that African elephants only bring "Almond Butter" (EEHV3, EEHV7, etc.). They are different ingredients entirely. So, African elephants aren't the culprits killing Asian elephants; the viruses are just species-specific.

2. The Skin Nodules are "Virus Mixtapes"

The researchers found something fascinating in the little bumps (nodules) on the elephants' skin.

• The Analogy: If you opened a single skin nodule, it wasn't just one virus hiding there. It was like a mixtape or a playlist containing 5 or 6 different virus strains playing at the same time.
• In fact, two different bumps on the same elephant could have completely different sets of viruses. It's as if the elephant's skin is a busy airport terminal where different viral "flights" are landing and taking off constantly.

3. The "Silent" Carriers

The study found that even healthy elephants who never got sick were carrying these viruses in their saliva and skin.

• The Analogy: Think of these viruses like dormant seeds in a garden. Most of the time, they are just sitting there quietly (low-level infection). They don't grow into weeds (disease) unless something triggers them.
• The researchers found that the amount of virus in a healthy elephant's saliva is tiny—like a few drops of water in a swimming pool. But in a sick elephant dying from EHD, the virus is like a fire hose. This means finding a tiny bit of virus in a healthy elephant does not mean they are sick; it just means they are a carrier.

4. Forest vs. Savannah Elephants

The study looked at two types of African elephants: the big Savanna elephants and the smaller Forest elephants.

• They found that Forest elephants (who live in the dense jungles of Gabon) carry a specific version of the virus (EEHV3B) that is slightly different from the Savanna elephants (EEHV3A).
• The Analogy: It's like two different dialects of the same language. The Forest elephants speak "Forest-EEHV" and the Savanna elephants speak "Savanna-EEHV." They can understand each other, but they have distinct accents.

Why Does This Matter?

This paper is a huge win for elephant conservation for three reasons:

1. No Blame Game: It clears the name of African elephants. We now know they aren't accidentally killing Asian elephants with a virus they don't even have.
2. Better Diagnosis: By knowing exactly what the "quiet" viruses look like, vets can stop panicking when they find a tiny bit of virus in a healthy elephant. They can now tell the difference between a "sleeping seed" and a "growing fire."
3. A New Library: The researchers created a massive digital library of these virus codes. This is like giving future scientists a map of the "virus territory," helping them develop better vaccines and treatments to stop the deadly outbreaks before they happen.

The Bottom Line

Elephants are living with these viruses naturally, just like humans live with cold viruses. Usually, the viruses stay quiet. This study proved that the deadly outbreaks in Asian elephants are caused by their own specific virus types, not by a cross-contamination from African elephants. The skin bumps and saliva are just the places where these viruses hang out, waiting, but usually, they stay harmless.

Technical Summary

1. Problem Statement

• Context: African (Loxodonta africana, Loxodonta cyclotis) and Asian (Elephas maximus) elephants are endangered. A major threat is Elephant Hemorrhagic Disease (EHD), a highly fatal condition caused by Elephant Endotheliotropic Herpesviruses (EEHV).
• Knowledge Gap: While EEHV types 1A, 1B, 4, and 5 are well-documented causes of fatal EHD in Asian elephants, the prevalence, diversity, and pathology of EEHV in wild African elephants were poorly understood.
• Hypothesis: There was a prevailing hypothesis that lethal EHD in Asian elephants might be caused by cross-species transmission from African elephants. Additionally, the nature of "skin nodules" (fibropapillomas) observed in wild African elephants was unknown; they were suspected to be related to herpesvirus infection but lacked genetic confirmation.
• Objective: To detect and characterize persistent, low-level infections of EEHV and Elephant Gammaherpesviruses (EGHV) in wild and zoo African elephants using skin nodules, saliva, and tissues, and to determine if cross-species transmission occurs.

2. Methodology

• Sample Collection:
  • Wild African Elephants (L. africana): Skin nodule biopsies, saliva, and lung tissues collected from 43 individuals across Kenya, Botswana, South Africa, and Zimbabwe. Samples included calves, sub-adults, and adults.
  • Wild Forest Elephants (L. cyclotis): Saliva swabs from 25 individuals in Gabon.
  • Zoo Elephants: Saliva collected over 7 years (2012–2019) from 7 wild-born L. africana at Six Flags Safari Park (USA), plus additional samples from 200 L. africana and 100 E. maximus in US zoos.
  • Specific Cases: Lung biopsies from a poached sub-adult female ("Enthusiasm") and skin nodules from a poached juvenile ("BW1M").
• Laboratory Techniques:
  • DNA Extraction: Performed using Qiagen kits with extended incubation. FFPE tissues were re-embedded and de-paraffinized prior to extraction.
  • Amplification: Conventional Polymerase Chain Reaction (cPCR) using a three-round nested primer strategy.
    • Primers targeted specific loci: U38 (POL), U39 (gB), U47 (gO), U66 (TER), U77 (HEL), U48.5 (TK), U51 (vGPCR1), U71 (gM), U73 (OBP), U81 (UDG), U82 (gL), and others.
    • Primers were designed to screen for known Loxodonta-associated EEHV/EGHV and to discover new species/subtypes.
  • Sequencing: Sanger sequencing of purified DNA from nearly all positive samples.
  • Controls: Rigorous negative controls and reagent testing were employed to prevent contamination, given the low viral load expected.

3. Key Contributions

• Discovery of Novel Viral Diversity: The study identified a vast library of EEHV and EGHV sequences, including:
  • Known Types: EEHV2, EEHV3A, EEHV3B, EEHV6, EEHV7A, and EGHV1B, EGHV2, EGHV3B, EGHV4B, EGHV5B.
  • Novel Types: Discovered new rare species/subtypes EEHV3C through EEHV3H and EEHV7B.
  • Novel Subtypes: Identified a novel subtype EGHV5A in a zoo E. maximus spleen.
• Resolution of Cross-Species Transmission: The study definitively showed that the primer sets used could detect Elephas-specific EEHV1A, 1B, 4, and 5, but none were found in the African elephant samples. This disproves the hypothesis that lethal EHD in Asian elephants is caused by cross-species infection from African elephants.
• Pathology of Skin Nodules: Confirmed that skin nodules in wild African elephants are sites of persistent, low-level herpesvirus infection, often harboring complex mixtures of viral genomes.
• Host Specificity: Demonstrated distinct host-specific lineages for EGHV (e.g., EGHV4A in Elephas vs. EGHV4B in Loxodonta) and suggested evolutionary divergence between EEHV3A (likely L. africana) and EEHV3B (likely L. cyclotis).

4. Key Results

• Prevalence in Skin Nodules:
  • 100% (n=10) of skin nodule/ear wart biopsies from wild L. africana were positive for low-level EEHV/EGHV DNA.
  • Co-infection: Nodules frequently contained mixed infections of multiple virus types (e.g., EEHV2, 3A, 3B, 6, 7A, 7B) and multiple subtypes simultaneously.
  • Intra-animal Variation: Different nodules on the same animal often harbored distinct viral strains and subtypes, suggesting high local diversity.
• Prevalence in Saliva:
  • Wild L. africana: 73% (29/40) of saliva samples were positive.
  • Wild L. cyclotis: 52% (13/25) were positive, predominantly for EEHV3 strains.
  • Zoo L. africana (Six Flags): 86% of the herd was positive for EEHV2, 71% for EEHV6, and 57% for EEHV3A/3B over the 7-year period.
  • Viral Load: Saliva samples required 2nd or 3rd round nested PCR to detect, indicating very low viral loads (hundreds to thousands of genome equivalents), contrasting with the high loads (millions) seen in acute EHD cases.
• EGHV Findings:
  • EGHV1B was the most abundant, with two distinct polymorphic variants (TTTT and CCGC) correlating with host species (L. africana vs. L. cyclotis).
  • EGHV3B was found in necropsy organs (heart, lymph nodes, thymus) of an asymptomatic zoo elephant, a rare finding for EGHV in internal tissues.
• Genetic Evolution:
  • EEHV3 strains showed significant chimeric domains (CDs) with up to 50% protein-level differences between subtypes, leading to the proposal of EEHV3C–H as distinct subtypes.
  • The study suggests EEHV3A and EEHV3B should be considered distinct species based on evolutionary divergence and host specificity.

5. Significance

• Diagnostic Implications: The study establishes that the presence of EEHV/EGHV DNA in saliva or skin nodules of asymptomatic elephants represents persistent low-level infection, not necessarily active, lethal systemic disease (EHD). This is crucial for distinguishing between healthy carriers and sick animals.
• Conservation Impact: By confirming that African elephants harbor their own distinct, endemic EEHV species (rather than being reservoirs for Asian elephant pathogens), the study refines conservation strategies and risk assessments for captive and wild populations.
• Virological Resource: The extensive sequence library (archived at the International Elephant Foundation) provides a critical reference for future studies on elephant virology, vaccine development, and understanding the evolution of herpesviruses in proboscideans.
• Methodological Advance: The successful use of non-invasive (saliva) and minimally invasive (skin nodule biopsy) sampling combined with nested PCR proves effective for monitoring viral persistence in wild populations where blood sampling is difficult or dangerous.

Conclusion: The paper concludes that persistent, low-level infections of diverse EEHV and EGHV species are endemic to both L. africana and L. cyclotis. These viruses exist in a state of latency or low-level shedding in healthy elephants, distinct from the acute, high-viremia state that causes fatal EHD. The study effectively rules out cross-species transmission from African to Asian elephants as the cause of Asian elephant EHD.