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KMID : 0353019650020010001
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Korean Journal of Public Health
1965 Volume.2 No. 1 p.1 ~ p.9
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Studies of Malaria parasite Densities Found in Korea in Ralation with the Endemicity
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Abstract
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The author re-examined 616 thick blood films, positive for P.vivax, to make an estimate of the parasite density. These blood films were selected from 990 positive thick blood films collected during 1964.
All films had been stained with the Walker´s method. The selection was made on the quality of the staining. Of the 616 selected blood films, 584 were made by PCD reportion units from fever cases and 32 blood films by personnel of the malaria service during blood surveys.
As most of the thick blood films had been made by layman no sufficient uniformity of thickness of the blood layer of the films could be expected.
Therefore the approximate number of leucocytes seen during the microscopic examination of the slide was counted together with the number of parasites.
The parasite densities were expressed in terms fo "leucocytes per parasite." assuming a leucocyte count of 8000 per mm³, the approximate number of parasites per mm³ was calculated.
Findings and conclusions
1. Parasite density findings related to age
The median parasite density of the different age groups were only slightly different from each other(See fig. 1).
0-23 months : 3,040 2-9 years : 5,200
10-14 years : 5,500 15 years and older : 4,200
In countries with a high malaria endemicity the median parasite density among the younger age groups is normally higher than among the older age groups.
From the above mentioned findings the following conclusions could be drawn: (1) the level of malaria transmission in Korea is low: and (2) the level of immunity developed among the older age groups is low.
2. Parasite density findings related to sex
The median parasite density for males and females was for both 4,860 parasites per mm³(See fig. 2).
3. Parasite density findings related to primary infections and relapses
The median parasite density found in relapsing cases was slightly higher than in primary infected cases , 5,440 and 4,200 parasites/mm³ respectively(See fig. 3).
The median parasite density found in blood films taken from 32 asymptomatic parasite carriers during a blood survey was 1,920 parasites/mm³.
4. Parasite density findings related to for Korean standerds relatively high endemic areas(Area A) and low endemic areas(Area B).
The median parasite density found among 243 positive slides form Area A and among 125 positive slides from Area B was 5,100 and 4,800 parasites/MM³ respectively. This findings indicates that the level of immunity developed by people living in Area A is not higher than in Area B(See fig. 4).
5. Gametocyte findings among 97 classified cases
Of the 54 blood smears from primary infected cases 62.9% contained gametocytes. Among the 43 relapsing cases, 69.8% showed gametocytes in the blood films(See table 6).
From 41 thick films the ratio macrogametocytes per microgametocyte was estimated on 3:1.
6. Low parasite densities in relation with the routine examination technique
The lowest parasite density recorded was 12 parasites per mm³. From the graph of fig. 1 the conclusion can be drawn that on examining an amount of blood of 0.083mm³ containing 660 leucocytes 100% of infections would be found. The routine procedure followed in the laboratory of the malaria service is, however, to examine 100 microscopic fields on an average containing 2,000 leucocytes.
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