• Parasites, Hosts and Diseases
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• v.47 no.1
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• pp.7-11
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• 2009

Cryptosporidium parvum is a well-known waterborne and opportunistic intracellular protozoan parasite that causes diarrheal illness. In this study, we quantitatively investigated reduction of the infectivity of C. parvum after gamma irradiation and repair of the infectivity during incubation time after irradiation. C. parvum oocysts were subjected to gamma irradiation at various doses (1, 5, 10, and 25 kGy), and the in vitro infectivity was measured by real-time PCR every day up to 7 days after irradiation. The in vitro infectivity of C. parvum on human ileocecal adenocarcinoma cells (HCT-8) was effectively reduced (> $2\;{\log}_{10}$) by irradiation at 10kGy or more. However, in the experiment to find out repair of the infectivity, recovery was not noted until day 7 post-incubation.

• Journal of Preventive Medicine and Public Health
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• v.53 no.2
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• pp.67-69
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• 2020

Controversy remains over whether the coronavirus disease 2019 (COVID-19) virus may have infectivity during the incubation period before the onset of symptoms. The author had the opportunity to examine the infectivity of COVID-19 during the incubation period by conducting an epidemiological survey on a confirmed patient who had visited Jeju Island during the incubation period. The epidemiological findings support the claim that the COVID-19 virus does not have infectivity during the incubation period.

• Journal of Environmental Health Sciences
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• v.34 no.5
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• pp.382-386
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• 2008

This study was designed to establish the time frame of viability and infectivity of Cryptosporidium, when the Cryptosporidium is discharged to the aquatic environment. Changes in viability and infectivity of Cryptosporidium in relation to temperature and pH were investigated during winter (Dec 05-Feb 06) using semipermeable cellulose tubes containing infective Cryptosporidium. Infectivity was maintained at 50% after 30 days and almost completely lost after 50 days. It was also established that viability was maintained at about 8% after 90 days.

• Food Science and Biotechnology
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• v.16 no.3
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• pp.398-403
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• 2007

The effectiveness of phage biocontrol depends on the activity of bacteriophage in a given environment. In order to investigate the infectivity and the stability of bacteriophages in representative environments, three virulent phages, Listeria phage A511, Salmonella phage Felix O1, and Escherichia coli phage T7, were subjected to different temperatures, pHs and salt concentrations (NaCl). Phage infectivity was also determined in the presence of divalent cations ($Mg^{2+}$ or $Ca^{2+}$). As a result, three phages exhibited a wide range of survival rates under various environments. Phage infectivity was directly correlated with bacterial growth under the applied conditions. One exception was Felix O1 that did not kill Salmonella grown in low pH (4.5). The failure was attributed to defective adsorption of Felix O1. This finding is significant as it provides an explanation for the inefficient phage biocontrol. Therefore, such information is crucial to improve phage biocontrol of pathogens.

• Journal of fish pathology
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• v.31 no.2
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• pp.81-85
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• 2018

Fetal bovine serum (FBS) is an essential element of cell growth and can also affect the viral replication. In this study, we tried to find out whether FBS concentration affects the viral infectivity titer of IHNV and IPNV. EPC cells were suspended with MEM supplemented with various concentrations of FBS (MEM0, MEM2, MEM5 and MEM10) and cultured in 96-well plate. Each virus was 10-fold diluted virus and inoculated in 96-well plate. The highest infectivity titer of IHNV was $10^{7.88}\;TCID_{50}/mL$ in 96-well plate using MEM5 and the lowest one was $10^{7.30}\;TCID_{50}/mL$ in 96-well plate using MEM10. The highest infectivity titer of IPNV was $10^{7.47}\;TCID_{50}/mL$ in 96-well plate using MEM5 and the lowest one was $10^{6.97}\;TCID_{50}/mL$ in 96-well plate using MEM10. This study showed that not only 0% FBS but 10% FBS leads low infectivity titer of IHNV and IPNV. Therefore, it is considered that the desirable concentration of FBS is 2% or 5% for measurement of infectivity titer of IHNV and IPNV.

• Korean Journal of Veterinary Research
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• v.38 no.1
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• pp.161-166
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• 1998

Fasciola hepatica eggs were obtained from the bile of infected cattle at a local abattoir. Metacercariae(MC) were produced using Lymnaea viridis, the intermediate host of the parasite. They were stored in distilled water at refrigerator($3{\sim}5^{\circ}C$) and at room temperature($22{\sim}27^{\circ}C$). The viability and infectivity of the MC were determined at monthly intervals for 12 months. The viability was determined by both microscope and excystation, and the infectivity by infecting mice. The MC stored at room temperature had a high viability up until 60 days, and thereafter the viability declined rapidly ; at day 120, only 2.5% of the MC were excysted. Most of the MC stored at refrigerator retained the viability up until 90 days, and thereafter the viability declined slowly ; about half of them were viable at day 210 and 5% of them retained the viability until day 270. The survival rates of the MC determined by microscope were always higher than those determined by excystation(p<0.05). The infectivity of the MC wisely followed the viability at the two different storage temperatures. Most of the mice infected orally with the MC died within 3-9 weeks of acute fasciolosis.

• Fisheries and Aquatic Sciences
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• v.1 no.1
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• pp.79-81
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• 1998

To investigate the influence of originated host and water temperature on the infectivity and growth of Microcotyle sebastis, juveniles of Schlegel's black rockfish (Sebastes schlegeli) were exposed to the eggs of M. sebastis originated from. Schlegel's black rockfish and black rockfish (Sebastes inermis) at $10^{\circ}C$ and $10^{\circ}C$. There were significant differences between the two isolates in the infectivity of eggs, and the growth of worms. The growth of M. sebastis was significantly affected by water temperature, and worms grew faster in $20^{\circ}C$ than in $10^{\circ}C$.

• Parasites, Hosts and Diseases
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• v.40 no.1
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• pp.55-58
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• 2002

The effects of exogenous glucose in artificial spring water (ASW) were studied on the survival and infectivity of Schistosoma mansoni cercariae. The mean percent survival of cercariae maintained in 1% glucose in ASW for 36 and 48hr was significantly greater than that of cercariae maintained identically in ASW. Cercariae maintained in ASW with or without glucose for 24hr, fixed in neutral buffered formalin, and stained in Oil Red O. showed an accumulation of neutral lipid in the tail. Cercariae maintained as described above and stained in periodic acid-Schiff exhibited depleted glycogen, mainly from the tail. Cercariae maintained in ASW with glucose for 24hr did not resynthesize glycogen. Cercariae maintained in ASW with glucose for 24hr were as capable of infecting male FVBN202 mice as were freshly emerged cercariae, and increased the percent of worm recovery. Exogeneous glucose added to ASW prolonged the survival of S. mansoni cercariae and increased infectivity in terms of worm recovery.

• Korean Journal of Microbiology
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• v.3 no.1
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• pp.24-26
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• 1965

In July, 1963, a virulent outbreak of late blight in the potato field of Daekwanlyung area was studied and it was known as epidemics. Two stocks are $T_1$ and $T_1$ of Phytophthora infestans (Mont.) De Bary which isolated from Irish Cobbler were inoculated at field and green house respectively by cutted leaves method. Two strains have been distinguished in reactions to leaves: $T_1$: Irish Cobbler (r), Morin No. 1 (r) have shown infectivity of disease and Kennebec ($R_1$), 1512-C(16) ($R_2$), Pentland Ace ($R_3$) and Hokkai No. 17 ($R_4$) have not shown infectivity of disease; $T_1$: Irish Cobbler (r), Norin No. I (r) and Kennebec ($R_1$) have shown infectivity of disease and 1512-C (16) ($R_2$), Pentland Ace ($R_3$) and Hokkai No. 17($R_4$) have not shown infectivity of disease. Both are the first record of race O and race 1 of Phytophthora infestans (Mont.) De Bary in Korea.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.5
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• pp.415-420
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• 2010

In Korea, oysters are used as an ingredient of Kimchi (Korean pickled cabbage) in early winter. Although viral contamination of oysters, including contamination by norovirus, can provoke gastroenteric illness, little is known of the epidemiological relationship to outbreaks. We postulated that Kimchi ripening can reduce the infectivity of norovirus, in order to test this hypothesis, we carried out a model experiment. Since norovirus is currently regarded as non-culturable, feline calicivirus (FCV) was used as a surrogate to examine the activation of norovirus with Kimchi ripening. In commercial well-prepared Kimchi, the infectivity ($TCID_{50}$) of FCV decreased by 2 log every 12 hours and reached the limit of detection after 48 hours during over-aging at $25^{\circ}C$. During storage at $4^{\circ}C$, the infectivity ($TCID_{50}$) of FCV decreased slowly and reached 5.00 $TCID_{50}$ after 48 hours. The low pH appears to affect the infectivity of FCV directly via organic acids produced by ripening during over-aging and storage. In neutralized lab-prepared Kimchi (pH 7.0), the infectivity ($TCID_{50}$) of FCV also decreased and reached the limit of detection after 72 hours at $4^{\circ}C$. This indicates that there are substances beside organic acids in Kimchi that originate from the raw materials and are produced during ripening. Among the raw materials, salt-fermented anchovies and garlic showed high direct antiviral activity. The main factor decreasing the infectivity of FCV in Kimchi was the high acidity caused by organic acids, regardless of the type, produced by ripening. Furthermore, unknown secondary products of microorganisms associated with Kimchi ripening and antiviral materials originating from raw material might contribute to the decreased infectivity of FCV, the surrogate of norovirus.