Infectious Salmon Anemia (ISA) Virus: Infectivity in Seawater under Different Physical Conditions

Abstract

Infectious salmon anemia (ISA) virus (genus Isavirus, family Orthomyxoviridae), present in all major salmon producing countries, is the causative agent for a serious and commercially important disease affecting Atlantic Salmon Salmo salar. Nearly all ISA outbreaks occur in the marine production phase and knowledge about survival time for ISA virions in seawater is crucial for an adequate strategy to combat the disease. To acquire knowledge about this important factor, a study of ISA virus exposed to four different physical conditions was carried out. The virions’ survival was tested in sterile seawater, sterile seawater with normal ultraviolet light radiation (UVR), natural seawater, and natural seawater with UVR. During the 72-h experiment both presence of ISA virus RNA and the infectivity of ISA virions were monitored. The result of this study showed that the infectivity of ISA virions is lost within 3 h of exposure to natural seawater or sterile seawater with UVR. However, it was possible to detect ISA virus RNA throughout the experimental period. This indicates that the effect of both UVR and biological activity of natural seawater limits the survival time of ISA virions under normal conditions. The survival time of ISA virions in sterile seawater was less than 24 h. Based on the available literature and the present study it is not very likely that passive horizontal transmission in seawater over long distances can occur. This is due to the following factors: (1) the effect of UVR and biological activity on ISA virions infectivity found in the present study, (2) the speed and dilution effect in seawater currents in salmon farming areas, (3) the temperature during the major outbreak periods, and (4) the need for an infective dose of ISA virions to reach naive Atlantic Salmon.

Received August 22, 2013; accepted November 7, 2013     

Stability and inactivation of vesicular stomatitis virus,a prototype rhabdovirus

Viruses may remain infectious outside the host cell for considerable time and represent a source of accidental infection if not properly inactivated. In this study, the survival of vesicular stomatitis virus (VSV) in suspension and dried on surfaces was analyzed. In addition, the sensitivity of VSV to disinfectants and physicochemical changes was investigated. VSV showed a notable stability in suspension at 4 °C with virus titers remaining high over several weeks. The presence of serum proteins had a stabilizing effect on virus infectivity, whereas elevated temperatures reduced survival times. VSV dried on polystyrene, glass or stainless steel surfaces remained infectious for at least 6 days at ambient temperature. VSV showed a remarkable resistance to extreme pH in particular in the alkaline range, but could be rapidly inactivated by heating at 55 °C or higher. The virus was highly sensitive to inactivation by commonly used disinfectants such as aldehydes, alcohols, and detergents. The high stability of VSV on surfaces and in suspension may facilitate dissemination of the virus in livestock by contaminated feeding and water troughs, hands, and milking equipment. This knowledge on the sensitivity of VSV to disinfectants will help to set up appropriate hygiene measures.     

Virus survival in slurry: analysis of the stability of foot-and-mouth disease, classical swine fever, bovine viral diarrhoea and swine influenza viruses

Farm slurry can be highly contaminated with viral pathogens. The survival of these pathogens within slurry is important since this material is often distributed onto farm land either directly or after heat treatment. There is clearly some risk of spreading pathogens in the early stages of an outbreak of disease before it has been recognized. The survival of foot-and-mouth disease virus, classical swine fever virus, bovine viral diarrhoea virus and swine influenza virus, which belong to three different RNA virus families plus porcine parvovirus (a DNA virus) was examined under controlled conditions. For each RNA virus, the virus survival in farm slurry under anaerobic conditions was short (generally ≤ 1 h) when heated (to 55°C) but each of these viruses could retain infectivity at cool temperatures (5°C) for many weeks. The porcine parvovirus survived considerably longer than each of the RNA viruses under all conditions tested. The implications for disease spread are discussed.     

Crystalluria. Observations, interpretations, and misinterpretations

Crystalluria results from oversaturation of urine with crystallogenic substance. However, oversaturation may occur as a result of in vitro as well as in vivo events. The microscopic appearance of crystals only represents a tentative identification of their composition because variable conditions associated with their formation, growth, and dissolution may alter their appearance. Definitive identification is dependent on physical methods such as optical crystallography, x-ray diffraction, and electron microscopic analysis.     

Myeloproliferative disease in the dog and cat: definition, aetiology and classification

The term myeloproliferative disease may be applied to all the non-lymphoid dysplastic and neoplastic conditions arising from the haematopoietic stem cell or its progeny. Thus the chronic and acute myeloid leukaemias, thrombocythaemia, megakaryocytic myelosis, myelofibrosis, the myelodysplastic syndromes and some cases of aplastic anaemia may be viewed as variants of a single disease process. This view is useful in explaining the common occurrence of mixed forms of disease or interconversions between the myeloproliferative diseases. This variability is a consequence of the development of all the haematopoietic lineages from a single class of haematopoietic stem cell by progressive differentiation. The aetiology of the myeloproliferative diseases in the domestic animals is uncertain but feline leukaemia virus infection has been implicated in the cat. These conditions may be classified as aplastic anaemia, as preleukaemic dysplastic conditions with variable cytopenias and morphological abnormalities of blood cells, as smouldering leukaemias, or as leukaemias with a frankly leukaemic blood or bone marrow.     

Comparison of the environmental survival characteristics of Salmonella Dublin and Salmonella Typhimurium

To examine possible correlations in bovine Salmonella isolates between environmental survival and serovar-associated epidemiological patterns, bovine field isolates of Salmonella serovars Typhimurium and Dublin (two each) were inoculated into bovine faeces slurry and tested monthly by culture for survival during a six-month period of storage at a variable ambient temperature in a disused animal transporter. Low moisture conditions, where the slurry was dried onto wooden dowels, increased detectable survival of a low-level inoculum by up to five months, compared with wet slurry. A more modest increase of survival time was seen with storage of wet slurry under refrigeration at 4°C. Under both dry and wet conditions, the concentration of culturable Salmonella Typhimurium declined at a slower rate than did that of Salmonella Dublin. Salmonella that was naturally contaminating bovine faeces from farms with Salmonella Typhimurium did not show superior survival times compared with Salmonella Typhimurium that had been artificially inoculated into samples. The differing survival characteristics of the two serovars that was observed in environmental faeces may complement their different modes of infection in cattle. Salmonella Dublin, being a bovine host-adapted strain that establishes chronic infection in some animals, may have less need to survive for a prolonged period outside of its host than does Salmonella Typhimurium.     

Role of water chemistry and stabilizers on the Vero-cells-based infectivity of Newcastle disease virus live vaccine

Newcastle disease virus (NDV) live vaccines are supplied in lyophilized form and usually administered through conventional routes (drinking water, spray, or eye drop) following reconstitution in a diluent. Virus inactivation due to physico-chemical properties of the diluent at the time of administration may lead to vaccine failure. The present study aimed to evaluate the survival of NDV live vaccine strain immersed in 5 pH-amended water samples (pH 5.00, pH 6.00, pH 7.00, pH 8.00, and pH 9.00) by sequential determination of virus infectivity on Vero cells for 3 hours. Minimum reduction in virus infectivity was recorded in the water with neutral or slightly alkaline pH, while the virus was relatively less stable at extreme pH conditions. Maximum reduction of infectivity was observed in the water with pH 9.00 in which the virus was completely inactivated within 3 hours. Addition of stabilizers (Cevamune® or skimmed milk) slightly altered the pH and total dissolved solids (TDS) values of the virus-charged water samples. In the stabilizer-added water samples, minimum reduction in infectivity was observed in the water with neutral pH, followed by the ones with a pH of 8.00, 6.00, 5.00, and 9.00. In all types of water samples, T-90 values (time required for 90% reduction in virus infectivity) were highest (485 minutes) at neutral pH (pH 7.00) and lowest (102 to 134 min) at an extreme alkaline condition (pH 9.00). Results of the present study indicate that water with a pH range of 7.00 to 8.00 is suitable for administration of NDV live vaccines. However, the addition of Cevamune® or skimmed milk may have beneficial effects on preserving the infectivity of the virus, even at extreme pH conditions.     

Survival rate of Suid herpesvirus (SuHV-1, Aujeszky's disease virus, ADV) in composted sewage sludge

Sewage sludge constitutes a source of valuable biogenic raw materials, but it is a carrier of many pathogenic microorganisms and viruses. Subjected to an effective sanitization by means of the process of composting, it is suitable to use in agriculture as fertilizers. The aim of this study was to observe the survival rate of Suid Herpesvirus under the influence of the temperature alone (water bath) as well as in sewage sludge subjected to the process of composting (pile). The samples were taken at different time intervals, and the virus titres were determined. The viruses survived considerably longer under laboratory conditions: at 30 degrees C as long as 21 days, at 40 degrees C - 93 hours, and at 50 degrees C - less than an hour. In the compost pile, in spite of the lack of the thermophylic phase, the total survival time of the viruses ranged from 34 to 44.5 hours, which indicates the vast importance of other physicochemical factors, apart from the temperature, contributing to virus inactivation.     

Persistent infections after natural transmission of bovine viral diarrhoea virus from cattle to goats and among goats

Bovine viral diarrhoea virus (BVDV) is an economically important pathogen of cattle worldwide. Infection of a pregnant animal may lead to persistent infection of the foetus and birth of a persistently infected (PI) calf that sheds the virus throughout its life. However, BVD viruses are not strictly species specific. BVDV has been isolated from many domesticated and wild ruminants. This is of practical importance as virus reservoirs in non-bovine hosts may hamper BVDV control in cattle. A goat given as a social companion to a BVDV PI calf gave birth to a PI goat kid. In order to test if goat to goat infections were possible, seronegative pregnant goats were exposed to the PI goat. In parallel, seronegative pregnant goats were kept together with the PI calf. Only the goat to goat transmission resulted in the birth of a next generation of BVDV PI kids whereas all goats kept together with the PI calf aborted. To our knowledge, this is the first report which shows that a PI goat cannot only transmit BVD virus to other goats but that such transmission may indeed lead to the birth of a second generation of PI goats. Genetic analyses indicated that establishment in the new host species may be associated with step-wise adaptations in the viral genome. Thus, goats have the potential to be a reservoir for BVDV. However, the PI goats showed growth retardation and anaemia and their survival under natural conditions remains questionable.     

Long-term survival of equine surgical colic cases. Part 2: modelling postoperative survival

Colic surgery is a frequently performed operation with high postoperative mortality. This study was undertaken to identify variables associated with decreased postoperative survival. We used data from 321 horse years of postoperative survival time to model the probability of survival following recovery from colic surgery. Continuous variables were modelled using a 6 variable, penalised Cox regression model. This demonstrated approximately linear relationships between survival and the following variables: increase in packed cell volume (PCV), intestinal resection length, time to surgery (interval between onset of colic and surgery) and duration of surgery. No significant decrease in survival was demonstrated with increasing age of the patient or with heart rate. The only categorical variable to be significantly associated with decreased survival was epiploic foramen entrapment. The final, fixed effects Cox proportional hazards model of postoperative survival included the variables epiploic foramen entrapment, PCV, resection length and duration of surgery, each variable adjusted for the nonlinear relationship with time to surgery. Residual variation in postoperative survival attributable to professional personnel (referring veterinary surgeon, anaesthetist and surgeon) was explored by fitting each as a random effects term in the model. Little of the residual variation could be attributed to any category of personnel. Model diagnostics indicated little influence by individual outliers on model parameters and little evidence of subjects poorly predicted by the final model. The study highlights factors influencing the long-term survival of horses recovering from colic surgery and proposes a model that can be used to inform prognosis.     

Survival of Aujeszky's disease virus in frozen pig meat

The survival of Aujeszky's disease virus was studied in muscle, lymph node and bone marrow frozen at -18 degrees C, following infusion of a large dose of the virus into the hindquarter of a freshly killed pig. Previous attempts to induce an adequate viraemia for such studies, using intranasal and intravenous routes of inoculation of large doses of virus in live pigs, were unsuccessful. In frozen meat and marrow, the virus showed a biphasic inactivation curve with time, similar to that seen with cell-cultured virus. Most virus was rapidly inactivated initially but a small population of more stable virus persisted for a considerable period of time. In contrast, virus in lymph node showed a uniform inactivaton rate, like that of the more stable componet only. Virus was not detectable in any of the tissues after 35 days of storage at -18 degrees C.     

Association of QRS duration and survival in dogs with dilated cardiomyopathy: A retrospective study of 266 clinical cases

ObjectiveThe purpose of this study was to investigate the prognostic value of QRS duration in dogs with dilated cardiomyopathy (DCM) by studying its relationship with survival time.MethodsThe medical records of dogs diagnosed with DCM were retrospectively searched for good quality ECG tracings. The QRS duration was measured from the ECG tracing and two different models were used: binary variable (dogs were divided into 2 groups based on a QRS duration of <60 ms or ≥60 ms) and continuous variable. The survival times were analysed by the Kaplan-Meier method and Cox’s proportional hazard model.Results266 dogs met the inclusion and exclusion criteria. A QRS duration ≥60 ms was associated with a reduced survival time compared to those with a QRS duration <60 ms (Hazard Ratio of 1.34, 95% CI 1.05–1.71, P = 0.02). When considered as a continuous variable the Hazard Ratio was 1.015 for each increase in QRS duration of 1 ms (95% CI 1.006–1.024, p = 0.001).Dogs with a QRS duration < 60 ms had a median survival time (IQ range) of 25 weeks (97-65) and dogs with a QRS duration ≥60 ms had a median survival time (IQ range) of 13 weeks (3–34).ConclusionThe measurement of QRS duration is relatively simple to perform from a surface ECG recording. A duration ≥60 ms is associated with shorter survival times in dogs with DCM, which may provide practitioners with additional prognostic information.     

Pleural effusion in cats: 82 cases (1987 to 1995)

Eighty-two cases of feline pleural effusion were identified and reviewed to assess the type of fluid, underlying disease process, predisposing conditions, historical and physical examination findings, laboratory and cytology data, response to treatment and outcome. Pertinent findings included a high occurrence of pleural effusion with mediastinal lymphoma (and other types of intrathoracic neoplasia), pyothorax, cardiomyopathy and feline infectious peritonitis virus infection. Sixteen cases, eight with chylous effusion, had no underlying disease identified. Cats with pyothorax and effusion secondary to trauma had the best prognosis for complete recovery. Otherwise, the outcome was variable and the prognosis was guarded to poor.     

Canine coronavirus inactivation with physical and chemical agents

Canine coronavirus (CCoV) is responsible for mild or moderate enteritis in puppies. The virus is highly contagious and avoiding contact with infected dogs and their excretions is the only way to ensure disease prevention. Since no studies have yet focused on the sensitivity of CCoV to chemical biocides the present investigation examined the efficiency of physical and chemical methods of viral inactivation. CCoV infectivity was stable at +56 degrees C for up to 30 min, but tended to decrease rapidly at +65 degrees C and +75 degrees C. Germicidal ultra-violet (UV-C) light exposure demonstrated no significant effects on virus inactivation for up to 3 days. CCoV was observed to be more stable at pH 6.0-6.5 while extreme acidic conditions inactivated the virus. Two tested aldehydes inactivated the virus but their action was temperature- and time-dependent. The methods for CCoV inactivation could be applied as animal models to study human coronavirus infection, reducing the risk of accidental exposure of researchers to pathogens during routine laboratory procedures.     

The survival of some air-borne animal viruses in relation to relative humidity

The influence of relative humidity (R.H.) on the survival of the following viruses has been examined; feline herpesvirus (FHV); feline calicivirus (FCV); vesicular exanthema virus (VEV); infectious bovine rhinotracheitis virus (IBRV); parainfluenza 3 virus (PI-3 virus); vesicular stomatitis virus (VSV); equine herpesvirus type 1 (EHV-1), equine arteritis virus (EAV); equine rhinovirus (ERV-1), and African swine fever virus (ASFV). ASFV and PI-3 viruses survived well at all relative humidities when sampled 1 s after formation of an aerosol, but after storage of aerosols for 5 min both viruses were found to be sensitive to high R.H. The other lipid-containing viruses (EAV, VSV, FHV, EHV-1 and IBRV) were unstable when stored as aerosols in moist conditions. The picornavirus ERV-1 was the only virus which survived well at high R.H. but poorly on exposure to dry conditions. The caliciviruses VEV and FCV were sensitive to R.H. in the 30–70% range. When subjected to aeration, all of the lipid-containing viruses which were examined lost infectivity but non-lipid viruses, including bovine adenovirus type 1 (BAdV-1), were stable. The addition of 0.1% peptone reduced losses, probably by protecting against surface inactivation. The significance of these findings in relation to possible control measures for viral respiratory disease is discussed.     

A Fresh Look at the Process of Arriving at a Clinical Prognosis. Part 3: Neonatal Illness

Determining the prognosis in a sick newborn foal is complicated by the following three factors: the normal transition from maternal/placental dependence to independence, intrauterine conditions before birth, and the birth process itself. In addition, there are several vulnerabilities and unique characteristics of the neonatal foal that are not shared by older foals or adult horses. However, the same principles of assessing homeostasis apply to establishing a prognosis in a sick neonate, as previously described for the adult. Overall, survival rates for septic critically ill foals generally vary between 60% and 80%. In noncritical yet seriously ill foals—a diverse group sometimes referred to as the “sick, nonseptic foal”—survival rates typically range from 75% to 95% with proper medical care. Long-term survival rates are lower for all categories of sick foals, and subsequent athletic performance may be adversely affected by sepsis or septic arthritis/osteomyelitis.     

Comparison of culling rates among dairy cows grouped on the basis of serologic status for bovine leukemia virus

OBJECTIVE: To determine the association between serologic status for bovine leukemia virus (BLV) and culling rates by use of survival times in a commercial Holstein dairy herd. DESIGN: Longitudinal study. ANIMALS: 593 milking cows. PROCEDURE: Cattle were tested for antibodies against BLV by use of agar gel immunodiffusion or ELISA 4 times each year from 1989 to 1993 and then annually through 1999. Dates of birth, first calving, and culling or death were obtained from Dairy Herd Improvement Association records. Most cows were enrolled in the study on the date of first calving. Survival times were compared among seropositive, seronegative, and seroconverted cows with the Kaplan-Meier method and a Cox regression model stratified on the basis of year of birth. RESULTS: Complete records were available for 593 of 685 (87%) cattle in the dairy herd during the study period. Median survival time for all cows was 31.7 months. Survival times, which correspond to cull rates, did not differ significantly between seropositive and seronegative cattle, whereas cattle that seroconverted during the study had a significantly longer survival time. Year of birth was positively and significantly associated with survival time. CONCLUSIONS AND CLINICAL RELEVANCE: BLV serologic status was not associated with cull rate as measured by survival time in this dairy herd. This finding is in contrast to results of studies that used survival analysis techniques; our results may influence management decisions concerning BLV.     

Experimental bovine pneumonic pasteurellosis: a review

Whenever a 'new' disease is discovered and the putative agent responsible is isolated, it has been customary to attempt to reproduce the disease in similar animals under controlled experimental conditions. If an identical syndrome is produced, then the agent is considered to be responsible for producing the field disease. As early as 1892, Nocard did just that in relation to bovine pneumonic pasteurellosis (shipping/transit fever). His work however, appears to have escaped the attention of many subsequent workers. In the 1930s many workers attempted to reproduce the disease with crude preparations obtained from either sick or dead animals, but most of them failed. After 1950 several agents (bovine herpes virus 1 [BHV1], parainfluenza-3 virus [PI3] and mycoplasmas) were isolated from cases of shipping fever in North America. These, together with physical stress, were thought to be involved in the aetiology and pathogenesis of the disease, with pasteurellae playing the role of secondary invader. Many experimenters then used multiple agents in different combinations, but their degree of success in reproducing the disease was variable. Greater success was achieved when P haemolytica A1 was given to calves four days after exposure to BHV1. This success, although only moderate, reinforced the concept of the secondary role of pasteurellae. After 1977 however, it became increasingly clear that P haemolytica A1 was capable of causing the disease as a primary pathogen, provided that two conditions were fulfilled. First, the calves had to be susceptible, that is, non-immune, and secondly, P haemolytica A1 in the logarithmic growth phase had to be administered to the trachea or lungs in numbers greater than 5 x 10(9) colony forming units.     

A seroepizootiologic study of five viruses in a swine-evaluation station.

This serologic study was done to gain information on the spread, maintenance, and effect upon performance of five porcine viruses. Blood samples were taken from two groups of 8- to 11-week-old pigs from a large number of Indiana swine herds in a performance-testing station 1 week after entry, 7 weeks after entry (one group only), and at slaughter. The sera were tested by indirect fluorescent antibody tests for antibodies to transmissible gastroenteritis virus (TGEV), swine influenza virus (SIV), hemagglutinating encephalomyelitis virus (HEV), porcine adenovirus (PAV), and pseudorabies virus (PRV). Seroconversions to TGEV, HEV, and PAV occurred in a group of pigs entered in May and slaughtered in August (group 1). In the group that was entered in October and slaughtered in January (group 2), pigs developed antibodies to SIV, HEV, and PAV, but not to TGEV. Only 1 of the 434 pigs tested had antibodies to PRV, and there were no seroconversions to this virus. The only statistically valid effect of infection on performance was found in group 1 pigs, which had seroconverted to TGEV during the first 7 weeks of their stay. These pigs gained 0.077 kg less per day than pigs that did not develop antibodies to TGEV during that period. The pattern of serologic reactions was indicative of a relatively slow spread of these viruses in the groups. We interpret this as supporting the concept that a relatively slow spread of these viruses through large groups of pigs kept under conditions that are less than optimum for virus spread may be an important means of their interepizootic survival.     

Survival Analysis of 97 Cats with Nasal Lymphoma: A Multi-Institutional Retrospective Study (1986–2006)

Background: Feline nasal lymphoma (NLSA) is a condition for which no standard of care exists.
Hypothesis: There is no difference in survival times of cats with NLSA treated with single or multimodality therapy.
Animals: Records from 97 cats diagnosed with NLSA were examined.
Methods: The purpose of this retrospective study was to compare the survival times of cats with NLSA treated with radiation therapy (RT) alone, chemotherapy alone, or RT + chemotherapy and identify potential prognostic variables that affected survival. Cats were grouped according to therapy: RT + chemotherapy (n = 60), RT alone (n = 19), or chemotherapy alone (n = 18).
Results: Survival was calculated with 2 methods. The 1st survival analysis (method A) included all cats, but counted only deaths caused by progressive NLSA. The median survival time (MST), regardless of therapy modality, was 536 days. The 2nd survival analysis (method B) also included all cats and counted all deaths, regardless of cause, as events. The overall MST calculated for all deaths was 172 days. A negative independent prognostic variable identified was anemia ( P < .001), and positive independent prognostic variables were a complete response to therapy ( P < .001) and total radiation dose >32 Gy ( P = .03).
Conclusions and Clinical Importance: There were no significant differences in survival times among the 3 treatment groups but these results suggest that the addition of higher doses of RT to a cat's treatment protocol may control local disease and therefore influence survival.