Abstract

In this study, the serum of a mature male Tursiops aduncus was screened for the presence of antibodies to certain viruses and to Mycoplasma pneumoniae. Clinical symptoms of respiratory discomfort were followed by a convalescent rise in serum viral antibody titres for Parainfluenza II and 111, the Respiratory Syncytial Virus, Cytomegalovirus, and also for Mycoplasma pneumoniae. A synopsis of the major features of these diseases are discussed in brief.

An anthropozoonosis became apparent during concurrent studies on increases in human titres in a local metropolitan community, indicating possible transmission of viral respiratory diseases by trainers during handling.

Introduction

Respiratory diseases are common amongst the captive dolphins held at the Durban Dolphinarium and, together with gastro- in test trial problems, form the majority of those cases requiring medical intervention. The incidence of respiratory problems tended to have a seasonal occurence and, once established in an animal, would rapidly spread from dolphin to dolphin in a relatively short time, indicating a disease of an infectious, contagious nature.

In order to establish the aetiological agent involved, blood was collected from the central veins in the flukes and analyzed by means of the complement fixation test to determine serum antibody titres to selected viruses and to Mycoplasma pneumoniae. Bacteriology of the expired air proved to be inconsistent, despite a leucocytusis in the majority of the respiratory cases.

Although the sera of three species of captive dolphin were analyzed over a period of several years, this particular study is confined to a mature male Tursiops aduncus which had been in captivity for four years prior to the commencement of the analysis. This anima was also more prone to respiratory problems than any of the other captive dolphins.

Routine monthly blood samples were analyzed to establish baseline data and further samples were collected during periods of illness. In the course of the study, trends in the elevation of antibody titres to certain microorganisms became apparent and could he linked to clinical episodes of respiratory illness. An attempt is made to describe some of these episodes which could be correlated to infection by specific organisms.

Materials, Methods and Results

Mycoplasma Pneuoniae Pneumonis

Clinical Features

These are summarized as follows: lethargy; partial intermittent anorexia; a frequent explosive, often paroxysmal cough; labored respiratory effort; tenacious, clear, white frothy mucus around the blowhole; mucoid faeces; elevation in rectal temperature and a nebulous keratitis.

If untreated, the illness persisted for weeks; but if specific therapy was applied, symptoms rapidly disappeared within a few days.

Clinical Pathology

In all cases, a leucocytosis with an accompanying neutrophilia was evident. The serum globulin fraction increased and a decrease in serum alkaline phosphatase was recorded. A heavy bacterial growth was cultured from the expired air taken above the blowhole, but the organisms cultured were those found on routine monthly plates and were therefore regarded as commensals.

Once the mycoplasma organism was identified as the aetiological agent based an a four-fold serum antibody titre increase, expired air "cough" plates, comprised of differential agar, A 2 ) for mycoplasma, were used to culture the pathogen. The plates were incubated anaerobically at 35C for a 48 hour incubation period. "Fried-egg" colonies, typical of Mycoplasma spp., ere indentified under low power (x inn) using a direct transmitted light through the substage condenser.

Treatment

Tylosin (Tylan 200, Elanco) was selected as the drug of choice due to its particular efficacy against the organism which is frequently encountered in the pig industry. A dosage of 32 mg/kg body mass was given intramuscul arty once daily. The response to treatment was rapid with complete remission of symptoms within six days, whereupon treatment was discontinued. the high dosage level was selected as preliminary trials with other drugs indicated that higher dosages (normally three-fold that of terrestrial mammalian dosages) are required in dolphins.

However, at this high dosage, the large volume injected tends to procure a myositis and for this reason, the oral tablet form was selected for use at a high dosage of 50 mg/kg body mass t.i.d. The tablet form was well tolerated; the only side effect noticed being a mild diarrhea with mucoid feces.

Disease Discussion

M. pneumoniae in dolphins appears to cause symptoms commonly observed in other animals and in man, i.e. pneumonia with a general debilitation. If left untreated, the course of the disease is chronic. If diagnosed and specific therapy is applied, recovery is prompt, as antibody levels revert to baseline levels within a few weeks. Of interest is the fact that outbreaks of M. pneumoniae in the dolphin coincided with epidemiological outbreaks in man, including the trainers. It is therefore highly probable that an anthropozoonosis exists; the organism also being capable of infecting the other dolphins in close proximity.

Cytomegalovirus

Clinical Features

These are summarized as follows: selective partial anorexia; inat tent iveness; orange-brown coloured faeces which tended to float on the water surface; small circular depressed black spots in the dermis, particularly on the dorsum of the thorax near the vicinity of the blowhole; slightly labored respiration with an audible wheeze on exhalation

Clinical Pathology

A leucocytosis with a marked neutrophilia was recorded. An increase in serum alkaline phosphatase was recorded, indicating a possible hepatitis which has been observed in other animals and man infected with CMV. An increase in serum globulins was also recorded.

No significant bacterial changes were isolated an the expired air "cough" plates.

No attempt has, as of yet, been made to isolate the virus from tissue specimens. A five-fold increase in serum antibody titre occurred, which rose rapidly within a few days and remained elevated for approximately two months.

Treatment

Symptomatic, aimed primarily at preventing secondary bacterial infection.

Disease Discussion

The CMV, like others in the Herpesvirus group, exhibit a tendency to latency or persistence in the host. They are ubiquitous agents affecting many body systems. During active periods, the virus may be present in all body fluids, and it has been reported that, in humans, infection routes in the genital tract were parallelled by increased sexual activity (1). Excessive mating was observed in the dolphin prior to illness.

Although normally considered an opportunistic pathogen producing serious debilitating disease only in the immunocompromised host, fluctuations in humeral antibody titres are found in individuals with persistent infections. This may be due to contact with a heteroloqous strain of the virus or to activation of a homologous strain. In any event, the peak antibody titres are already found in the acute phase sera. It has been Suggested that cumulative insults of focal viral cytopathology are occurring and may eventually lead to immunucomplex disease (2).

In the dolphin it would appear that this virus presents primarily as a pneumonia complex, but is also capable of affecting other system, in particular the liver.

Parainfluenza II and III

Clinical Findings

These are summarized as follows: inappetence; grey to brown coloured faeces having a lumpy dense consistency; wheezing on inspiration. This viral disease appeared clinically less debilitating than those previously discussed, and the animal continued to mate on frequent occasions throughout the period of illness.

Clinical Pathology

A mild leucocytosis was recorded. No abnormalities were observed in either the biochemistry or in serum electrophoresis. Bacteriology yielded a heavy growth of Pseudomonas aeruginosa and Vibrio alginolyticus from the "cough" plates. The serum viral antibody titre to Parainfluenza III was slow to rise to a level of diagnostic significance. During one incidence, a simultaneous rise in the Mumps-V antibody titre was recorded. Whether this was in response to exposure to the mumps virus or due to a cross reaction is not known as this stage. However, heterologous antibody responses between the various Parainfluenza viruses and the mumps virus are known to occur.

Treatment

Symptomatic, in order to prevent secondary bacterial infection. As the symptoms closely resemble those caused by M. pneumaniae, tylosin is normally selected for initial therapy.

Disease Discussion

This viral pneumonia is characterized by a slow antibody response resulting in a long illness stretching over a period of a few months. Fortunately, this respiratory disease does not appear to be particularly debilitating. The delayed clinical response to the oral administration of tylosin could have been used to eliminate M. pneumoniae as a differential diagnosis

Discussion

In the study on respiratory disease in a captive dolphin using serological complement fixation and microbiology, it became apparent that the initial insult to the respiratory Mucosa Was caused by a virus or Mycoplasma spp., with commensal opportunistic bacteria proliferating in the areas of damaged tissue, often aggravating the initial insult.

Based on preliminary trials, it would appear that tylosin is rapidly effective in destroying M. pneumoniae in dolphins. As this organism has ')Pen singularly responsible for more cases of pneumonia in our dolphins than any other organism, and as determination of the aptiological agent requires a significant increase in the serum antibody titres (seldom seen before two weeks post infection), animals exhibiting respiratory disorders are placed initially on tylosin and remain on such unless the complement fixation test or bacteriology indicate some other aetiological agent. Fortunately, tylosin is a relatively broad spectrum macrolide antibiotic, thereby effectively reducing the risk of secondary bacterial infection from opportunistic bacteria susceptible to the drug. The response to the drug or lack of it may also be used as an aid to the differential diagnosis of the aetiological agent responsible.

Of significance, and as a further aid to establishing the causative agent, it is important to be aware of the epidemiological analysis of agents responsible for respiratory disease in the existing metropolitan human population, as a titre increase to certain viruses in the human corresponded to an increase in the dolphin (3).

References

1. Davis, L.E.; Stewart, J.A.; and Garvin, S. Cytomegalovirus infection: Sereoepidermliological comparison of nuns and women from a venereal disease clinic. Am. J. of Epidem. 102(4): 327-330 (1975).
2. Welter, T.H. Clinical spectrum of cytomegalovirus infection. In: The Human Herpes Viruses: An Interdisciplinary Perspective, J. Andre & A.J. Nanamias, Eds. Elsevier, Amsterdam, 1981.
3. Windsor, I.M. and Thurman, G.D. Elevation in serum viral antibody titres in captive dolphins following respiratory disorders caused by viruses and Mycoplasma pneumoniae. Investigational Report. Oceanographic Research Institute (in press).