Daggerblade grass shrimp (Palaemonetes pugio): A reservoir host for yellow-head virus (YHV)

Yellow-head virus (YHV) is a major pathogen in penaeid shrimps. We surveyed 13 crustacean species in eight families from two orders that are commonly found in the Mississippi coastal area and freshwater environments as potential reservoir or carrier hosts of YHV. Using semi-nested polymerase chain reaction (PCR) on relatively small sample sizes, we did not detect any natural infection. However, when the daggerblade grass shrimp, Palaemonetes pugio, and the blue crab, Callinectes sapidus, were exposed to YHV by injection and per os, YHV was detected in the tissue of P. pugio and in the hemolymph of C. sapidus when tested by semi-nested reverse transcription PCR (RT-PCR) and real time quantitative reverse transcription PCR (qRT-PCR). YHV replicated in P. pugio, causing 8% mortality (9/112) after injection, with the viral titer reaching a peak at 14days post-inoculation (dpi) and remaining detectable at 36dpi. The number of infected animals and viral load, however, were relatively low but the virus still remained infectious to penaeids when administered by feeding. When YHV was injected into P. pugio, in situ hybridization detected a positive response to it at 7dpi in connective tissue of hepatopancreas, muscle, and midgut. Viral RNA in injected C. sapidus remained at a low level for 3days, and it was not detected from 7dpi onwards. In fed C. sapidus, the viral RNA reached a peak at 3dpi and still detectable at 7dpi, but it became undetectable at 14 and 21dpi. These data suggest that P. pugio under some conditions could act as a reservoir host for YHV but that the blue crab could serve as a poor, short term carrier host only.