Crucial knowledge gaps remain in the understanding of white spot disease (WSD) transmission dynamics . To accurately characterize these dynamics, it is necessary to first understand the time course of WSD in an individual host (Jewell et al. 2016). The n, the epidemic pattern of spread can be characterized . Studying th is pattern can potentially reveal the primary transmission dynamics , aid in the determination of the point at which host-to-host transmission occurs (Giesecke et al. 2017), and which risk factors are at play (Jewell et al. 2016). The aim of this study was to analyse the horizontal transmission dynamics of WSD in L. vannamei , and to evaluate the role of some environmental components that might be involved.
First, we performed a peroral inoculation with WSSV-infected tissue inoculum (Thai-1 strain) (Thuong et al., 2016) in individually housed shrimp to characterize WSD progression. Second, we developed a peroral group infection model. Third, this model was used to identify the characteristics of an WSSV epidemic . Finally, we investigated the role of molts, feces, and water from infected populations in WSSV transmission by exposing naïve shrimp.
The WSSV Thai-1 strain had an incubation period of 24–54 hpi, and an irreversible disease progression leading to death within 78 hpi. Infected shrimp were shedding viral DNA, and this shedding reached a peak within 12 h of the time of death. The threshold density for the occurrence of a WSD epidemic in a group infection model was 10 shrimp per 10 L. At this density, the first cases of host-to-host transmission occurred between 30 and 48 hpi in parallel with the occurrence of the first mortalities. Ingestion of WSSV-infected tissues did not significantly increase the number of index cases during an epidemic compared to immersion into water in which cannibalism had occurred. Moreover, the investigation of the role of water, feces, molts, showed that exposing sentinels to rearing water collected from WSSV-infected tanks resulted in a significantly higher probability of infection than exposure to feces or molts. Therefore, we postulate that the occurrence of cannibalism of infected shrimp contributes to indirect water-borne WSSV transmission by the spread of free infectious viral particles.
This research received funding from Flanders Innovation and Entrepreneurship (Belgium).
References:
Giesecke , J., (2017), Modern Infectious Disease Epidemiology: Third Edition, 1-233.
Jewell , N., (2016), Clin. Pharm. Therap., 100 (4), 353.
Thuong, K. et al., (2016). Vet. Research, 47(1).