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White spot disease caused by white spot syndrome virus (WSSV) is responsible for harming shrimp aquaculture industry and results in a pandemic throughout the world. Undeniably, the knowledge on geographic distribution, transmission, virulence, and seasonal prevalence of this disease alongside information on the distribution of disease-resistant shrimps may be helpful to understand important aspects of disease biology. This study was intended to estimate WSSV prevalence by qualitative and quantitative PCR method among the Penaeus monodon samples collected from four different places namely Digha, West Bengal; Chilika, Orissa; Visakhapatnam, Andhra Pradesh; and Chennai, Tamil Nadu at three different seasons in the period of 2011-2013 from east coast of India. Along with this, the disease-resistant prevalence was also investigated using earlier developed 71 bp microsatellite and 457 bp RAPD-SCAR DNA marker among the collected shrimps. Qualitative PCR depicted that the cumulative WSSV prevalence at four places was the lowest (0%) at pre-monsoon, whereas, it was the highest (21.2%) during post-monsoon season. Quantitative real-time PCR showed the average copy number of WSSV to be the highest (~10(3) copy μg(-1) shrimp genomic DNA) at post-monsoon season. Additionally, estimated disease-resistant prevalence was the highest in Visakhapatnam (79%) and lowest in Digha (21%). It is well known to all that a trait cannot be identified using a single genetic pattern. This study will significantly contribute insight to develop specific pathogen-resistant (SPR) seeds of P. monodon simultaneously using two DNA markers that would be a cost-effective and safer approach towards disease prevention instead of conventional trends of seed generation from unselected wild broodstock.

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White spot disease (WSD) which is caused by white spot syndrome virus (WSSV) creates severe epizootics in captured and cultured black tiger shrimp, resulting a huge loss in the economic output of the aquaculture industry worldwide. Performing selective breeding using DNA markers would prove to be a potential cost effective strategy for long term disease control in shrimps. In the present investigation, microsatellite DNA fingerprints were compared between naturally occurring WSSV resistant and susceptible populations of Penaeus monodon. After PCR with a set of shrimp specific primers three reproducible DNA fragments of varying sizes were found, among which 442 bp and 236 bp fragments were present in considerably higher frequencies in the WSSV susceptible shrimp population (p ≤ 0.0001). After WSSV challenge experiment the copy no. of WSSV was determined using real-time PCR, where it was found to be almost 4 × 103 fold higher in WSSV susceptible shrimps than in the resistant ones. Thus, these microsatellite DNA markers will be useful to distinguish between WSSV susceptible and resistant brood stocks of P. monodon. Sequencing studies revealed that these DNA markers were novel in P. monodon. Highest WSSV resistance using these DNA markers, was observed in the shrimp populations of Andaman Island and Chennai among the different coastal areas of India, suggesting these places as safe for specific pathogen resistant brood stock shrimp collection. This study will be a very effective platform towards understanding the molecular pathogenesis of WSD for generation of disease free shrimp aquaculture industry.

The rapidly developing nature of many pathogens creates a severe threat to biodiversity. Highly contagious diseases often cause severe epizootics to the natural population and leading to the loss of ecological balance. Expeditious disseminating nature of infectious pathogens helps to understand the disease prevalence in a specific biogeographical region. White spot syndrome virus (WSSV) is the most lethal, contagious, waterborne virus and responsible for the white spot disease (WSD) in penaeid shrimps. White spot disease resistance, a quantitative phenomenon and controlled by many genetic and ecological elements. Variation of quantitative WSSV prevalence is dependent on many environmental factors namely salinity, temperature, pH (Gao, Kong, Li, Xiao, & Meng, 2011), and storms, rain, seasonal variation of tidal currents and fluctuation of seawater (Iqbal, Kabir, Alan, Mamun, & Hossain, 2011). Previously, Mandal et al. (2012) reported that oceanic current patterns might have an effect on population structure. WSSV-susceptibility or WSSVresistance is controlled by climatic conditions and depends on the physical parameters as well as the surroundings' environment of water (Mondal, Dutta, Chakrabarty, Mallik, & Mandal, 2019). In this article, we represented an ecological perspective of the disease-resistance prevalence phenomenon in Penaeus monodon.