| The Question: I recently read that sharks are immune to all disease. Is this true? Submitted by: Marion F., Somerville, MA |
The Short Answer: No, it’s not true. Sharks get bacterial infections, viral infections [see comments], and they suffer from parasites, in short, the enti
re suite of infectious diseases from which all animals and plants must protect themselves. Sharks also get cancer, contrary to another widely disseminated myth.
More Info: The claim that sharks don’t get disease or suffer from cancer is mostly spread by advertisements for shark cartilage as a dietary supplement. These supplements claim to prevent disease or cure cancer, but none has ever been shown in rigorous medical tests to protect people from disease. Tumors rarely infiltrate into cartilage, in any vertebrate whether a shark or a person, and cartilage seems to have some ability to inhibit the growth of blood vessels. Since a growing tumor needs blood vessels to continue to expand, there have been attempts to develop “antiangiogenic” drugs that fight cancer by limiting growth of new capillaries. Ground cartilage, whether from sharks or cows, shows some antiangiogenic effect in the laboratory, but has not shown any benefit in actual people. But shark cartilage sellers have connected the fact that the skeleton of a shark is entirely made of cartilage with the antiangiogenic properties of cartilage to claim that this protects sharks from cancer. It just isn’t true. The truth is that while we do know for certain that sharks get diseases and cancer, we don’t know at what rate. Sick sharks probably get eaten or fall to the bottom of the ocean to decompose. They would rarely be available to be counted. Sharks that are harvested by fisherman do occasionally show infectious disease or cancers. No one has done a comprehensive survey of sharks to know whether they have high or low rates of illness. Even if sharks are particularly free from disease, that wouldn’t necessarily mean shark cartilage has any value as a treatment for human disease. And the tests that have been done have not shown any value over a placebo. 
The Interesting Science: The immune system of sharks is very much like ours. We have what’s called the “innate immune system” which is somewhat hardwired to fight generalized intruder microorganisms and parasites. The innate immune system can respond over long periods of time through the mechanism of natural selection to adapt to new diseases. We also have an “adaptive immune system” (also called the “acquired immune system”) that adapts in real time to new intruders. This is the familiar system of antibodies and white blood cells that gets the most discussion in terms of diseases such as flu, the common cold, and AIDS. It was once thought that vertebrates like sharks, bony fish, amphibians, reptiles, birds, and mammals were the only animals that had an adaptive immune system. But recent discoveries have shown that lampreys and hagfish, fish that split off onto their own evolutionary branch early in the history of vertebrates, have a different system of generating antibodies and adapting to fight new viral and bacterial threats. And it appears that 
other animals from snails to fruit flies may also have adaptive immune systems that work differently from ours, but accomplish the same goal of recognizing and attacking new microbes and viruses.
The Environmental Message: Shark populations are plummeting around the globe, in large part due to fishing for shark fin for shark fin soup, and for cartilage for shark cartilage supplements. As top of the food chain predators, shark numbers have never been as high as a fish like cod. Sharks also reproduce slowly. Unlike a cod, which can lay millions of eggs, many sharks lay only a few hundred in the average lifetime. What this means is that harvesting sharks is generally not sustainable. There aren’t enough of them to start with, and they can’t rebuild their populations rapidly.
References:
Shark Cartilage, Cancer and the Growing Threat of Pseudoscience. Ostrander GK, Cheng KC, Wolf JC and Wolfe MJ. Cancer Research, 64, 8485-8491, 2004.
Evaluation of shark cartilage in patients with advanced cancer: a North Central Cancer Treatment Group trial. Cancer, Jul 1;104(1):176-82. 2005.
Added in Dec. 2013: First reports of proliferative lesions in the great white shark, Carcharodon carcharias L., and bronze whaler shark, Carcharhinus brachyurus Günther. R. Robbins, B. Bruce, A. Fox, Nov. 2013, Journal of Fish Diseases.
I am curious to know the source that permits you to conclude that sharks are subject to viral infections
Hi, sorry it took so long to respond to this comment.
I’m having trouble finding confirmation that sharks get viral infections. I may have extrapolated that. However, there is a great deal of research going on about the substance squalamine isolated from sharks, which has anti-viral properties. The very fact that sharks produce a powerful anti-viral compound is strong evidence that they fight against viral infection. The ocean is swimming with viruses and there’s no reason to suspect that sharks would be the one type of organism on earth that is immune to viruses.
There have been very few studies of the health status of wild sharks. Most likely, if we did such a study, we’d find that most sharks don’t have viral infections and a few do … just like every other animal in the world. It may be that sharks have developed a neat anti-viral trick and are therefore less susceptible to viral infection than other organisms. But viruses are so adaptable, I would be very surprised if viruses haven’t found ways around squalamine and probably the sharks are in a constant arms race with their viruses just as we are.
If you picked out five people randomly out of a crowd, probably none of them will be exhibiting signs of viral infection. We wouldn’t conclude from that that people are immune to viruses, but that’s what people seem to do with sharks.
Just noticed a new report on cancer in wild great white sharks (Carcharodon carcharias) and bronze whaler sharks (Carcharhinus brachyurus).
First reports of proliferative lesions in the great white shark, Carcharodon carcharias L., and bronze whaler shark, Carcharhinus brachyurus Günther. R. Robbins, B. Bruce, A. Fox, Nov. 2013, Journal of Fish Diseases.
The claim that sharks don’t get disease or suffer from cancer is mostly spread by advertisements for shark cartilage as a dietary supplement? See: Sharks, Dinosaurs, Ferromagnetic Cancer Theory and Father of Oncology. Dinosaurs and other reptiles roamed the Earth in the past. Many dinosaurs had cancer, researchers have discovered. Ancient humans could have contracted cancer just as much as people do today. Humans kill about 100 million sharks per year. Researchers have known for more than 150 years that sharks get cancer. There is no scientific evidence that shark cartilage is useful in treating or preventing cancer. Cancers have been found in everything from coral to budgerigars. The interaction of many factors together produces cancer. Modern humans know that primary tumors develop at body sites of excessive iron deposits. There are no exceptions: body sites affected by primary tumors are iron-rich body sites. When tumor cells metastasize, the new tumor is called a secondary or metastatic tumor, and its cells are similar to those in the primary tumor. If breast cancer metastasizes to the lungs, the secondary tumor is made up of abnormal breast cells, not of abnormal lung cells. Misplaced iron created primary tumors in dinosaurs and ancient humans; misplaced iron creates primary tumors in corals, sharks, budgerigars and modern humans. The Father of Oncology (Vadim Shapoval) says that a cell needs to have iron overload (when excess iron accumulates within cellular organelles) before it becomes cancerous. In inherited forms of cancer, parents give their sons and daughters abnormal iron metabolism within various organs. Iron disorders are inherited and can be confirmed with genetic testing. Genes that maintain iron homeostasis may facilitate iron uptake, storage or egress, or the regulation of any of these processes. The spectrum of known disorders of iron metabolism has expanded dramatically over the past years. Any cancer is caused by iron-related genes (numerous genes directly/indirectly involved in iron metabolism / hereditary cancers) and iron-related events (when excess iron accumulates within the cells, tissues, and organs due to various carcinogenic lifestyle events / sporadic cancers). Genes load the gun, the environment pulls the trigger. The structure and physical properties of any cell must ultimately be described by the known laws of chemistry and physics. According to the Ferromagnetic Cancer Theory (Theory from the Old Testament; Iron Conception), any human cell should be interpreted: 1) as a society of atoms and molecules; 2) as a society of organelles; 3) as a society of dia-, para-, superpara-, ferri- and ferromagnetic nanoparticles that have certain local magnetic contacts. Cancer occurs through excessive accumulation of superpara-, ferri- and ferromagnetic nanoparticles within cancerous cells. Intracellular molecules FeO;Fe2O3;Fe3O4 are the main creators of intracellular superpara-, ferri- and ferromagnetic nanoparticles that produce (magnetically) genomic rearrangements, chaotic chromosomal aberrations and chromothripsis within cancerous cells. Any cancer is a subtle iron disease; a form of iron lottery; intracellular superpara-ferri-ferromagnetic infection. Magnetism (a class of physical phenomena; the force of attraction or repulsion between nano-objects) causes cancer. Ceramic needles (direct intratumoral injections) can suppress/eliminate any tumors and large metastases; can quickly create harmless infiltrations (harmless necroses; deposits of cells that die; benign capsules); can enter solution [sulfur (2%) + olive oil (98%); 36.6C – 39.0C] or water containing hydrogen sulfide to tumors and large metastases. Anti-iron slow blood loss (even 75%) [hemoglobin control], anti-iron goat’s milk diet and anti-iron drinking water containing hydrogen sulfide can neutralize any micro-metastases and isolated cancerous cells. Vadim Shapoval (Father of Oncology) http://www.medicalnewstoday.com/opinions/174294 ; http://www.livescience.com/41655-great-white-shark-cancer.html ; http://www.ovarian-cancer-facts.com/ovarian-tumor.html ; http://healthland.time.com/2013/04/01/the-conspiracy-to-end-cancer/ ; http://animals.howstuffworks.com/fish/sharks/shark-cure-cancer.htm ; http://www.scientificamerican.com/article/sharks-do-get-cancer-tumor-found-great-white/ ; http://www.buzzle.com/articles/shark-cartilage-and-cancer-cure.html ; http://news.discovery.com/animals/sharks/sharks-do-get-cancer-tumor-found-in-great-white-131205.htm ; http://askanaturalist.com/are-sharks-immune-to-disease-and-cancer-2/ ; Together We (Ask a Naturalist.com, Discovery Communications, Buzzle, Scientific American, HowStuffWorks, LiveScience, Ovarian Cancer Facts, Merriam-Webster, YouTube, News-Medical.Net, Medical News Today, The Scientist, TIME, Google, Facebook, VK and Vadim Shapoval) Will Beat Cancer