Isolation of Aeromonas hydrophila During an Outbreak of Hatchling Alligator Syndrome (HAS)
IAAAM 1988
Paul T. Cardeilhac1, DVM, PhD; D.K. Peters
1University of Florida, Gainesville, FL


Hatchling alligators (Alligator mississippiensis) from a group concentrated in holding pens prior to statewide distribution were reported weak and dying. Five moribund hatchlings were presented to the Department of Special Clinical Sciences for evaluation. Hematology, microbiology, gross and microscopic pathology samples were collected. Water samples from the well and the pond located at the site of hatch and early rearing were obtained for microbiology. Aeromonas hydrophila an organism frequently involved in the stress-related Hatchling Alligator Syndrome (HAS), was cultured from the blood and tissues and its susceptibility to antibiotics determined. Development of husbandry techniques and treatment regimens aimed at prevention and control of such outbreaks is an ongoing project in our lab.


Intensive culture of the American alligator (Alligator mississippiensis) is being developed as a production aquaculture industry with meat and hides as the end product for potential world markets(1). Prevention and control of disease outbreaks in alligators under intensive culture has been challenging since there is no antibiotic approved for general use in these animals at this time. A complex of bacterial infections caused by opportunistic organisms which are of low virulence and usually noninvasive to the host has been a serious disease problem for alligator production(1,2,3). This complex of bacterial diseases has been termed Hatchling Alligator Syndrome (HAS). Aeromonas hydrophila is a Gram negative rod-shaped bacteria which usually is motile and often can be demonstrated in waters considered both clean and polluted(4,5). The American alligator has previously been reported to develop disease including septicemia from which Aeromonas hydrophila has been isolated(1,6,7,8,9). The prevalence of Aeromonas isolates has been reported to be as high as 40.5% (9). This report deals with an outbreak of HAS from which multiple bacterial organisms including Aeromonas hydrophila were isolated.

Case History

Hatchling alligators concentrated in holding pens for a few weeks after hatch were reported weak and dying. These young alligators were part of a group of 4563 hatched from 9366 eggs collected from several Florida lakes. The alligators were placed into indoor tanks supplied with flowing water from a nearby pond. Five moribund hatchlings were presented to the Department of Special Clinical Sciences for evaluation. A total of 279 (6.1%) were reported dead by 90 days following hatch (F.F. Percival, University of Florida, personal communication).

Clinical data from these hatchlings leading to an understanding of the problem was important since these animals were part of a cooperative research study from which surviving hatchlings were to be distributed to members of the alligator farming industry located throughout the state. Many alligators hatched and housed with those presented were being transported to private farms, some with large existing populations of alligators at various stages of growth.

Hematology, gross and microscopic pathology, and microbiology samples were obtained and submitted for evaluation. Cultures were also submitted on water samples from both the pond and a well at the site.

Results and Discussion

Clinically the animals were presented as moribund. They were not emaciated, showing body condition considered normal for young hatchlings. Food intake was not a factor because these alligators were not yet being fed and still were completing the utilization of yolk.

Changes from expected normal values were observed in white blood cell (WBC) counts, protein, SGOT, and glucose (10). WBC counts were below normal in three of the five animals with one as low as 400 (normal 4,700-9,000/microliter). Serum total protein values were uniformly elevated with one individual at 11.9 (normal 3-5 g/dl). One of the hatchling alligators had an elevated SGOT at 420 (normal 156-285 IU/L). Two of the five animals had blood glucose levels above normal, the highest being 476 (normal 50-200 mg/dl).

Gross pathology indicated necrotic$ ulcerated skin lesions on the flanks of two hatchlings, as well as one purulent eye lesion, one ulcerative pharyngeal lesion, and pale livers on all animals.

Multiple histological changes were observed in the tissues examined. Fatty infiltration of the liver was detected and would be expected in these young animals that were not eating. Marked melanin pigment was evident in the liver sections, however, this is often observed in reptilian livers (10). The lung had areas of congested mucosa and some edema fluid in alveoli. Inflammation was evidenced by the presence of heterophils and perivascular lymphocytes in tissue sections. Bacteria and fungal elements were both demonstrated histologically with the use of special stains.

Microbiology indicated the presence of multiple organisms in the tissues of these hatchlings. Blood cultures have been used in previous work with hatchlings to assess bacterial diseases (1,2). Aeromonas hydrophila was the primary organism found in the blood and other tissues of the alligators under investigation. Aeromonas was found in blood, kidney, liver, lung, eye, tongue, and water from both the pond and well. The concentration of Aeromonas in pond water was ten times that of well water.

Pseudomonas aeruginosa and the Gram positive organisms Staphylococcus and Streptococcus were also found in the tissues of some of these alligator hatchlings.

Antibiotic susceptibility tests on the Aeromonas and Pseudomonas isolates demonstrated multiple resistance to antibiotics. Aeromonas was resistant to fourteen of the twenty two antibiotics in the test group and Pseudomonas demonstrated resistance to eighteen of the twenty two.

Stress is an important factor in allowing opportunistic bacteria which are normally present in the aquatic environment to become pathogens. Husbandry practices which reduce temperature and handling stress and dietary supplementation of critical nutrients may be used to reduce the negative effects of these invaders (1).

Hatchling alligators from the present study were transferred to farms with good husbandry practices and placed on diets supplemented with critical nutrients, high biological value proteins and antibiotics. Under these conditions losses were limited with most becoming viable hatchlings.


1.  Cardeilhac, P.T. and D.K. Peters. 1988. Management problems of alligator production. J. Vet. and Human Tox. (In Press).

2.  Cardeilhac, P.T., B.R. Collins, F. Ruisi, S. Sundloff, R. Larsen and T. Lane. 1986. Preliminary studies on the use of oxytetracycline to control hatchling alligator syndrome (HAS). Proc. Int. Assoc. Aquatic An. Med. 1(3): 21-27.

3.  Cardeilhac, P.T. and D.K. Peters. 1987. Estimation of an effective oral dose of virginiamycin to control hatchling alligator syndrome (HAS). 18th Proc. Int. Assoc. Aquatic An. Med. (In Press).

4.  Carter, G.R. 1986. Essentials of Veterinary Bacteriology and Mycology. 3rd Edition, Lea and Febiger, Philadelphia, Pennsylvania, 261 pp.

5.  Shotts, E.B. 1984. Aeromonas. In Diseases of Amphibians and Reptiles. G.L. Hoff, F.L. Frye and E.R. Jacobson (eds.). Plenum Press, New York, 784pp.

6.  Novak, S.S. and R.A. Seigel. 1986. Gram-negative septicemia in American alligators (Alligator mississippiensis). J. Wildl. Dis. 22: 484-487.

7.  Goren, R.W., T.C. Hazen G.W. Esch and C.B. Fliermans. 1979. Isolation of Aeromonas hydrophila from the American alligator, Alligator mississippiensis. J. Wildl. Dis. 15: 239-243.

8.  Shotts, E.B., J.L. Gaines, L. Martin and A.K. Prestwood. 1972. Aeromonas-induced deaths among fish and reptiles in an eutrophic inland lake. J. Am. Vet. Med. Assoc. 161:603-607.

9.  Shotts, E.B. 1983. Bacterial diseases of alligators: an overview. Proc. 1st Alligator Production Conference, University of Florida pp 36-41.

10. Marcus, L.C. 1981. Veterinary Biology and Medicine of Captive Amphibians and Reptiles. Lea and Febiger, Philadelphia, Pennsylvania, 239 pp.

Speaker Information
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D. K. Peters

Paul T. Cardeilhac, DVM, PhD
University of Florida, College of Veterinary Medicine
Gainesville, FL

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