Confirmatory test of active IHHNV infection in shrimp by immunohistochemistry and IHHNV-LongAmp PCR

The presence of endogenous viral elements (EVE) in the penaeid shrimp genome has been recently reported and suggested to be involved in the host recognition of viral invaders. Our previous report of a search for EVE of infectious hypodermal and haematopoietic necrosis virus (IHHNV-EVE) in the Thai Penaeus monodon whole genome sequence project (GenBank accession no. JABERT000000000) confirmed the presence of three clusters of EVE derived from IHHNV in the shrimp genome. This study aimed to compare an immunohistochemistry method (IHC) and a PCR method to detect infectious IHHNV infection in shrimp. First, specimens collected from farms were checked for IHHNV using three PCR methods; two methods were recommended by WOAH (309 and 389 methods), and a newly established long-range PCR for IHHNV (IHHNV-LA PCR) targeting almost the whole genome (>90%) of IHHNV. Among 29 specimens tested, 24 specimens were positive for WOAH methods (at least one method). Among 24 WOAH-positive specimens (WOAH+), there were 18 specimens with positive IHHNV-LA PCR method (WOAH+/LA+), six specimens with negative IHHNV-LA PCR method (WOAH+/LA-). Six specimens were negative for all methods (WOAH-/LA-). The positive signals detected by IHC method were found only in the specimens with WOAH+/LA+. The results suggest that the WOAH+/LA- specimens were not infected with IHHNV, and the positive WOAH method might result from the EVE-IHHNV. The study recommends combining the IHHNV-LA PCR method and IHC with positive PCR results from WOAH's recommended methods to confirm IHHNV infection.

A new genotype of decapod hepanhamaparvovirus 1 (DHPV) from cultured Penaeus vannamei in South Korea

Decapod hepanhamaparvovirus 1 (DHPV), also known as hepatopancreatic parvovirus (HPV), has caused death in larvae or stunted growth in juveniles of cultured shrimp. To date, 4 genotypes (genotype I, II, III, and IV) have been reported from various shrimp species and various geographical regions. In the present study, we isolated 2 types of DHPV (GHPV-Goseong and DHPV-Geoje) from cultured Penaeus vannamei in Korea. Based on the capsid protein (VP) amino acid sequences, DHPV-Goseong was highly identical to previously reported DHPV genotype IV in Taiwan and Korea. Different from DHPV-Goseong, DHPV-Geoje showed approximately 63% similarity with DHPV genotype I, II, III and 84% similarity with DHPV genotype IV, suggesting an independent new genotype of DHPV (genotype V). Further research is needed to elucidate the origin and biological meanings of the present new genotype.

Coinfection with Yellow Head Virus Genotype 8 (YHV-8) and Oriental Wenrivirus 1 (OWV1) in Wild Penaeus chinensis from the Yellow Sea

At present, there are few studies on the epidemiology of diseases in wild Chinese white shrimp Penaeus chinensis. In order to enrich the epidemiological information of the World Organisation for Animal Health (WOAH)-listed and emerging diseases in wild P. chinensis, we collected a total of 37 wild P. chinensis from the Yellow Sea in the past three years and carried out molecular detection tests for eleven shrimp pathogens. The results showed that infectious hypodermal and hematopoietic necrosis virus (IHHNV), Decapod iridescent virus 1 (DIV1), yellow head virus genotype 8 (YHV-8), and oriental wenrivirus 1 (OWV1) could be detected in collected wild P. chinensis. Among them, the coexistence of IHHNV and DIV1 was confirmed using qPCR, PCR, and sequence analysis with pooled samples. The infection with YHV-8 and OWV1 in shrimp was studied using molecular diagnosis, phylogenetic analysis, and transmission electron microscopy. It is worth highlighting that this study revealed the high prevalence of coinfection with YHV-8 and OWV1 in wild P. chinensis populations and the transmission risk of these viruses between the wild and farmed P. chinensis populations. This study enriches the epidemiological information of WOAH-listed and emerging diseases in wild P. chinensis in the Yellow Sea and raises concerns about biosecurity issues related to wild shrimp resources.

Concurrent infection of a novel genotype of hepatopancreatic parvovirus and Enterocytozoon hepatopenaei in Penaeus vannamei in Taiwan

Hepatopancreatic parvovirus (HPV) and Enterocytozoon hepatopenaei (EHP) are emerging and reemerging pathogens in shrimps. In the present study, a novel genotype of HPV concurrently infected with EHP in Penaeus vannamei in Taiwan leading to severe atrophy and damage of hepatopancreas were confirmed by histopathology, in situ hybridization, and PCR. The novel genotype of HPV exhibited 66%-69.5% sequence identities with all known HPVs and carried unique amino acid deletions and insertions in the VP gene. According to phylogenetic analysis, the Taiwan HPV isolates were classified as the genotype IV. The present study not only provided the histopathological and molecular proof of HPV and EHP co-infection in Taiwan, but also revealed the importance of investigating the geographical expansion of novel HPV genotypes.

Studies on infectious myonecrosis virus (IMNV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) in cultured penaeid shrimp in Egypt

The present study aimed to diagnose infectious myonecrosis virus (IMNV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) among cultured penaeid shrimp (Penaeus semisulcatus, n = 120) collected from private farms in 2 Egyptian provinces (Damietta and North Sinai) along the Mediterranean coast. The collected shrimp were subjected to clinical examination, histopathology, molecular characterization, and phylogenetic analysis. Most of the shrimp infected with IMNV showed a distinctive appearance resembling cooked shrimp and white necrosis on distal abdominal segments and tail fans. Simultaneously, IHHNV-infected cases displayed opaque abdominal muscles, white milky to buff mottling on the shell, and a pathognomonic runt-deformity syndrome. Histopathological examination of infected specimens revealed muscular edema, hemocyte infiltration, deformities, Zenker's necrosis, and eosinophilic intra-nuclear inclusion bodies (Cowdry type A). PCR results gave predictable amplicon sizes of 139 and 81 bp and confirmed the presence of IMNV and IHHNV with a total prevalence of 37.5 and 25%, respectively. A homology search by BLAST analysis showed that the retrieved isolates putatively belonged to IMNV and IHHNV based on 96.3 to 97% nucleotide identity to the corresponding open reading frame gene of each virus. The phylogenetic analysis clearly showed genetic similarity and cross-lineage between our isolates and other isolates from Egypt, the USA, Brazil, Indonesia, China, Korea, Taiwan, and Ecuador. In conclusion, gross inspection and histopathology may aid in the diagnosis of viral diseases; however, molecular tools are indispensable for confirming a possible infection. The current study recommends strict regulations during live shrimp transportation and implementing health control certificates over all imports and exports, especially in developing countries, including Egypt.

Mosquito cells (C6/36) fail to support the complete replication of Penaeus merguiensis hepandensovirus

Mosquito cell lines (C6/36) were reported in the literature to support the propagation of Penaeus monodon hepandensovirus (PmoHDV). We aim to evaluate the susceptibility and viral propagation of P. merguiensis hepandensovirus (PmeHDV) which is ∼22% different to PmoHDV in Aedes albopictus cell line (C6/36). Cellular changes in the infected cell culture were detected. Vacuole formation was seen in both infected and uninfected cell cultures. The average number of disrupted cellular membranes in the infected cells (presumptive dead cells) was significantly higher than that of uninfected cells at passage two (F=9.749, d.f. 1, 22, p<0.05). Using a proliferation assay, light absorption of infected cells peaked at 2weeks post-infection (O.D.=0.27) but was significantly lower than that of the uninfected groups (O.D.=0.37) (F=6.879, d.f. 1, 94, p<0.05) suggesting hindered cell growth. PCR of the serial passages of the infected cell cultures indicated weak positive results for PmeHDV infection and TaqMan quantitative PCR confirmed that the average number of viral copies declined from 3.8×10⁵ to 5.69×10² copies per μL and the mean of cycle times increased from 19.26 to 27.63. These results are interpreted to mean C6/36 allows the initial stage of PmeHDV replication, but the virus was incapable of using C6/36 for patent replication of its' virions.

Seasonal abundance of vectors at outdoor environments in endemic and nonendemic districts of dengue in Kaohsiung, South Taiwan

This study was designed to determine the seasonal variation in abundance of dengue vectors at open spaces, empty houses, parks, and markets in endemic and nonendemic districts of dengue. Ovitraps were placed in these sites from March 2003 to January 2004 in Kaohsiung Area (Kaohsiung City and Kaohsiung County), South Taiwan. The index peaked in May, June, and September in the endemic districts and in May and October in nonendemic districts. The egg production of the vectors increased from April on and peaked in September. Aedes albopictus had a significant higher proportion than A. aegypti throughout the study period and in both districts. Although ovitrap indices at open spaces, empty houses, and parks were significantly higher than those in nearby households, no significant difference was found between markets and households. Moreover, the outdoor ovitrap index was significantly higher than the indoor one. No significant difference was found between the endemic and nonendemic districts in egg production, vector maturation, vector abundance at the outdoor environments, or nearby households. These findings indicate the importance of the environmental conditions surrounding the human dwelling sites in the transmission of dengue. Measures applied to remove dengue vectors should include these sites but also outdoor environments as well.

Different responses to infectious hypodermal and hematopoietic necrosis virus (IHHNV) in Penaeus monodon and P. vannamei

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is widespread in cultured Penaeus monodon and P. vannamei in Thailand. It causes runt-deformity syndrome that is characterized by physical abnormalities and stunted growth in P. vannamei, but causes no apparent disease in P. monodon. In both species, the virus may produce Cowdry Type A inclusions in tissues of ectodermal and mesodermal origin, but these are common in P. vannamei and rare in P. monodon. The virus can be more easily detected in both species by IHHNV-specific PCR primers. By in situ hybridization (ISH) using specific IHHNV probes, fixed phagocytes associated with myocardial cells tended to show strong positive reactions in both shrimp species. Ovarian and neural tissue (neurons in the nerve ganglia and glial cells in the nerve cord) were ISH positive for IHHNV only in P. vannamei. By transmission electron microscopy, necrotic cells were found in the gills of IHHNV-infected P. vannamei, while paracrystalline arrays of virions and apoptotic cells rather than necrotic cells were found in the lymphoid organ of IHHNV-infected P. monodon. Thus, it is possible that apoptosis in P. monodon contributes to the absence of clinical disease from IHHNV. These findings reveal different responses to IHHNV infection by the 2 shrimp species. A curious feature of IHHNV infection in P. monodon was inconsistency in the comparative viral load amongst tissues of different specimens, as detected by both ISH and real-time PCR. This inconsistency in apparent tissue preference and the reasons for different cellular responses between the 2 shrimp species remain unexplained.

Geographical information system (GIS) in investigation of an outbreak

An outbreak of fever in a village in southern India was reported on 1st September, 2001. The first reported case presented with epistaxis and a platelet count of 27000h(1)/mm3. Clinical, laboratory and entomological evidence supported a diagnosis of dengue fever. One third of the village was affected and 3.7 % of the population presented with haemorrhagic symptoms; none were fatal. Five acute cases tested for dengue specific IgM showed that two were positive. The larvae of Aedes aegypti were discovered from domestic water collections in the village. Spatial analysis done with the help of Geographical Information Systems software (GIS) demonstrated a centrifugal spread of cases from the most affected street until it involved the entire village. Spatial analysis revealed that cases occurred in clusters and that these could not have occurred by chance. This was our first experience in producing a geo-referenced map of a village area and in spatial analysis. GIS is a novel and simple tool for outbreak investigations and the spatial analyst adds additional information to the data collected. Control of adult mosquitoes and larvae prevented the outbreak from spreading to an adjacent village.

Can plants use an entomopathogenic virus as a defense against herbivores?

It is by now well established that plants use various strategies to defend themselves against herbivores. Besides conventional weapons such as spines and stinging hairs and sophisticated chemical defenses, plants can also involve the enemies of the herbivores in their defense. It has been suggested that plants could even use entomopathogens as part of their defense strategies. In this paper, we show that Brassica oleraceae plants that are attacked by Myzus persicae aphids infected with an entomopathogenic parvovirus (M. persicae densovirus) transport the virus through the phloem locally and systematically. Moreover, healthy aphids that fed on the same leaf, but separated from infected aphids were infected via the plant. Hence, this is proof of the principle that plants can be vectors of an insect virus and can possibly use this virus as a defense against herbivores.

Aedes aegypti transducing densovirus pathogenesis and expression in Aedes aegypti and Anopheles gambiae larvae

Aedes aegypti densovirus (AeDNV) is a small DNA virus that has been developed into an expression and transducing vector for mosquitoes [Afanasiev et al. (1994) Exp Parasitol 79: 322-339; Afanasiev et al. (1999) Virology 257: 62-72; Carlson et al. (2000) Insect Transgenesis: Methods and Applications (Handler, A.M. & James, A.A., eds), pp. 139-159. CRC Press, Boca Raton]. Virions carrying a recombinant genome expressing the GFP gene were used to characterize the pathogenesis of the virus in 255 individual Aedes aegypti larvae. The anal papillae of the larvae were the primary site of infection confirming previous observations (Afanasiev etal., 1999; Allen-Muira et al. (1999) Virology 257: 54-61). GFP expression was observed in most cases to spread from the anal papillae to cells of the fat body, and subsequently to many other tissues including muscle fibers and nerves. Infected anal papillae were also observed to shrink, or melanize and subsequently fall off in a virus dependent manner. Three to four day-old larvae were less susceptible to viral infection and, if infected, were more likely to survive into adulthood, with 14% of them still expressing GFP as adults. Higher salt concentrations of 0.10-0.15 M inhibited viral infection. Anopheles gambiae larvae also showed infection of the anal papillae (17%) but subsequent viral dissemination did not occur. The persistence of the reporter gene expression into adulthood of Aedes aegypti indicates that transduction of mosquito larvae with recombinant AeDNV may be a means of introducing a gene of interest into a mosquito population for transient expression.

Venereal and vertical transmission of the Aedes albopictus parvovirus in Aedes aegypti mosquitoes

Following per oral infection of Aedes aegypti larvae with Aedes albopictus parvovirus (AaPV), infected males and females adults were tested for their ability to transmit the virus venereally and vertically, respectively. Both types of transmission were observed. A low percentage (2.2%) of AaPV-free females were found contaminated by the virus after mating with AaPV-infected males. Although no significant difference was observed in the fecundity of orally infected and virus-free females, 17.1% of infected ones died before egg laying, whereas no mortality occurred during the same period in virus-free females. There was a clear relationship between the virus titer in the orally infected females and both mortality and infection in their offspring. The virus titer averaged 10(6.2) 50% tissue culture infective doses (TCID50s) in F1 females and 10(3.3) TCID50 in F1 females. Nevertheless, AaPV did not persist in an experimentally infected population of mosquitoes beyond the second generation.