Macroscopic evidence, histological sections, transmission electron microscopy (TEM) evaluation, and PCR analyses of 25 apparently diseased juvenile spiny lobsters Panulirus argus from the reef lagoon of Puerto Morelos, Mexico, showed the presence of Panulirus argus Virus 1 (PaV1). Cowdry Type A intranuclear viral inclusions were observed in histological analyses, icosahedral viral particles were observed by TEM, and PCR using specific primers for PaV1 amplified a fragment of 499 bp. This is the first report of PaV1 infecting P. argus outside the Florida Keys, USA. KEY WORDS: Spiny lobster · Panulirus argus · PaV1 · Cowdry Type A intranuclear inclusionsResale or republication not permitted without written consent of the publisher Dis Aquat Org 79: 153-156, 2008 water) and processed by a routine histological method followed by hematoxylin and eosin (H&E) stains (Lightner 1996). Stained sections were observed under a standard light microscope to examine histopathological changes and the images were captured using a digital camera (Evolution™ LC Color). The severity of infection of each tissue type was estimated using the numerical scale of Bell & Lightner (1987), who assigned infection severity grades from 0 to 4 based on the estimated number of diagnostic Cowdry Type A intranuclear inclusions (CAI) per microscopic field(s) at 40 X: Grade 0 = no CAI observed; Grade 1 = 1-5 CAI/200 fields; Grade 2 = 1-2 CAI/20 fields; Grade 3 = 1-5 CAI/2 fields); and Grade 4 >10 CAI/field.For the TEM examinations, the hepatopancreas of 8 lobsters were first fixed in 2.5% glutaraldehyde with 0.2 M sodium cacodylate buffer, then in 1% osmium tetraoxide and further dehydrated in increased serial dilutions of ethanol. Finally, samples were mounted in Spurr's resin. Ultra-thin sectioned samples placed on grids were processed through a routine lead citrate stain and observed with a Jeol microscope (JEM-1200 EX II) (Reynolds 1963).Fifteen lobsters were used for the PCR analysis. Genomic DNA were extracted from ~25 mg of hepatopancreatic tissue using the wizard ® genomic DNA purification kit (Promega ® ) according to the manufacturer's protocol. The primers specific for PaV1 45aF-TCCAGCCCAGGTACGTATC and 543aR-AACAGA-TT-TTCCAGCAGCGT that amplify a region of 499 bp were used after a modification of the original protocol of Montgomery-Fullerton et al. (2007). All PCR reactions were carried out in a total volume of 25 µl containing ~32.5 ng of DNA, 0.33 µM of each primer, 2.5 mM of MgCl 2 , 1.2× reaction buffer (50 mM KCl, 10 mM Tris-HCl, pH 9.0, 0.1% Triton X-100), 0.4 mM dNTPs mixture (Promega ® ), and 2.5 U of Taq DNA polymerase (Promega ® ). Reactions were run on a thermal cycler (TECHNE TC-312) at 94°C for 10 min, followed by 30 cycles of 94°C for 30 s, 63°C for 30 s, and 72°C for 1 min, with a final extension of 72°C for 10 min. PCR products were electrophoresed on 2% agarose gels and bands were visualized using 0.1% ethidium bromide stain on a UV transilluminator. DNA from lobsters collected in the Reef lagoon of Puerto More...