100
A. Pälfi
were inoculated onto 3 primary and 3 permanent monkey kidney cell tube cultures. For
quantitative determinations the MPN-method, as recommended by Chang et al. [3] was
used: 5-5 primary monkey kidney tube cultures (15 in all) were infected by each of the
three different dilutions of this concentrate. After an incubation time of two weeks at
37°C, blind passage was made with the medium of each tube, and another incubation for
2 weeks followed. The virus strains isolated were identified by the HAI (hemagglutinating
inhibition) and neutralization tests.
EXPERIMENTS AND DISCUSSION
(a) Examinations in 1969 (Table 1)
From 28 out of 74 digested sludge samples one or more virus strains (38 per cent)
were isolated. Viruses of one type were demonstrable in 20 of the positive samples, two
types in 5 samples, and three and four types in 2 and 1 samples, respectively. Virus strain
isolates were found to be most abundant in August, November and December. The strains
identified belonged to 11 different serotypes. Reoviruses (35 per cent) and echovirus type
11 (15 per cent) were represented in highest number.
(b) Examinations in 1970 (Table 2)
Out of 82 sludge samples only 13 (15 per cent) proved positive. On the whole 14 virus
strains were isolated, i.e. viruses of two different types were found only in one sample.
The strains were of the following types: 7 proved to be poliovirus type 3, 6 reovirus type
I and 1 echovirus type 11. Virus concentration in the positive samples, as determined by
the quantitative method, was found to be 2.3-19 virus units (MPNCU = Most Probable
Number of Cytopathogenic Units) per 100 ml, at the average 5.4 MPNCU.
Considerable difference is seen in the averages of positive samples taken in 1969 and
1970 (these were 38 and 15 per cent respectively). The number of isolated virus strains
and types show a similar decreasing tendency. In 1969 viruses of 2-4 different types were
isolated from 8 samples (average value 1.4 strains per sample), while in 1970 only one
sample yielded virus isolates belonging to two types (average value 1.08 strain). In 1969
II different types were found, while in 1970 only three types were identified. It is
remarkable that in 1970 poliovirus type 3 was isolated from more than half of the
positive samples. This might be explained by the circumstance that the samples in
question were collected next month following administration of polio-vaccine type 3.
Apart from this the increased heat stability of polioviruses, as observed by Lund [9],
might also have played a role.
By dividing this period of investigation into two parts at about the middle (middle of
June), it is seen that 12 out of 13 positive samples originated from the first period, while
in the second period only the last sample yielded virus (sample taken on October 5). All
samples (on the whole 37) taken between June 11 and September 28 proved negative.
Yet the seasonal maximum of enterovirus circulation coincided with that period and in
the course of 1969 eight out of the thirty collected samples proved positive (among them
one sample contained two virus types, one three types and one four).
On the whole 54 strains, belonging to 12 serotypes, were isolated from the digested
sludge samples during the two years (TaWe 3). Reoviruses (35 per cent), echovirus type
11 and poliovirus type 3 (13-13 per cent) occurred in highest numbers, indicating an
increased resistance of these types. The ratio of the various virus types in waste water
A. Pälfi
were inoculated onto 3 primary and 3 permanent monkey kidney cell tube cultures. For
quantitative determinations the MPN-method, as recommended by Chang et al. [3] was
used: 5-5 primary monkey kidney tube cultures (15 in all) were infected by each of the
three different dilutions of this concentrate. After an incubation time of two weeks at
37°C, blind passage was made with the medium of each tube, and another incubation for
2 weeks followed. The virus strains isolated were identified by the HAI (hemagglutinating
inhibition) and neutralization tests.
EXPERIMENTS AND DISCUSSION
(a) Examinations in 1969 (Table 1)
From 28 out of 74 digested sludge samples one or more virus strains (38 per cent)
were isolated. Viruses of one type were demonstrable in 20 of the positive samples, two
types in 5 samples, and three and four types in 2 and 1 samples, respectively. Virus strain
isolates were found to be most abundant in August, November and December. The strains
identified belonged to 11 different serotypes. Reoviruses (35 per cent) and echovirus type
11 (15 per cent) were represented in highest number.
(b) Examinations in 1970 (Table 2)
Out of 82 sludge samples only 13 (15 per cent) proved positive. On the whole 14 virus
strains were isolated, i.e. viruses of two different types were found only in one sample.
The strains were of the following types: 7 proved to be poliovirus type 3, 6 reovirus type
I and 1 echovirus type 11. Virus concentration in the positive samples, as determined by
the quantitative method, was found to be 2.3-19 virus units (MPNCU = Most Probable
Number of Cytopathogenic Units) per 100 ml, at the average 5.4 MPNCU.
Considerable difference is seen in the averages of positive samples taken in 1969 and
1970 (these were 38 and 15 per cent respectively). The number of isolated virus strains
and types show a similar decreasing tendency. In 1969 viruses of 2-4 different types were
isolated from 8 samples (average value 1.4 strains per sample), while in 1970 only one
sample yielded virus isolates belonging to two types (average value 1.08 strain). In 1969
II different types were found, while in 1970 only three types were identified. It is
remarkable that in 1970 poliovirus type 3 was isolated from more than half of the
positive samples. This might be explained by the circumstance that the samples in
question were collected next month following administration of polio-vaccine type 3.
Apart from this the increased heat stability of polioviruses, as observed by Lund [9],
might also have played a role.
By dividing this period of investigation into two parts at about the middle (middle of
June), it is seen that 12 out of 13 positive samples originated from the first period, while
in the second period only the last sample yielded virus (sample taken on October 5). All
samples (on the whole 37) taken between June 11 and September 28 proved negative.
Yet the seasonal maximum of enterovirus circulation coincided with that period and in
the course of 1969 eight out of the thirty collected samples proved positive (among them
one sample contained two virus types, one three types and one four).
On the whole 54 strains, belonging to 12 serotypes, were isolated from the digested
sludge samples during the two years (TaWe 3). Reoviruses (35 per cent), echovirus type
11 and poliovirus type 3 (13-13 per cent) occurred in highest numbers, indicating an
increased resistance of these types. The ratio of the various virus types in waste water