Out of a total of 58 species of helminthes and protozoan parasitic infections in Korea, so far 38 species were reported as intestinal parasites of man. Quite a few species of the intestinal parasitic infections have long been prevalent throughout the country and this has been a significant public health problem. In this paper, current status and transition of the intestinal parasitic infections in the past years were presented. Chronological reviewing of data show background and prospects of change in the prevalence of infections.
In the national prevalence survey on parasitic infections conducted once every five years since 1971, stool examinations were done by both cellophane thick smear and brine floatation techniques. Every egg positive case of Ascaris lumbricoides and Clonorchis sinensis was further examined by Stoll´s dilution egg counting technique. In 1981, prenatal swab using adhesive cellulose tape was added for Enterobius infection. For protozoan cyst examination conducted by province and city in ´81, fecal specimens were fixed in SAF solution and examined by the formalin ether concentration technique.
High prevalence of parasitic infection in and before the 1960s can be easily understood from the data given by the Ministry of Health and Social Affairs in 1967. From a parasite control point of view, the 1960s was the preparatory period particularly for control of soil transmitted helminthiasis. Several organizations which have contributed to parasite control were founded in this period and the prevention law of parasitic infections was passed in 66. In the 70s, overall prevalence rates of the common intestinal parasitic infections, which were highly prevalent in the past were turned into reduction phase for the first time. The 80s can be said to be an active control period of parasitic infections.
Intestinal helminths
According to the reports of the national prevalence survey on parasitic infections, the prevalence of helminthic infections was 84.3%(number of person examined:24,887) in 71, 63.2(27,178) in 76, and 41.1% (35,018) in 81. By area, the prevalence rate in 81 was 35.1% (20,569) in urban areas and 49.6%(14,447) in rural areas.
Intestinal nematodes
Ascaris lumbricoides
The prevalence of Ascaris infection has decreased significantly in recent years. Among students, the prevalence was 55.4% in 69 and decreased to 4.7% in 83. In the national prevalence surveys, the prevalence decreased to 13.0 % in 81 from 54.9 % in 71. By area, the prevalence decreased to 8.5% in 81 from 46.4% in 71 in urban area and 19.4% in 81 from 59.6% in 71 in rural area. By age, the prevalence has become in recent years relatively even in all age groups, although higher prevalence used to be seen in young age groups of around 10 years old, particularly in the highly prevalent rural areas. By sex, the prevalence was higher in the female than in the male. Unfertilized egg positive rates among the ascariasis cases increased gradually up to 55.4% on the average in 81. The intensity of the infection was also significantly decreased.
Trichuris trichiura
Trichuris infection had also decreased to 23.4 % in 81 from 65.4 % in 71. By area, the decreasing tendency of the prevalence became faster in urban areas than in the rural areas. The prevalence in urban and rural areas in 71 was 69.7 % and 63.1 % respectively and decreased to 19.5% and 29.0% respectively in ´81. By age, the prevalence reached a peak at the 10-14 age group and showed relatively even distribution throughout all age groups. By sex, the prevalence was close in young age groups, but in the 30s or over age group, especially in rural area, the prevalence was significantly higher in the female than in the male. The prevalence has much fluctuated depending in the area The prevalence in rural areas surveyed in the ´80s shows a range between 20.9% and 73.7 % by locality. It is anticipated that the prevalence of Trichuris infection will drop more rapidly, when mass treatment is conducted.
Hookworms:
Hookworm infection by mostly Ancylostoma duodenale and a few by Necator americanus has decreased to a negligible levels in recent years. In the national prevalence surveys, the prevalence was 10.7 % in ´71, 2.2 % in ´76, and 0.5 in ´81. The prevalence was higher in rural areas than in urban areas. Wide application of multi specific anthelminthics in the ascariasis control programs conducted in the past decade appear to have been effective against hookworm infection.
Trichostrongylus orientalis
As in the case with hookworm infection, the prevalence of Trichostrongylus infection has reached a negligible levels. In the national Prevalence surveys, the prevalence was 7.7% in 71, 1.0 % in 76 and 0.2 % in 81.
Enterobius vermicularis
In the national prevalence survey in ´81, the egg positive rate was 12.0%. Higher prevalence is expected when examined repeatedly. The prevalence rate was 10.3% in urban .1rea and 14.6 in rural area. In recent surveys conducted in rural areas among schoolchildren, the prevalence was 32.4% in Gimhae Gun in 82 and 64.1 % in Yeongyang Gun in 83. By age, the egg positive rate was higher in young age groups of around 10 and sharply decreased in age groups of around 20 and then somewhat increased again in middle age groups. By sex, the prevalence was higher in the female than in the male.
Strongyloides stercoralis
Strongyloides stercoralis infection has rarely been found in Korea. Three cases were reported in 1914. And 0.1-0.5%were found infected out of 2,642 persons examined at the prisoner of war camp on Geojedo in 1956. One case was reported in 54 and 82, respectively.
Anisakis spp.
No systematic survey has been conducted for anisakiasis in Korea. So far, only several cases have been found: 1 case in Seoul in 71, 5 cases in Busan in ´81 and 1 case in Busan in 84.
Intestinal trematodes
Metagonimus yokogawai
In the national prevalence survey conducted in 1981, the egg positive rate was 1.2 % on the average. High endemic areas are located in the southwestern part of Korea. The prevalence in Hadong Gun was 29.1% on the average in 79. In a survey conducted in 76, the prevalence was 44.0% in Gwangyang, 55.0% in Gogseung and 29.0 % in Gurye. The infection is closely correlated with raw sweetish consumption in these areas.
Other intestinal trematodes
A human case of Heterophyes heterophyes was reported in 1914. Several species were reported in the 80s: 17 cases of Fibricola seoulensis, 9 cases of Pygidiopsis summa, 8 cases of Heterophyes heterophyes nocens, lcase of Heterophyopsis continua, 2 cases of Stellantchasmus falcatus, 1 case of Stictodora sp.,1 case of Echinosto?; a hortense, and 4 cases of Echinochasmus japonicus. As the intermediate hosts, snakes and frogs play a role for F. seoulensis and fish for the rest of the species.
Intestinal cestodes
Taenia saginata and 7. solium
Egg positive rates in the national prevalence survey were 0.7 % in 76 and 1.1 % in 81. The prevalence in 81 was 0.6 % in urban area and 1.8% in rural area. The proglottid positive rate in Jeju Do was 19.2% on the average. On Udo, Jeju Do in 1983, the egg positive rate among the inhabitants was 2.9%.
Hymenolepis nana
In the national prevalence survey, egg positive rates were 0.6% in 76 and 0.4% in 81. No difference was seen in the prevalence by area and sex.
Hymenolepis diminuta
Infected cases were reported : 3 in ´64 and I in ´66. Egg positive rate in ´81 was 0.01 % in the national prevalence survey.
Diphylobothrium latum
So far, about 30 cases have been reported. The cases have been reported more frequently in recent surveys.
Mesocestoides sp.
A case was reported from a hospitalized patient in Seoul in 67.
Spirometra erinacei
Two cases were reported in 84 following reidentification of the adult worms collected in 74.
Intestinal protozoa
Out of a total of 23 species of human protozoan infections in Korea, 13 species were reported as intestinal protozoa : Entamoeba histolytica, E coli, Endolimax nana, Iodamoeba biitschlii, Dientamoeba fragilis, Giardia lamblia, Chilomastix mesnilii, Embadomonas sp., Enteromonas hominis, Trichomonas ho minis, Isospora belli, I hominis(Sarcocystis hominis), and Balantidium coli.
Since the first report on intestinal protozoan infections in 1925, there have been quite a few survey data on the prevalence of the infection. It was found reviewing the data chronologically that up to the early ´70s the , infection was prevalent around a 30-50j. After that, the protozoan cyst positive rate has shown the tendency of gradual decrease throughout the country. Protozoan cyst survey conducted in Seoul and several provinces in 1981 revealed infection rates of 8.9%(1,310) in Gangweondo, 10.7%(1,703) in Gyenggi Do, 11.7%(1,032) in Jeonra Buk Do, 9.1%(4,116) in Jeonra Nam Do, and 1.4%(5,275) in Seoul.
Entamoeba histolytica
In the survey conducted by province in 81, the cyst positive rate was 0.8 % in Gangweondo, 0.3 % in Gyeonggi Do, 1.4 % in both Jeonra Buk Do and Jeonra Nam Do, and 0.2 % in Seoul.
Giardia lamblia
In the survey by province in ´81, cyst positive rates were 2.2% in both Gyeonggi Do and Jeonra Buk Do, 1.9 % in Jeonra Nam Do, 0.5% in Gangweon Do, and 0.9 % in Seoul.
Balantidium coli
Two cases were reported : one in 1930 and the other in 74.
Isospora belli and I. hominis(Sarcocystis hominis)
Isospora belli was reported : 1 case in ´56 and 3 cases in ´66. I. hominis, recently identified to be synonymous with Sarcocystis hominis, was reported : 3 cases in 6
Other intestinal protozoa
The protozoan parasites other than the above mentioned are generally treated as commercial, although some of them are considered to be pathogenic. The data of ´81 show that about 10 % of the inhabitants are still infected with protozoa.
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