Virulence Variation of White Spot Syndrome Virus in Pacific White Shrimp Litopenaeus vannamei

Abstract

The virulence of seven geographic isolates of white spot syndrome virus (WSSV; genus Whispovirus; China [strain CH1995], Nicaragua [strain N2000], Honduras [strain H2000], Ecuador [strains E-L1999 and E-LT2002], and Mexico [strains M-M2001 and M-LP2001]) was compared using a series of challenge experiments, each lasting 10 d. For each isolate, four quantified dilutions (10(-6), 10(7), 10(-8), and 10(-9)) of a viral inoculum were prepared from WSSV-infected shrimp tissue. Each viral inoculum was injected into 10 specific pathogen-free juvenile Pacific white shrimp Litopenaeus vannamei (0.25-1.50 g); controls received injections of marine crustacean physiological saline (3.2%). The minimum dose of viral inoculum that killed 50% of injected shrimp (LD50) was calculated for dilution, tissue concentration, and viral DNA amount. The CH1995 and M-M2001 isolates were the least virulent, with LD50 values of 10(-6) to 10(-7) of viral inoculum. The isolates could be grouped into three virulence clusters (CH1995 and M-M2001; N2000 and E-LT2002; and H2000, E-L1999, and M-LP2001). Virulence clusters were not altered by LD50 values based on viral DNA concentration, although a slight shifting of order in regards to virulence was seen among the three most virulent isolates (E-L1999, H2000, and M-LP2001). Overall, results indicate that there is a measurable virulence difference among WSSV isolates, which may correspond to geographical region.

Evolutionary Trajectory of White Spot Syndrome Virus (WSSV) Genome Shrinkage during Spread in Asia

“…In other words, selection at the between-host level could – in an endemic situation – predominate over selection for faster replication at the within-host level (for examples of conflicting levels of selection see [27], [28]). Regional differences in WSSV virulence [29] and higher within-host competitive fitness of a WSSV variant with a small genome [8] are observations congruent with this hypothesis. Experimental quantification of transmission [30], [31] of geographical isolates under different conditions (e.g., host density, super-infection vs. co-infection) would provide a good test of this hypothesis.…”

Efecto de temperatura y salinidad sobre la supervivencia y desarrollo larval de Litopenaeus vannamei

“…Más aún, el efecto de diferentes temperaturas en combinación con bajas y altas salinidades usado en criaderos comerciales, no ha sido bien analizado durante las etapas larvales de esta especie (2,6). Por tanto, es necesario prestar atención a las variaciones de estos factores abióticos durante el cultivo a gran escala (11), en aguas de baja salinidad por el prominente desarrollo de la camaronicultura tierra adentro (12,13), así como, en aguas con altas salinidades y temperaturas, donde su vulnerabilidad a enfermedades, ha provocado mortalidades y dificultades en la producción del camarón en todas las tallas y edades de distintos proveedores durante la estación calurosa o seca (15,16 …”

“…Therefore, focusing on the variations of these abiotic in large scale breeding (11), in waters with low due to the development of onshore shrimp breeding (12,13), and in waters with high salinity and temperature, where they are vulnerable to disease, have both lead to mortality and difficulties in shrimp production over all sizes and ages bred by different suppliers during the warm or dry season (15,16).…”

Quantitative analysis of the dose–response of white spot syndrome virus in shrimp

“…Viral virulence depends on many factors, a number of which have been explored for WSSV. There is great variation in the virulence of different WSSV genotypes (Laramore, Scarpa, Laramore, & Lin, ; Marks, van Duijse, Zuidema, van Hulten, & Vlak, ; Pradeep, Karunasagar, & Karunasagar, ; Waikhom, John, George, & Jeyaseelan, ; Zwart, Dieu, Hemerik, & Vlak, ). Moreover, during its spread throughout farms in Asia, WSSV appears to have evolved a smaller genome and higher virulence (Dieu et al., ; Marks et al., ; Zwart et al., ).…”

“…Many studies have shown that the rate of WSSV infection depends on virus particle dose (Escobedo‐Bonilla et al., ; Laramore et al., ; Marks et al., ; Prior, Browdy, Shepard, Laramore, & Parnell, ). It has also been suggested that WSSV virus particles might be acting independently during the infection process because dose–response is similar to predictions of the independent action hypothesis (IAH) model (Dieu, Zwart, & Vlak, ).…”