Glenn H. Waddell, PhD
Although the literature is not replete with references to tumors in marine mammals, one cannot survey the reports on tumors of other marine species without suspecting that tumorigenesis does indeed occur in these animals. The failure of observing tumors in marine mammals is probably due to the lack of sufficient numbers of observations.
Tumors in animals appear to be almost as ubiquitous as the bacterium Escherichia coli is to the biochemist and microbial geneticist. This includes not only the two and four legged animals which room the land areas of the world, but also the animals that room the lakes and oceans of the world as well.
With the report of Peyton Rous in Lill (1) of a virus of chickens which caused neoplasia, the quest for other virus-host relationships terminating in the initiation of tumors began. The Rous Sarcoma virus now bears the name of its initial observer and causes a spindle -celled sarcoma in the -mesenchymal tissues of chickens and turkeys. Figure 1 depicts a chicken which had been inoculated with such a virus.
Since Rous' initial observation of virus as a cause of cancer, a great deal of information has been cained through the utilization of other viral agents and a myriad of hosts to demonstrate the oncogenic, or tumor producing, properties of assorted viruses. These viruses and their hosts are listed in Table I.
The animal tumor viruses can be separated into the following Groups as depicted in the table. First, the papovavirus groupwhich includes among others the polyoma virus and the papilloma viruses. The polyoma virus is capable of inducing as marty as 26 different types of tumors in its host (2). Another virus of this group, SV40, or the vacuolating virus, is capable of transforming human primary fibroblast cells in tissue culture (3). The papova viruses represent small viruses whose genome is composed of circular deoxyribonucleic acid (DNA), and which replicate in the nucleus of its host cell (4). Second, the adenoviruses of human origin, consisting of types 12 and 18. The adenoviruses are also DNA viruses, wall in size which also replicate in the nucleus of its hog call. Third, the Ml group, including the large DNA viruses causing fibromas and myxomas. These viruses we unique In that they am DNA viruses which replicate in the cytoplasm of their host cells. Fourth, the avian leukosis group of viruses, of which Rous Sarcoma virus (RSV) is a representative. These are enveloped virions with large ribonucleic acid (RNA) gonomes (5). Pure RSV is defective. Fifth, the mammary and kidney carcinoma group, and finally, the rather large group of leukemic viruses.
The mechanics of oncogenesis by then viruses has become one of the mom interesting areas of study in virology. Although the precise mechanism of cellular transformation is unknown; several factors have come to light in studies in this am of investigation. It has been well established that in the intact animal cellular transformation, or oncogenesis, occurs only during a short period after birth of the host. There are only vow exceptions to this general rule. This finding would tend to indicate that the Immunological mechanism and other transformation-inhibiting factors are present in older animals. Moreover, although not adequately proven, many Investigators believe that the viral genome is integrated into the papilloma viruses. The polyoma virus is capable of inducing as Marty as 26 different types of tumors in its host (2). Another virus of this group, SV40, or the vacuolating virus, is capable of transforming human primary fibroblast cells in tissue culture (3). The papova viruses represent small viruses whose genome is composed of circular deoxyribonucleic acid (DNA), and which replicate in the nucleus of its host cell (4). Second, the adenoviruses of human origin, consisting of types 12 and 18. The adenoviruses are also DNA viruses, wall in size which also replicate in the nucleus of its hog call. Third, the Ml group including the large DNA viruses causing fibromas and myxomas. These viruses we unique In that they am DNA viruses which replicate In the cytoplasm of their host cells. Fourth, the avian leukosis group of viruses, of which Rous Sarcoma virus (RSV) is a representative. These are enveloped virions with large ribonucleic acid (RNA) gonomes (5). Pure RSV Is defective. Fifth, the mammary and kidney carcinoma group, and finally, the rather large group of leukemic viruses.
Moreover, although not adequately proven, many Investigators believe that the viral genome is integrated into the host cell genome. The evidence for integration of the viral genome is largely based upon the appearance of viral antigens on the transformed call surface (6). Integration of the viral genome is suspected as being akin to lysogeny as demonstrated in bacteriophage systems (7). Further, a circularity of viral nucleic acid (DNA) has been proven for many members of the papovaviruses. Shope papilloma, polyoma, and SV40 have been established as having a circular genome (8, 9, 10). This is important, as shown in the lambda phage-E. coli lysogenic system, for the integration of the phage chromosome into the host call genome as visualized by Campbell (11).
The recent findings on the nature of Rous Sarcoma virus has demonstrated that the virus is defective. This virus, having a large RNA genome, is unable to code for its own protein coat. It requires another virus (a helper virus) to code for the capsid proteins. This is accomplished by either the Rous Inhibitory virus (RIF) or the Rous as cited virus (RAV) (12).
The next two figures (Figures 2 and 3) represent the extent of oncogenesis resulting when a member of the adenovirus group is inoculated into newborn hamsters. These tumors represent undifferentiated sarcomas, and as revealed in the figures may obtain sizes equal to or larger then that of its hosts.
Hamsters inoculated with the cell-free extracts of Adenovirus type 12. The animals were inoculated when less than 48 hours of age. These animals were approximately 3 month of age when sacrificed.
Removed tumors induced by Adenovirus type 12 from the animals depicted in Figure 2. The animals from which the tumors were removed are shown for comparison of sizes.
The need for further clarification of the mechanics of oncogenesis is obvious. It Is also obvious that viruses have been very dramatically incriminated in the causation of tumors, particularly as for as land animals are concerned. It is likewise obvious that a viral etiology may be found for many of the tumors found in marine animals. Tumors in fishes are plentiful, particularly in those species of fish commonly caught in large quantities where a large population can be observed. All tumors found in land species of animals have their counterparts in fish (Table II). Papillomas, adenomas, adenocarcinomas, and epidermoid carcinomas are a few of the different types of tumors found in the epithelia IAL tissues of fishes. Fibromas, sarcomas, myxomas, osteomas, ipomos, hemangiomas, and lymphomas ore characteristic types of tumors described in mesenchymal tissues. Melanomas and other tumors of pigmented tissues occur frequently in fishes (13).
It is clear that the types of tumors found in tumor bearing fishes have their counterparts in mammals. Although the literature is not replete with reports of tumor bearing marine mammals; the widespread observations of tumors in the lower marine vertebrates would suggest that these are present. Many species of fishes found in local marine habitats have been reported to be off I icted with tumors. The commonly known species of: snappers, angelfish, croakers, slippery dicks, moray eels, sand sharks, trout, whiting, sea bass, scorpion fish, butterfly fishes, file fishes, trigger fishes, and spade fishes are only a few which have been reported to have tumors.
Figure 4 shows a tumor of the mesenchymal tissues in the common spade fish. This fish was observed in the large reef tank at the Miami Seaquarium and submitted by them for laboratory investigation (14). The tumor measured approximately 3.5 cm in diameter and protruded about 2.5 to 3 cm from the side of the fish. Histologically, the tumor was a lipoma.
A tumor of the mesenchymal tissues of the spadefish. The tumor was histologically a lipoma measuring approximately 3.5 cm in diameter.
In August of 1963, while visiting the Florida Keys, an approximately 3 to 5 year old green turtle of the species Chelonia mydas was captured. This turtle is shown in figure 5. It was evident upon capture that the animal had extensive tumors covering nearly all of the soft tissues on its ventral surface. These tumors ranged in color from white, to black, to red. Figure 6 shows a close up view of the tumors on the ventral surface near the hind flippers. Histologically, these tumors were fibro-epithelial papillomas. Figure 7 shows the extent of affliction in this animal, for tumors were even exhibited on the eye-coverings. Because of the extent of affliction, the animal became blind shortly after capture, and being unable to see his food died in about one month.
An approximately 3-year old green turtle captured in the Florida Keys showing extensive papilomas covering the soft tissues on the ventral surface.
A close-up view of the ventral surface near the hind flippers of the turtle shown in Figure5. This view shows the extent of coverage by these growths. The Tumors ranged in pigmentation from red to white to black.
Tissues from these tumors were minced, and minced tissues as well as coli-free extracts were inoculated into separate groups of young green turtles otariid through the cooperation of the Office of Naval Research (15). The lack of adequate holding facilities at this time however, did not permit conclusive results to be obtained from any of the inoculations.
Nearly one year later, however, another turtle of the some species was captured in Biscayne Bay off Miami, Florida. This turtle exhibited similar tumors on its ventral surface of the front flippers. The age of this animal was approximately one-year. No tumors were observed in any other part of this turtle; and since this was the site of our inoculation, it could possibly represent an animal which we had inoculated. There Is no way of proving this conjecture of course, but although we attempted to mark the inoculated animals, some may have been released Into Biscayne Bay along with a large number of normal green turtles of the same age when the Miami Seaquarium released their animals. Both the Inoculated groups as well as the normal turtles were hold in the same holding pen.
|Figure 7. |
A dorsal view of the head of the animal depicted in Figure 5. Note the neoplasia on the eye coverings of this turtle which eventually led to his death.
The next view (Figure 8) shows the characteristic papillae as exhibited by these tumors. It is interesting to speculate that these tumors have a viral etiology, for papillomas in rabbits, cattle, man and freshwater fishes have been shown to be caused by virus. Of further interest, personal communication with commercial fishermen and men with the commercial turtle industry in the Florida Keys indicate that approximately 95 per cent of the turtles captured in Florida Bay are afflicted with papillomas; while only approximately 5 per cent of those captured from the Atlantic Ocean side show this affliction. This is somewhat borne out by references to similarly off listed animals captured off Ceder Key in the Gulf of Mexico (16). Moreover, the commonly called loggerhead and the hawksbill turtles are similarly afflicted. Research on the tumors found in fishes and turtles provide great promise for the study of virus-host interactions leading to tumorigenesis, as well as the immunological mechanisms involved. A return to these studies is contemplated in the very near future.
A view of the second turtle found with papillomas showing the characteristic papillae exhibited by these tumors.
There has recently been increased interest in tumors of lower animals including the marine fishes. This interest has been such that the Smithsonian Institution in conjunction with the National Cancer Institute has established a registry of tumors in lower animals in order to collect specimens which will aid in the fundamental understanding of neoplastic processes. This registry is now housed in the U.S. National museum in Washington, D.C. and contains many documented specimens of tumors found in the marine animals (17).
So the search for tumors and their causes goes on. Perhaps with the interest in marine mammals exhibited at this symposium, there will be increasing reports of tumors in the mammals inhabiting the ocean environment.
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Submitted to the Author by the Director of Laboratories at the Miami Seaquarium, Miami, Florida.
Newborn green turtles supplied by the Office of Naval Research during research under contract No. NONR-3310 (00) at Variety Childrens Research Foundation, Miami, Fla.
Lucke, B. (1938) Studies on Tumors in Cold-Blooded Vertebrates. Ann. Rept. Tortugas Lob., 1937/1938, 92.
Registry of Tumors in Lower Animals, Smithsonian Institution, United States National Museum, Washington, D.C.