The pox virus occurs in seals. A virus in which seals get firm skin nodules on the head, neck and flippers, among other things. The pox usually goes away on its own. At the Sealcentre we do everything we can to prevent any contamination.

The pox virus in seals is a different species than the (chicken)pox virus that occurs in humans and belongs to the parapoxvirus family (1). But seals can transmit this virus to humans (2). To minimize the chance of this, our seal caretakers wear protective clothing, gloves and face masks.

The name of the virus refers to one of its most obvious features: pox. Pox are small firm skin nodules. They are between 1 and 3 centimeters in size and they can be all over the body (3). In seals we often see them on the head, neck and flippers.

Pox is a regular occurrence in seals in our sanctuary. This is because the disease is influenced by stress. It is unclear how seals contract the virus, but the seal already carries the virus before it is taken into care. We will only know this if the virus causes visible symptoms. If the seal is taken care of and gets stressed, the virus can 'express' itself, which means that after a while in the shelter, the seal will develop small firm skin nodules on its skin.

Pox is not contagious until it opens and bleeds out. To prevent a seal with the virus from infecting another seal, seals with pox are staying at the Sealcentre. They should not be released until the pox has disappeared, so that wild seals do not become infected.

Usually no treatment is needed. The pox goes away on its own over time, usually around 4-6 weeks. If a seal suffers from the pox virus, we can only treat the sympotms. If the seal is in pain, we administer painkillers. If the pox is infected with a bacteria, we treat it with antibiotics. In addition, we keep the pool water as clean as possible and it contains salt to keep wounds clean. After the pox has cleared, the seals are sometimes left with bald spots or scar tissue.

Sources:

1. Becher P, Konig M, Muller G, Siebert U, Thiel HJ (2002) Characterization of sealpox virus, a separate member of the parapoxviruses. Arch Virol 147: 1133–1140 DOI 10.1007/s00705-002-0804-8
2. Clark C, McIntyre PG, Evans A, McInnes CJ, Lewis-Jones S (April 2005). “Human sealpox resulting from a seal bite: confirmation that sealpox virus is zoonotic”.  J. Dermatol. 152 (4): 791–3. doi:10.1111/j.1365-2133.2005.06451.x. PMID 15840117. S2CID 38466772.
3. Sealpox Virus in Marine Mammal Rehabilitation Facilities, North America, 2007–2009 Amira A. Roess,1 Rebecca S. Levine, Laura Barth, Benjamin P. Monr oe, Darin S. Carroll, Inger K. Damon, and Mary G. Reynolds. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 12, December 2011

The herpes virus that seals can carry is not the same herpes virus that we humans can get. It is a highly contagious virus, which is why we are doing everything we can to prevent any spread in the Sealcentre.

Herpes is a virus that seals carry for the rest of their lives after infection. This virus is not the same herpes virus that humans can get. There are seven variants of this phocine herpesvirus (PhHV).

Did you know...

We think it is very special that our head veterinarian Ana Rubio García belongs to the group of scientists who discovered this seventh variant in 2014 (1). When seals in our rehabilitation centre carry herpes, it is almost always this seventh species.

Herpes is not clearly visible by one specific complaint or change in appearance. Seals can have several complaints at the same time. Possible symptoms of herpes viruses are:

• Runny nose (often with blood)
• Inflamed oral mucosa
• Vomiting
• Diarrhea
• Fever
• Cough
• Pneumonia
• Hair loss in grey seals (2)

Herpes remains in the seal's body forever. As a result, the complaints can occasionally return. Something similar happens in humans as well. The cold sore, an irritated blister that some people get around the mouth, is a characteristic of the herpes virus (herpes labialis). If you become infected with the cold sore, you will keep this virus with you for the rest of your life (3). In case of stress or fever, you can regularly get a cold sore again, which always disappears over time.

Herpes is a highly contagious disease. Seals can transmit it to each other through virus particles in the air. That is why it is very important to immediately separate a seal with herpes from the other seals in the sanctuary, by placing them in separate enclosures.

There is no cure for herpes. We do try to counteract the symptoms of the virus, for example by lowering the fever with medication. We can also treat the inflamed oral mucosa by giving mouthspray. As soon as the seal no longer has any symptoms, it is no longer contagious. The animal can then stay with other seals and eventually be released.

Sources:

1. Bodewes R, Contreras GJS, García AR, Hapsari R, van de Bildt MWG, Kuiken T, Osterhaus ADME. Identification of DNA sequences that imply a novel gammaherpesvirus in seals. J Gen Virol. 2015;96(Pt 5):1109–14.
2. Field, C. L. (2022, 7 juli). Viral diseases of marine mammals. MSD Veterinary Manual. Geraadpleegd op 30 juni 2022, van https://www.msdvetmanual.com/exotic-and-laboratory-animals/marine-mammals/viral-diseases-of-marine-mammals
3. Herpes labialis (koortslip) | RIVM

There are four types of influenza in total. Types A, B and C cause flu in humans. Influenza types A and B can occur in marine mammals, such as in seals. Influenza can cause a huge wave of disease in wild seals.

There are four types of influenza in total. Types A, B and C cause flu in humans. Influenza types A and B can occur in marine mammals, such as in seals. Influenza can cause a huge wave of disease in wild seals.

Influenza is not clearly visible by one specific complaint or change in appearance. Seals can have several complaints at the same time. The characteristics of influenza B are unknown. Possible features of influenza A are:

• Weakness
• Bad coordination
• Short of breath
• Swollen neck
• White or bloody runny nose
• Pneumonia

The virus droplets are spread by, among other things, coughing and sneezing, and are then inhaled again. Influenza is extremely contagious. Not only for seals, but also for humans. That is why it is very important to protect both the seals and ourselves if someone is carrying the virus.

Common and grey seals can be sick with influenza. It is shown that mainly common seals suffer from the influenza virus. In several major outbreaks of the virus, mainly common seals died. The last outbreak of influenza was in 2014, when thousands of common seals washed up dead on the coasts of the Netherlands, Germany, Denmark and Sweden (1).

Seals can also get influenza from birds. In October 2015, the avian flu virus (H10N7) was the cause of major deaths among harbor seals (2). Seals probably contracted the virus through direct or indirect contact with wild birds or their faeces.

In June 2022, researchers found the avian flu virus in three seals in Germany, but it hasn't sparked a massive outbreak. The fact that the virus is transferred from a bird to a marine mammal means that there is a chance that humans can also be infected.

It is not possible to cure influenza. There is no medicine for this virus. We can only try to reduce the symptoms and wait until the seal gets better.

Sources:

1. Bodewes R, Rubio García A, Brasseur SM, Sanchez Conteras GJ, van de Bildt MWG, Koopmans MPG, et al. (2015) Seroprevalence of Antibodies against Seal Influenza A(H10N7) Virus in Harbor Seals and Gray Seals from the Netherlands. PLoS ONE 10(12): e0144899. doi:10.1371/journal. pone.0144899

1. Zohari S, Neimanis A, Härkönen T, Moraeus C, Valarcher JF. Avian influenza A(H10N7) virus involvement in mass mortality of harbour seals (Phoca vitulina) in Sweden, March through October 2014. Euro Surveill. 2014;19(46):pii=20967. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20967 

• Laura Verga, Marlene G. U. Sroka, Mila Varola. Stella Villanueva and Andrea Ravignani. (2022). Spontaneous rhythm discrimination in a mammalian vocal learner. Biology Letters, 18:20220316https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2022.0316

• David Ebmer, Stephan Handschuh, Thomas Schwaha, Ana Rubio‑García, Ulrich Gärtner, Martin Glösmann, Anja Taubert and Carlos Hermosilla. (2022). Novel 3D in situ visualization of seal heartworm (Acanthocheilonema spirocauda) larvae in the seal louse (Echinophthirius horridus) by X-ray microCT. Scientific Reports, 12:14078  https://www.nature.com/articles/s41598-022-18418-y

• Anna Salazar-Casals; Koen de Reus; Nils Greskewitz; Jarco Havermans; Machteld Geut; StellaVillanueva; Ana Rubio-Garcia. Increased Incidence of Entanglements and Ingested Marine Debris in Dutch Seals from 2010 to 2020. (2022) Oceans, Vol 3, Issue 3, 389-400. https://doi.org/10.3390/oceans3030026

• Jörg Hirzmann, David Ebmer, Guillermo J. Sánchez‑Contreras, Ana Rubio‑Garcia, Gerd Magdowski, Ulrich Gärtner, Anja Taubert and Carlos Hermosilla. The seal louse (Echinophthirius horridus) in the Dutch Wadden Sea: investigation of vector-borne pathogens (2021) Parasites & Vectors 14:96 https://doi.org/10.1186/s13071-021-04586-9

• Abbo van Neer, Ana Rubio-Garcia , Stephanie Gross, Anna Salazar-Casals, Alberto Arriba-Garcia2 Peter Wohlsein and Ursula Siebert. An innovative approach for combining marking of phocid seals with biopsy sampling using a new type of livestock ear tags. (2020) Journal of Marine Animals and Their Ecology Vol 12, Issue 1, 2020.

•Anna Salazar-Casals, Klaas Marck, Tijmen de Jong, James Collins, Joost Dorgelo, Pier Prins, and Ana Rubio-Garcia Retrospective study of surgical treatment of refractive osteomyelitis and infectious arthritis in the flippers of seals in The Netherlands. (2020) Journal of Zoo and Wildlife Medicine 51(3), 598-605, (16 November 2020). https://doi.org/10.1638/2018-0221

• Anna Salazar-Casals, Alberto Arriba-Garcia, Antonio A. Mignucci-Giannoni, John O’Connor, Ana Rubio-Garcia. Hematology and serum biochemistry of harbor seal (Phoca vitulina) pups after rehabilitation in the Netherlands (2020) J. of Zoo and Wildlife Medicine, 50(4):1021-1025 https://doi.org/10.1638/2018-0098

• Rubio-Garcia, A., Rossen, JWA., Wagenaar, JA., Friedrich, AW., van Zeijl, JH. Livestock-associated meticillin-resistant Staphylococcus aureus in a young harbour seal (Phoca vitulina) with endocarditis (2019) Veterinary Record Case Reports 7: e000886. https://doi.org/10.1136/vetreccr-2019-000886

• Ravignani A, Kello CT, de Reus K, Kotz SA, Dalla Bella S, Méndez-Aróstegui M, Rapado-Tamarit B, Rubio-Garcia A, de Boer B. Ontogeny of vocal rhythms in harbor seal pups: an exploratory study (2019) Current Zoology, Volume 65, Issue 1, Pages 107–120, https://doi.org/10.1093/cz/zoy055

• Maarten J. Gilbert*, Aldert L. Zomer, Arjen J. Timmerman, Mirlin Spaninks, Ana Rubio-Garcia, John Rossen, Birgitta Duim, and Jaap A. Wagenaar. Campylobacter blaseri sp. nov., isolated from common seals (Phoca vitulina) (2018) International Journal of Systematic and Evolutionary Microbiology. DOI 10.1099/ijsem.0.002742 https://library.wur.nl/WebQuery/wurpubs/537778

• Ravignani A*, Gross S*, Garcia M, Rubio-Garcia A, de Boer B. How small could a pup sound? The physical bases of signalling body size in harbour seals. (2017) Current Zoology, 2017, 1–9. Doi: 10.1093/cz/zox026 https://academic.oup.com/cz/article/63/4/457/3603549

• Ulrich SA, Lehnert K, Rubio-Garcia A, Sanchez-Contreras GJ, Strube C, Siebert U. Lungworm seroprevalence in free-ranging harbour seals and molecular characterisation of marine mammal MSP. (2016) International journal for parasitology: parasites and wildlife. Doi:10.1016/j.ijppaw.2016.02.001 https://www.sciencedirect.com/science/article/pii/S2213224416300062

• Bodewes R*, Rubio García A*, Brasseur SM*, Sanchez Conteras GJ, van de Bildt MWG, Koopmans MPG, Albert D. M.E. Osterhaus, Thijs Kuiken. Seroprevalence of Antibodies against Seal Influenza A(H10N7) Virus in Harbor Seals and Gray Seals from the Netherlands. (2015) PLoS ONE 10(12): e0144899. doi:10.1371/journal. pone.0144899 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144899

• Rubio García A, Sánchez Contreras GJ, Juliá Acosta C, Lacave G, Prins P, Marck K. Surgical treatment of osteroarthritis in harbor seals (Phoca vitulina).(2015) Journal of Zoo and Wildlife Medicine 46(3):553-559. http://www.bioone.org/doi/abs/10.1638/2014-0229.1

• Woodman S, Gibson A.J, Rubio Garcia A, Sanchez Contreras G, Rossen J.W, Werling D, Offord V. (2015) Structural characterisation of Toll-like receptor 1 (TLR1) and Toll-like receptor 6 (TLR6) in elephant and harbor seals. Veterinary Immunology and Immunopathology 169, DOI: 10.1016/j.vetimm.2015.11.006 https://www.sciencedirect.com/science/article/pii/S0165242715300210

• Bodewes R, Sánchez Contreras GJ, Rubio García A, Hapsari R, van de Bildt MWG, Kuiken T, Osterhaus ADME. (2015) Identification of DNA sequences that imply a novel gammaherpesvirus in seals. Journal of General Virology, 96, 1109–1114 DOI 10.1099/vir.0.000029 http://jgv.microbiologyresearch.org/content/journal/jgv/10.1099/vir.0.000029

• Reichel M, Muñoz-Caro T, Sánchez Contreras GJ, Rubio García A, Magdowski G, Gärtner U, Taubert A, Hermosilla C. (2015) Harbour seal (Phoca vitulina) PMN and monocytes release extracellular traps to capture the apicomplexan parasite Toxoplasma gondii. Developmental and Comparative Immunology (2015), doi: 10.1016/j.dci.2015.02.002 https://www.sciencedirect.com/science/article/pii/S0145305X15000257

• Bodewes R, Hapsari R, Rubio García A, Sánchez Contreras GJ, van de Bildt MWG, de Graaf M, Kuiken T, Osterhaus ADME. (2014) Molecular epidemiology of seal parvovirus, 1988-2014. PLoS ONE 9(11): e112129. doi:10.1371/journal.pone.0112129 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0112129

• Bodewes R, Rubio García A, Wiersma LCM, Getu S, Beukers M, Schapendonk CME, van Run PRWA, van de Bildt MWG, Poen MJ, Osinga N, Sánchez Contreras GJ, Kuiken T, Smits SL, Osterhaus ADME. (2013) Novel B19-Like Parvovirus in the Brain of a Harbor Seal. PLoS ONE 8(11): e79259. doi:10.1371/journal.pone.0079259 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079259

• Bodewes R, Morick D, van de Bildt MWG, Osinga N, Rubio García A, Sánchez Contreras GJ, Smits SL, Reperant LAP, Kuiken T & Osterhaus ADME. (2012). Prevalence of phocine distemper virus antibodies: bracing for the next seal epizootic in north-western Europe. Emerging Microbes and Infections (2013) 2, e3; doi:10.1038/ emi.2013.2 https://www.nature.com/articles/emi20132

Grey seals and Common seals are apparently part of a very specific group of animals. Animals that, just like humans, have the ability to develop their voice over the course of their life. This phenomenon is called ‘vocal learning’. Other animals that possess this ability are parrots, passerine birds, and bats. An extraordinary example of vocal learning in seals is a seal called Hoover, who was kept in Boston’s New England Aquarium. Hoover was raised by humans and learned to copy human speech. Andrea Ravignani did his postdoctoral research at the Sealcentre and investigated the ‘crying’ of seal pups.

Read more about his research group.

Andrea Ravignani is doing postdoctoral research at Sealcentre Pieterburen that is funded by the prestigious Marie Curie Scholarship. Andrea is an Italian scientist who is fascinated by the question of how animals – and humans – learn to produce sounds. As a part of his research in Pieterburen, he records the sounds of seal pups every day; the so-called ‘crying’. Andrea uses these recordings to then see if there is a development in the production of these sounds.

Have you ever noticed how babies (human pups) begin with crying, then transition to incoherent babbling, and how this slowly changes into language? Something similar happens in seals. The sound – or voice – of each seal is very different, and their voices also change as they age. In fact, it looks like Grey and Common seals are members of a special group of animals that, like humans, have the ability to shape their voices over the course of their lives. This ability is called ‘vocal learning’. Other animals that have this ability are parrots, passerine birds and bats.

An exceptional example of this ability in seals is the aforementioned seal named Hoover. Hoover was an orphaned pup who was taken in and raised by humans in Boston. Before he was relocated to the New England Aquarium, he had learned to mimic human speech. Hearing Hoover speak his former owner’s catchphrases is truly bizarre. You can hear how he sounds in the YouTube video “Hoover the Talking Seal”. Seals learn to make sounds through imitation, which they then adapt and change into their very own voice. Because of that, they might be the animal closest to us humans when it comes to ‘vocal learning’.

Andrea’s research is important for two reasons. On the one hand it helps us to gain a better understanding of seals and what is important for them in the first phases of their life. On the other hand it gives us a glimpse into the evolution of humans. Human evolution is very difficult to reconstruct without a time machine, especially when it comes to the evolution of speech and language. Communication in seals is a completely new field of study.

In December 2018, Dr Andrea Ravignani published his discovery that seal pups adjust their communication based on the sounds of other pups. A sense of rhythm and timing had never before been demonstrated in seals. His work gives an insight into the vocal communication of humans, as well as seals.

Research conducted by Dr Andrea Ravignani from the Artificial Intelligence Lab of the Vrije Universiteit Brussel at Sealcentre Pieterburen was the first to show that seal pups exhibit complex communication behaviour. He observed that seal pups adjust their sounds and especially their rhythm to what another pup is doing. Said simply: they take turns making sounds. However simple this may seem, it has never before been demonstrated in seals and it characterises animals that use complex communication methods. The study will be published in the Journal of Comparative Psychology.

Ravignani: “Us humans often consider our communication to far more complex than that of other animals. However, what we are seeing in seal pups is astonishing. Even at four weeks old, seals seem to demonstrate a very precise and flexible timing in their communication. To an extent this is very comparable to the alternation we see in human conversations or in a musical canon.”

The discovery fits in well with a study conducted by the Sealcentre into the behaviour of mothers and pups in the wild, which showed that pups suckle with several different mothers. It is therefore important that pups stand out between their peers and adjust their calls.

Ravignani: “This finding was relatively unexpected and even seems counterintuitive at first. Communication in Common seals is usually relatively vertical – between mother and pup, not between different pups. However, what we see here is horizontal communication: the rhythm of one pup determines the rhythm of another pup. While this is surprising within the established knowledge of mother-pup interactions in Common seals, my findings fit very well in the behavioural research that the Sealcentre is conducting with the University of Groningen.”

The study is part of a two-year research programme that Ravignani is conducting with the support of the Marie Curie Scholarship.

Seals are good at learning sounds. The 'talking seal' Hoover could even imitate human speech. But can young seals already adapt their sounds to the environment? Researchers from the Max Planck Institute for Psycholinguistics, the Vrije Universiteit Brussel and the Pieterburen Seal Centre studied seal pups a few weeks old. When the seal pups heard louder ambient sounds, they themselves called out with a lower pitch. This makes seals very suitable for research into the evolution of human speech.

The seal Hoover had been taken in as a pup by an American family. Even after he had already been moved to an aquarium, he continued to mimic human speech: he barked at visitors in his gruff voice (“Come over here”). Seals therefore belong to the small group of mammals that can learn to imitate sounds, also called 'vocal learning'.

It is even more special if animals can adjust the pitch of their voices: an important feature of human speech. Senior researcher Andrea Ravignani says: "By studying these extraordinary mammals, we hope to eventually better understand how humans evolved speech and why we ourselves are such a talkative species." What Ravignani and his colleagues particularly wanted to know: could seals adjust their pitch from an early age?

Sounds of the Wadden Sea

The researchers decided to study eight seal pups from 1 to 3 weeks old. The seals were already staying at seal centre Pieterburen to gain strength. After 2-3 months in the sanctuary, they were released into the wild. To investigate whether the seal pups could adapt their sounds to ambient noise, the biologists first made recordings of natural ambient sounds of the Wadden Sea. These sounds were played in the seals' enclosure for a few days, at three different sound levels (from no sound to 65 dB). The pitch of the ambient sounds was similar to that of the seal sounds. The researchers also made recordings of the seal sounds. Would the pups adapt to the ambient noise and call higher or lower?

When ambient sounds were louder, the seals called with a lower pitch. At the loudest sounds, their pitch also remained the most stable. One seal also clearly showed the 'Lombard' effect: it started calling louder when ambient sounds were louder. This effect is also typical of human speech: people start talking louder when there is ambient noise, so they can be better understood. But the seals did not call out more often or longer at different noise levels.

Brain pathways

So even very young seals can already adapt their sounds to the environment by calling at a different pitch. That ability they share with humans and bats is unusual for a mammal. Other animals only call louder in similar experiments.

"The seal pups have much better control over their vocalisations than we thought,", says Ravignani "And they already have control over their voice when they are only a few weeks old. That is unique in the animal world. We thought only humans had a direct connection between the cerebral cortex and the larynx. But seals therefore seem to have these connections too. That brings us another step closer to unravelling the mystery of human speech."

Veterinarian and researcher at seal centre Pieterburen Anna Salazar Casals added: "As a rehabilitation centre, we are happy to collaborate on research, in order to understand the animals better and protect them even better. We can use these new insights, for example, when setting up new shelter facilities or determining what resting areas in the wild should comply with."

Seals are good at learning sounds. The 'talking seal' Hoover could even imitate human speech. But can young seals already adapt their sounds to the environment? Researchers from the Max Planck Institute for Psycholinguistics, the Vrije Universiteit Brussel and the Pieterburen Seal Centre studied seal pups a few weeks old. When the seal pups heard louder ambient sounds, they themselves called out with a lower pitch. This makes seals very suitable for research into the evolution of human speech.

Most animals make sounds that fit their body size. A larger animal will sound lower because the larynx is longer: the air-filled canal in the neck where the vocal cords are located. But seals do not always sound the way they look. Sometimes they sound lower and therefore bigger, for example to impress a rival. Or higher and thus smaller, for instance to get more attention from their mother. Are these animals good at learning sounds (vocal learning) or has their larynx adapted to be more flexible?

Sealcentre Pieterburen

To answer this question, PhD student Koen de Reus and senior researcher Andrea Ravignani from the MPI worked with researchers from Sealcentre Pieterburen. The team measured the larynxes and body size (length and weight) of 68 young seals (up to 12 months old) that had died before or after a rescue attempt. The researchers also analysed previously recorded seal sounds, confirming the seal's wide range in pitch.

De Reus and Ravignani found that the length of the seal larynx matched their body size exactly. So there were no anatomical explanations for their vocal talents. According to the researchers, only the vocal learning ability of seals can explain why they do not always sound the way they look.

Vocal learning ability

"Animals with vocal learning ability will sound differently than expected based on their body size, but the length of their larynx matches their body size. This combined acoustic and anatomical data can help us find more animals like this,", says de Reus "Studying multiple animal species with this ability is also going to help us find the biological basis of vocal learning. And possibly it will also provide insights into the evolution of complex communication systems such as speech.".

"The more we study seals, the more we see that they can tell us something about human speech,", Ravignani adds.