Stability of snakehead (Ophiocephalus striatus) rhabdovirus under different environmental conditions

Snakehead rhabdovirus stored in cell culture medium was found to be relatively temperature resistant with ≥ 99.9% reduction in infectivity only occurring after 6 months at 15°C, 6 weeks at 25°C and 10 days at 35°C. At 25°C, virus stability was greatest in the range pH 5–7. Infectivity was less well retained at pH9 and rapidly lost at pH3 and pH11. Stability was poor in serum-free media with a 99.9% reduction in infectivity occurring in less than 48 hours at 25°C in de-ionized water, tap water, balanced salt solutions and artificial seawater.     

Stability of human enteroviruses in estuarine and marine waters.

Studies of the effects of temperature and salinity on the survival of three enteric viruses (poliomyelitis type 1, echovirus-6, and coxsackievirus B-5) under controlled laboratory conditions and in situ indicate that temperature rather than salinity is the critical factor affecting their stability, in that the higher the temperature the more rapid was the loss of viral infectivity. In the laboratory studies, all three viruses were quite stable at 4 degrees C, with infectious virus still detectable after 46 weeks of incubation. In situ studies on virus survival in free-flowing estuarine or marine waters showed that, although the viruses were more labile in natural waters than in the laboratory studies, they persisted for several months, in some cases during the winter months. At all temperatures and salinities, coxsackievirus B-5 was the most stable, echovirus-6 was intermediate, and poliovirus 1 was the least stable of the viruses tested.     

Stability of human enteroviruses in estuarine and marine waters.

Studies of the effects of temperature and salinity on the survival of three enteric viruses (poliomyelitis type 1, echovirus-6, and coxsackievirus B-5) under controlled laboratory conditions and in situ indicate that temperature rather than salinity is the critical factor affecting their stability, in that the higher the temperature the more rapid was the loss of viral infectivity. In the laboratory studies, all three viruses were quite stable at 4 degrees C, with infectious virus still detectable after 46 weeks of incubation. In situ studies on virus survival in free-flowing estuarine or marine waters showed that, although the viruses were more labile in natural waters than in the laboratory studies, they persisted for several months, in some cases during the winter months. At all temperatures and salinities, coxsackievirus B-5 was the most stable, echovirus-6 was intermediate, and poliovirus 1 was the least stable of the viruses tested.     

Infectivity Studies on Cucumber Mosaic Virus Treated with a Clay Material

Montmorillonite, an expansible layer silicate, proved to be the main component of the sediments present in river waters in which cucutnber mosaic virus (CMV), a widespread plant virus, was found. Infectivity assays carried out after treatment of a virus suspension with this clay material, revealed that montmorillonite adsorbed most of the virus-associated infectivity and saved the infectivity of a CMV suspension even after exposure at high ionic strength (lM LiCl).     

Stability of ectromelia virus strain NIH-79 under various laboratory conditions

Ectromelia virus strain NIH-79 was suspended in fetal bovine serum (FBS), minimum essential medium, Hanks' base plus 10% FBS (MEMH + FBS), phosphate-buffered saline (PBS) or PBS plus 50% glycerol (PBS + G). Suspensions were held as liquids or as dry spots at various temperatures. Virus was most stable in FBS and least stable in PBS + G at 4 degrees C, room temperature (23-25 degrees C) or 37 degrees C. Virus held at 4 degrees C was more stable than virus held at higher temperatures, irrespective of supporting medium. Dried spots of blood or serum from ectromelia virus-infected mice remained infectious at room temperature for 11 days and 4 days, respectively. Dried spots of FBS that contained virus were infectious for 5 days, whereas virus retained infectivity for 1 day after drying in other media. Virus was inactivated completely in 10% serum in PBS exposed to 60 degrees C for 30 minutes. Virus was inactivated completely in slices of infected liver and spleen immersed in 10% neutral buffered formalin for 20 hours. These results show that the stability of ectromelia virus strain NIH-79 is medium and temperature dependent and that rapid inactivation occurs after treatments routinely used in diagnostic and research procedures.     

Vector competence of selected South African Culicoides species for the Bryanston serotype of equine encephalosis virus

Equine encephalosis virus (EEV) was recognized and described in the Republic of South Africa in 1967 and subsequent serological studies have shown this orbivirus to be both widespread and prevalent in southern Africa. In the present study it was shown that wild-caught Culicoides (Avaritia) imicola Kieffer (Diptera: Ceratopogonidae) can become infected with and permit the replication of the Bryanston serotype of EEV following membrane-feeding on infective blood containing 5.0 log10 plaque-forming-units (PFU)/ml. The mean prevalence of Bryanston virus infection in C. imicola after 10 days extrinsic incubation at 23.5 degrees C was 22.3% (23/103). The mean infectivity of Bryanston virus in the infected C. imicola increased from 1.3 log10 PFU/midge, in insects assayed immediately after feeding on the blood-virus mixture, to 2.6 log10 PFU/midge in insects assayed after incubation. The virus concentration in individual C. imicola infected with the Bryanston serotype of EEV ranged from 0.7 to 3.6 log10 PFU/midge. Bryanston virus titres higher than 2.5 log10 TCID50, found in individual C. imicola, suggest that this species may be able to transmit this virus to susceptible hosts. Prevalence of virus infection in C. imicola was determined by PFU and microtitration assays on both BHK and Vero cells and confirmation of the Bryanston serotype of EEV was determined by plaque inhibition. No virus replication could be demonstrated in 102 C. nivosus tested after the incubation period, suggesting that not all Culicoides species are equally susceptible to Bryanston virus infection. Other Culicoides species that survived the incubation period and that were negative for the presence of Bryanston virus were C. pycnostictus (42), C. leucostictus (7), C. magnus (2), C. bolitinos (1) and C. bedfordi (1).     

Infectivity-destroying Effect of Humidity for Dried Coliphage T1

Infectivity of dried coliphage T1 has been measured as a function of humidity, temperature, and atmospheric pressure. Loss of infectivity by a factor of 10(4) was caused by water vapor of approximately 40 to 85% saturation when the microorganisms were kept for 3 days at 34 C in evacuated containers. At humidities below 40% and above 90% saturation, no loss of infectivity occurred. At a temperature of 24 C, the infectivity loss was 20-fold. When the virus preparation was kept at 34 C and atmospheric pressure, some loss of infectivity was also found at humidities below 40% and above 90% saturation. Damage to tail proteins or to the phage chromosome is considered as a possible explanation for the inactivation.     

A study of the mode of transmission of maize streak virus by Cicadulina mbila using an enzyme-linked immunosorbent assay

Two batches of Cicadulina mbila were given two distinct acquisition access periods (AAP) (3 h and 50 h) on maize plants infected with maize streak virus (MSV). Infectivity assays on susceptible maize were carried out 1, 3, 10, 17, 26 and 35 days after the AAP. Transmission efficiency was significantly higher for C. mbila subjected to the 50-h AAP. At the same time as the infectivity assays, the amount of MSV in each leafhopper was determined by an indirect double antibody sandwich (IDAS) ELISA. There were more ELISA-positive insects after the 50-h AAP than after the 3-h AAP. In the group given a 3-h AAP, only 7% of the insects tested between day 1 and 35 were found to be positive by ELISA. In contrast, after the 50-h AAP, the majority of C. mbila were positive, yet a decrease in ELISA-positive insects was noticed from day 17 onwards. Using a calibration curve obtained with purified virus, as little as 0.15 ng of MSV per insect could be measured by the IDAS-ELISA. A mean value of 0.36 ng of MSV per C. mbila was found 3 days after the 50–h acquisition, whereas 14 days later there was only 0.20 ng of virus per insect. For comparison, when leafhoppers were kept on infected maize, they displayed substantial accumulation of MSV up to an average of 3.83 ng of MSV per insect after 35 days of continuous acquisition. The amount of virus per insect detected in females was usually greater than the amount detected in males. Our results suggest that MSV does not multiply in C. mbila and contribute to the understanding of the persistence of transmission efficiency in the absence of virus multiplication.     

Effect of temperature on longevity and infection with the nematode Strelkovimermis spiculatus (Nemata: Mermithidae), a parasite of mosquitoes

Strelkovimermis spiculatus is a common parasite of culicid species in Argentina. Effect of temperature on longevity and infectivity of juvenile preparasites of S. spiculatus was determined at 4, 10, 20 and 27 degrees C. Three containers with 100 ml of dechlorinate water and 300 preparasites (12 hour-old), were placed for each day and temperature, during 40 days (total = 480 containers). Survived preparasites were counted on 12 containers per day (three for each temperature). When number of survived preparasites was determined, second instar larvae of Aedes aegypti were added to each container in a 10:1 ratio (preparasites:mosquito) to determine infectivity of daily survived preparasites. Longevity of preparasites decreased at higher temperatures. Maximum longevity of preparasites maintained at 4, 10, 20 and 27 degrees C were 35, 30, 25 and 27 days, respectively. Survivorship of preparasites, exposed to the same temperatures, varied from 57% to 100% at day two, from 21% to 77% at day five and from 9% to 33% at day ten. Infectivity of preparasites maintained at temperatures from 4 to 27 degrees C was always higher than 70%. Extended longevity with maintenance of the infectivity capacity of preparasites, are important attributes to consider S. spiculatus an effective mean of controlling a large number of culicid species between 4 and 27 degrees C.     

Effect of temperature on emergence, survival and infectivity of cercariae of the marine trematode Renicola roscovita (Digenea: Renicolidae)

Marine bivalves harbour a diversity of trematode parasites affecting population and community dynamics of their hosts. Although ecologically and economically important, factors influencing transmission between first (snail) and second (bivalve) intermediate hosts have rarely been studied in marine systems. In laboratory experiments, the effect of temperature (10, 15, 20, 25 degrees C) was investigated on (1) emergence from snails, (2) survival outside hosts and (3) infectivity in second intermediate hosts of cercariae of the trematode Renicola roscovita (Digenea: Renicolidae), a major parasite in North Sea bivalves. Emergence of cercariae peaked at 20 degrees C (2609 +/- 478 cercariae snail(-1) 120 h(-1)) and was considerably lower at 10 degrees C (80 +/- 79), 15 degrees C (747 +/- 384) and 25 degrees C (1141 +/- 334). Survival time decreased with increasing temperature, resulting in 50% mortality of the cercariae after 32.8 +/- 0.6 h (10 degrees C), 26.8 +/- 0.8 h (15 degrees C), 20.2 +/- 0.5 h (20 degrees C) and 16.6 +/- 0.3 h (25 degrees C ). Infectivity of R. roscovita cercariae in cockles Cerastoderma edule increased with increasing temperature and was highest at 25 degrees C (42.6 +/- 3.9%). However, mesocosm experiments with infected snails and cockle hosts in small aquaria, integrating cercarial emergence, survival and infectivity, showed highest infection of cockles at 20 degrees C (415 +/- 115 metacercariae host(-1)), indicating 20 degrees C to be the optimum temperature for transmission of this species. A field experiment showed metacercariae of R. roscovita to appear in C. edule with rising water temperature in April; highest infection rates were in August, when the water temperature reached 20 degrees C. Since another trematode species (Himasthla elongata; Digenea: Echinostomatidae) occurring at the experimental site showed a similar temporal pattern, trematode transmission to second intermediate bivalve hosts may peak during especially warm (> or = 20 degrees C) summers in the variable climate regime of the North Sea.     

Enterovirus inactivation in soil.

The inactivation of radioactively labeled poliovirus type 1 and coxsackievirus B 1 in soils saturated with surface water, groundwater, and septic tank liquor was directly proportional to temperature. Virus persistence was also related to soil type and the liquid amendment in which viruses were suspended. At 37 degrees C, no infectivity was recovered from saturated soil after 12 days; at 4 degrees C, viruses persisted for at least 180 days. No infectivity was recovered from dried soil regardless of temperature, soil type, or liquid amendment. Additional experiments showed that evaporation of soil water was largely responsible for the decreased recovery of infectivity from drying soil. Increased rates of virus inactivation at low soil moisture levels were also demonstrated.     

Enterovirus inactivation in soil.

The inactivation of radioactively labeled poliovirus type 1 and coxsackievirus B 1 in soils saturated with surface water, groundwater, and septic tank liquor was directly proportional to temperature. Virus persistence was also related to soil type and the liquid amendment in which viruses were suspended. At 37 degrees C, no infectivity was recovered from saturated soil after 12 days; at 4 degrees C, viruses persisted for at least 180 days. No infectivity was recovered from dried soil regardless of temperature, soil type, or liquid amendment. Additional experiments showed that evaporation of soil water was largely responsible for the decreased recovery of infectivity from drying soil. Increased rates of virus inactivation at low soil moisture levels were also demonstrated.     

Inactivation kinetics of model and relevant blood-borne viruses by treatment with sodium hydroxide and heat.

To determine the efficacy of a clean-in-place system for the inactivation of viruses present in human plasma, the effect of 0.1 M sodium hydroxide at 60 degrees C on viral infectivity was investigated. Inactivation of the following model and relevant viruses were followed as a function of time: human hepatitis A virus (HAV), canine parvovirus (CPV; a model for human parvovirus B-19) pseudorabies virus (PRV, a model for hepatitis B virus), and bovine viral diarrhoea virus (BVDV, a model for hepatitis C virus and human immunodeficiency virus). Infectivity of CPV was determined by a novel in situ EIA method which will prove useful for studies to validate parvovirus inactivation or removal. Infectivity of BVDV, PRV and CPV were shown to be reproducibly inactivated below the limit of detection by 0.1 M NaOH at 60 degrees C within 30 s. HAV was inactivated to below the limit of detection within 2 min. Treatment with heat alone also resulted in some log reduction for all viruses tested except for CPV which remained unaffected after heating at 60 degrees C for 16 min. Treatment of HAV with hydroxide alone (up to 1.0 m) at 15 degrees C did not lead to rapid inactivation. Collectively, these data suggest that 0.1 M NaOH at 60 degrees C for two min should be sufficient to inactivate viruses present in process residues.     

Persistence of human rhinovirus infectivity under diverse environmental conditions.

The persistence of human rhinovirus type 2 and type 14 infectivity was studied under various laboratory conditions designed to mimic those commonly found in the environment. The effects of temperature, ionic strength, protein content, and evaporation were compared. Both viruses were stable (less than 0.3-log decrease in titer) at 6 and 23 degrees c for 24 h in the liquid state regardless of salt or protein additives; a titer decrease of less than 1.0 log was noted at 37 degrees C. However, evaporation at 37 degrees C reduced virus infectivity by 3.2 to 4.5 logs in buffered water, an effect which could be significantly lessened by the addition of bovine serum albumin in saline (2.0- to 2.9-log decrease in titer). These studies support and extend observations by others that the human rhinoviruses retain sufficient infectivity after drying on hard surfaces to permit their transmission to susceptible persons upon contact.     

Persistence of micronuclei in the marine mussel, Mytilus galloprovincialis, after treatment with mitomycin C

The frequency of micronuclei induced by mitomycin C (MMC) in cells of the gill tissue of the marine mussel, Mytilus galloprovincialis Lmk., was determined over a long period (up to 40-52 days) following treatment. Two doses of MMC (0.5 X 10(-7) and 10(-7) M) were tested at 13 degrees C and 23 degrees C, temperatures representative of the winter and summer thermic conditions of the Mediterranean Sea. In all cases, the frequency of micronuclei was significantly increased by MMC and declined after treatment until it reached a plateau level, significantly higher than the control value. This persisted for a very long time. The frequency of micronuclei induced by a second treatment with MMC performed on the 28th day, did not differ significantly from that produced by the first treatment at the same dose. Temperature did not influence the pattern of the described phenomena to a significant extent. The reason for the persistence of an increased frequency of micronuclei is discussed, and a system is proposed for evaluating the genotoxicity of water pollutants present long before sampling.     

Inactivation of laboratory animal RNA-viruses by physicochemical treatment

Eight commonly used chemical disinfectants and physical treatments (UV irradiation and heating) were applied to both enveloped RNA viruses (Sendai virus, canine distemper virus) and unenveloped RNA viruses (Theiler's murine encephalomyelitis virus, reo virus type 3) to inactivate infectious virus particles. According to the results, alcohols (70% ethanol, 50% isopropanol), formaldehyde (2% formalin), halogen compounds (52ppm iodophor, 100ppm sodium hypochlorite), quaternary ammonium chloride (0.05% benzalkonium chloride) and 1% saponated cresol showed virucidal effects giving more than 99.95% reduction in the infectivity of virus samples of Sendai virus and canine distemper after 10 minutes exposure. There was no significant difference in the effects on the two enveloped RNA viruses. The susceptibility of unenveloped RNA viruses to chemical disinfectants and physical treatments differed greatly from the enveloped viruses. The two unenveloped viruses showed distinct resistance to 50% isopropanol, 2% formalin, 1% saponated cresol and to physical treatments (heating at 45, 56, 60 degrees C, and UV irradiation). These results indicate that using physicochemical methods to inactivate RNA viruses in laboratory animal facilities should be considered in accordance with the characteristics of the target virus. For practical purposes in disinfecting enveloped RNA viruses, 70% ethanol, 0.05% quaternary ammonium chloride and 1% saponated cresol diluted in hot water (greater than 60 degrees C) are considered as effective as UV irradiation. For unenveloped RNA viruses, halogen compounds, more than 1,000 ppm sodium hypochlorite or 260 ppm iodophor are recommended over a period of 10 minutes for disinfecting particles, although these compounds result in an oxidation problem with many metals.     

Sri Lankan passion fruit mottle virus, a potyvirus infecting golden passion fruit in Sri Lanka

A sap-transmissible virus, provisionally named Sri Lankan passion fruit mottle virus (SLPFMV), was isolated from Passiflora edulis f. flavicarpa and shown to induce leaf mottling and distortion in that host. The virus infected 23 species in five plant families with systemic infection being common in the Passifloraceae. Chenopodium amaranticolor was a good local lesion host and Passiflora foetida was a useful systemic host for purification. In P. foetida extracts, SLPFMV lost infectivity after 10 min between 70–75°C, 6–7 days at 20–23°C and at dilutions of 10^--⁵ -W^-6. The virus had flexuous, filamentous particles with a normal length of c. 841 nm. Two polypeptides of mol. wt c. 33 200 and 28 700 were detected in purified virus preparations, and a major species of double-stranded RNA (mol. wt 7.0 × 10⁶), was detected in infected plants. Pinwheels, tubular and laminated inclusions were found in ultrathin sections of infected P. edulis f. plavicurpa and cylindrical inclusions were observed in epidermal strips. SLPFMV was transmitted by the aphids Myzus persicae, Aphis spiraecola, A. gossypü and A. cruccivora after brief acquisition feeds. SLPFMV reacted with antisera to several potyviruses including passion fruit woodiness virus, passion fruit ringspot virus, potato virus Y and watermelon mosaic virus 2 and thus, apparently, is a member of the potyvirus group.     

Survival of duck plague virus in water from Lake Andes National Wildlife Refuge, South Dakota

An isolant of duck plague herpesvirus from the Lake Andes Refuge outbreak was seeded in raw and filter-decontaminated water from two locations on the refuge, held at 4 C, and assayed for infectivity intermittently over a period of 2 mo. From an initial level of about 10(5) PFU per ml, infectivity in the filtered samples uniformly dropped to about 10(4) PFU per ml. Infectivity in the raw samples declined much more rapidly; infectious virus remaining at the end of 2 mo (ca. 10(1) PFU per ml) was only about 0.01% of that originally seeded.     

Long-term survival of human rotavirus in raw and treated river water

This study was aimed at assessing the role of water as a vehicle for rotavirus spread by determining how well these viruses survive in the water environment. A cell culture adapted strain of human rotavirus subgroup 2, grown in MA-104 cells, was used as a model. Virus survival was tested in the following types of water samples, derived from the Ottawa River, at two different times of the year: (i) raw water (RW), (ii) muncipally treated tap water (TW), and (iii) raw water that had been filtered (FW) through a membrane (0.22 micron). The water samples, with approximately 5.0 X 10(4) plaque-forming units (PFU) of the virus, were held at either 4 or 20 degrees C and tested for infectious virus over a period of 64 days. The TW samples had a total and free chlorine content of 0.05 and less than 0.05 mg/L, respectively. The chlorine in these samples was not neutralized before virus contamination. Irrespective of the holding temperature, the virus titre in FW remained essentially unaltered throughout the test period. In TW held at 4 degrees C, there was no significant drop in the virus titre even after 64 days, whereas at 20 degrees C the titre in TW was reduced by about 2 log10 over the same period. Even though the loss of virus infectivity was most rapid in RW held at 20 degrees C, it took about 10 days for a 99.0% reduction in the plaque titre of the virus. These findings, therefore, indicate that rotaviruses can survive for several days in raw and treated river water thus making recreational and potable waters potential vehicles for the transmission of rotavirus infections.     

Persistence of avian influenza viruses in lake sediment, duck feces, and duck meat

The persistence of 3 low-pathogenicity avian influenza viruses (LPAIV) (H4N6, H5N1, and H6N8) and one human influenza virus (H1N1) as well as Newcastle disease virus (NDV) and enteric cytopathogenic bovine orphan (ECBO) virus was investigated in lake sediment, duck feces, and duck meat at 30, 20, 10, and 0°C using a germ carrier technique. Virus-loaded germ carriers were incubated in each substrate, and residual infectivity of the eluted virus was quantified on cell culture after regular intervals for a maximum of 24 weeks. Data were analyzed by a linear regression model to calculate T(90) values (time required for 90% loss of virus infectivity) and estimated persistence of the viruses. In general, the persistence of all of the viruses was highest in lake sediment, followed by feces, and was the lowest in duck meat at all temperatures. For the avian influenza virus subtypes, T(90) values in sediment ranged from 5 to 11, 13 to 18, 43 to 54, and 66 to 394 days at 30, 20, 10, and 0°C, respectively, which were 2 to 5 times higher than the T(90) values of the viruses in the feces and meat. Although the individual viruses vary in tenacity, the survival time of influenza viruses was shorter than that of NDV and ECBO virus in all substrates. The results of this study suggest that lake sediment may act as a long-term source of influenza viruses in the aquatic habitat, while the viruses may remain infectious for extended periods of time in duck feces and meat at low temperatures, allowing persistence of the viruses in the environment over winter.