Abstract

In reptiles, paramyxoviruses (PMV) have been found predominately in snakes, where they are associated with respiratory disease and, in some cases, neurologic disorders.^1,3,5,6,8-11 PMVs have also been found in lizards,² but their significance in these animals is unclear. One study demonstrated antibodies against PMV in free-living iguanas in Central America.⁷ Studies on PMVs isolated from snakes and comparisons with PMVs from other animals have shown that these viruses are endogenous reptile viruses.^2-4,12

In this study, pharyngeal and cloacal swabs were collected from a total of 30 lizards: 13 Xenosaurus grandis, 12 X. platyceps, and 5 Abronia graminea. Plasma was obtained from 23 of the animals. All samples were collected in June and July of 1999. All lizards were wild-caught between May and August of 1998. X. grandis and A. graminea were caught in Vera Cruz, Mexico and X. platyceps in Tamaulipas, Mexico. Animals had contact with one another following capture, but were not exposed to other reptiles. The lizards were being used in behavioral studies at the University of Puget Sound, Tacoma, Washington. All of the animals tested were clinically healthy at the time of sampling.

Pharyngeal and cloacal swabs were placed in cell culture medium and inoculated onto Terrapene heart cells (TH-1, ATCC, Rockville, MD) and chicken embryo fibroblasts (CEF¹³) for virus isolation. Cell cultures were incubated at 28 °C for at least 14 days and observed daily for cytopathic effects (CPE). Cultures showing signs of CPE were harvested and passaged onto the same cell line for further investigation. Plasma was tested for antibodies against a PMV isolated from one of the tested animals and a PMV isolated from a Varanus prasinus (isolate No. 3319/95⁷) by a hemagglutination inhibition test (HI).¹⁴ A titer > 16 was considered significant. Serum from specific pathogen free (SPF) chicken was used as a negative control. Chicken antiserum against an avian PMV-1 was used as a positive control.

A cytopathogenic agent that caused syncytium formation in both TH-1 and CEF was isolated from the cloacal swab of one of the X. platyceps. The isolate was given the name 28xpc/99. The isolate could be passaged in cell culture, and was sensitive to chloroform indicating that it could be an enveloped virus. Growth of the isolate in cell culture was not influenced by addition of 5-iodo-2'desoxyuridin (IUDR), which inhibits the DNA-polymerase, to the cell culture medium, indicating that it could be an RNA virus. The virus isolate was able to agglutinate chicken erythrocytes at room temperature. Examination of infected cell culture supernatant showed polymorphous enveloped particles consistent with PMV.

The results of the serologic tests are presented in Table 1. Using 28xpc/99, HI's were carried out with plasma from 23 animals. 4 of these animals had detectable antibodies. Plasma from 22 animals was tested for antibodies against a different reptilian PMV, 3319/95. Seven of the animals had detectable antibody titers against this virus. Only one X. grandis and an A. graminea had measurable antibodies against both PMVs. All positive animals had antibody titers of 32 or higher.

These results show that the lizard species examined can be infected with PMVs. It seems likely that the infections originated in the wild, since the animals are believed to have had no contact with other reptiles in captivity. Gravendyck et al.,⁷ showed that free-living iguanas from Honduran islands also had antibodies against the reptilian PMV 3319/95, confirming that PMV infections exist among wild lizard populations in central America. The antibody titers measured in the iguana study were lower than those found in this study, and no virus was isolated from the Honduran animals. The clinical significance of PMVs for these animals is unclear. All of the animals tested were clinically healthy at the time of testing and remained so for the months following sample collection. Further studies are necessary to compare the PMV isolated from one of the animals tested with PMVs from other reptiles.

Table 1. Results of a serosurvey for paramyxoviruses in wild-caught Xenosaurus grandis, Xensaurus platyceps, and Abronia graminea.

a. HI = hemagglutination inhibition test.
b. Number positive (titer 16 and higher)/total tested (percent positive).

Acknowledgments

The authors thank Dr. Edward A. DeGrauw University of Pudget Sound, Biology Department., Tacoma, WA for his expertise and the use of the animals and Dr. Werner Herbst, Institut für Hygiene und Infektionskrankheiten der Tiere, Justus Liebig University Giessen, Germany, for electron microscopy.

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