PARASITES AND MASS STRANDED WHALES
by Captain David Williams
Deafwhale Society, Inc
PO Box 319, Dumaguete City
6200 Oriental Negros
Philippines
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PARASITIC WORM INFECTIONS
Besides shark and killer whale attack and the lack of food and fresh water due to the inability to dive, the pod's greatest detriment to recovery would be the rapid unsettling of the symbiotic relationship each whale has with its parasites.
A healthy whale's immune system allows a few parasitic worms to reside in each of the sinus cavities. These worms keep the sinuses clean by feeding on mucus, blood, body fluids, and loose tissue. In exchange, the whale provides food and a safe environment for the parasites to live.
Parasitic worms lay hundreds of eggs in the sinus cavity walls where they may remain for many years, prevented from hatching by the whale's immune response. Severe stress coupled with no food or fresh water would quickly weaken immunity, thus allowing a massive new hatching of worms. In addition, adult parasites, specific to one site, would wiggle their way through the fresh barotraumatic tears in the sinus membranes into delicate areas normally protected from these critters.
Dr. Morimitsu (2) examined a number of ears from three different toothed-whale mass strandings in Japan and found the acoustic nerve degenerated by parasitic invasion in all specimens. He attributed the cause of these strandings this acoustic nerve damage, and thought this type of parasitic infestation to be a common occurrence in stranded marine mammals. He stated: "We believe that the resulting echolocation dysfunction is a major cause of mass stranding in these animals." It is interesting to note that he also noticed that the ear drum was also damaged and swollen..."
Morimitsu also stated that many parasites were found "embedded" in the complicated recesses of the middle ear cavity.
It's not hard to understand why Dr. Morimitsu, and other theorists attribute mass strandings to parasites; but, as mentioned below, parasites have lived in and on the bodies of whales for millions of years. These parasites have a complex symbiotic relationship with their host that relies on the health of both. They could not, and would not brandish a mob offensive that resulted in the death of an entire pod of whales at the same time. Parasites could kill a single animal, and the scientists that support the parasite theory suggest that the pod is following such an afflicted leader. However, strandings in which members of the same pod are spread over many miles of shoreline nullify this idea. Observers wonder where the leader is when they see small cluster of five or six animals scattered along twenty miles of beach. The follow the leader theory is also discredited by the medical evidence that shows that the distressed condition is not just afflicting a few members—all the whales are sick and dying.
Pressure waves from seaquakes and meteorite impacts would spread barotrauma throughout the pod and upset the parasite/host relationship of all the members. Consequently, the stranded pod would present in the parasitic condition now observed, and acoustic nerve damage would be expected, as would other parasitic infections throughout the whale's anatomy.
On the other hand, the whale experts at Sea World in Orlando felt that large numbers of worms found in the ear cavities and sinuses of stranded whales was not a problem because worms were commonly found in stranded whales. However, Dailey and Walker, studying dolphins taken in tuna nets, found twenty-nine animals out of thirty-one completely free of parasitic worms in these sinuses. Two "light" worm infections out of thirty-one healthy controls can not be considered "commonly infected.” As a matter of fact, one might suggest that the two infected animals might have received prior injury due to close contact with seal bombs used often in 1978 to frighten dolphins from tuna nets. One might also wonder what the affect of "large numbers" of parasites in the air spaces referred to by Walsh at Sea World might have on a deep diving animal's ability to equalize pressure in this part of their anatomy?
Sea World scientists like Walsh are wrong to suggest a heavy parasitic burden is normal. Sea World makes a lot of money from attending strandings and pretending to try to save the whales. They also get a tremendous amount of free TV publicity from the stranded whales. Naturally, they do not want a solution to the stranding mystery since it would likely result in the loss of millions in free publicity.
THE TRUTH ABOUT MASS STRANDED WHALES AND PARASITIC WORMS
During the millions of years that animals and plants have evolved, parasites have invaded practically every kind of living body. These bodies are called host by parasitologists, who have established Rules of Affinity to generalize about parasite/host associations. A loose version of one of the rules asserts that the ancestors of present-day parasites were themselves parasites of the ancestors of present day hosts.
In this evolutionary two-step, marine mammals and their parasitic worms have evolved for 50 million years to the point that many parasitic worms are not only unique to one species, but unique to a single location within the anatomy of the species. These parasites have specialized organs of attachment and reproduction and have lost the capacity for free living. They are totally dependent on their host for survival. Their loss is compensated by various gains, such as: food, shelter, longer life span, and protected life cycles.
The marine mammal has also lost some freedom; it must share its body and food with the parasites.
However, the presents of one species within a certain part of an animal's anatomy can and probably does interfere with the invasion of another, perhaps more injurious, species. In addition, the host may benefit from the exchange of chemical substances with the parasite.
Parasitologists have made only a beginning in their understanding of the behavior of parasites in response to immune reactions in the whale. The dilemma has bound together the fields of parasitology and immunology, and represents one of the most rapidly expanding fields of research in parasitology today. These researchers are finding that the host builds certain immunity to the parasites, which allows the presents of a manageable population. A healthy relationship between marine mammals and their parasites requires a delicate balance in immunologic function whereby both whale and parasite are able to survive.
This concomitant immunity represents such a compromise in which a few parasites in the body continuously stimulates an active immunity to re-infection by the same organism, thereby avoiding superinfection of the host. In other words, the role of the immunologic response in the host/parasite relationship is to control the parasite burden rather than to cause complete elimination. By control the numbers of one parasite, the whale can prevent the infection by a new more deadly parasite.
The distribution of parasites within a healthy whale's body is constantly and delicately regulated. Their parasitic worms are often adept to only one organ, part of one organ, or to a kind of cell. This balance is easily upset, and one species of parasites may easily overrun its usual boundaries.
There is another factor in the parasite picture. Most parasites require the ability to interrupt development and enter a resting state called quiescence. Developmental arrest frequently has more than a single function. In a regulatory manner, storage of larvae in a quiescent state limits large oscillations in parasite abundance which would put both the host and parasite in danger. A second function would be that of synchronizing the life cycles of the parasite with that of the host, such as; availability of food, season changes, and pregnancy.
The interruption of quiescence in many parasite species is brought on by changes in host factors, such as: an alteration in immunity, oxygen supply, and/or dehydration.
A barotraumatically injured marine mammal, unable to dive to the depth of their normal pray, would naturally become stressed, malnourished, and dehydrated resulting quickly in a parasitic superinfection. Parasitic migration would also be expected due to malnutrition and injury placing additional strain on the animal.
Migrating parasites would be allowed access into areas not normally infected through membranes ruptured in the initial barotrauma. Therefore, the parasitic damage to the acoustic nerve observed by Morimitsu is to be expected in whales exposed to excessive pressure waves from seaquakes.
References:
Dailey, M.D., W.A. Walker (1978) Parasitism as a Factor (?) in Single Strandings of Southern California Cetaceans, J. Parasitology, 64(4) pp. 593-596
Morimitsu, T. et al (1987) Mass Stranding of Odontoceti Caused by Parasitogenic Eighth Cranial Neuropathy, J. Wildlife Diseases, 23(4) pp 586-590
Walsh, M.T. et al (1991) Medical Findings in a Mass Stranding of Pilot Whales in Florida. NOAA Technical Report NMFS 98: Marine Mammal Strandings
Walsh, M.T. et al (1991) Mass Strandings of Cetaceans, chapter 39, page 673, CRC Handbook of Marine Mammal Medicine: Health, Disease, and Rehabilitation, CRC Press, Boca Raton, Florida
Thompson, S.N. (1990) Physiological Alterations During Parasitism and Their Effects on Host Behavior in Parasitism and Host Behaviour, Barnard, C. J. & J.M. Behnke, Pub. by Taylor & Francis