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Viability of ova of Schistosoma mansoni
CORRESPONDENCE
541
America in sand-ballast in 1872, bringing with it a nickname which in its proper home applied to anything small and troublesome (much like the Chinese sha-shih, sand louse). We have thus grown used to this name as applied to the flea in Africa. (b) For exactly the same reasons, the same root-name is used in North and South America for those trombiculid larvae which cause scrub-itch (trombidiasis), and thence for all related larvae. This usage must be respected because it has now been very widely accepted in the considerable literature on trombiculids which has grown up since 1940 ; and also because the name, for mite and flea alike, was invented in the New World anyway. The jigger flea is geographically restricted while the chigger mites are common in every country. Two events are due to bring our usage of these names into prominence shortly° First, the Royal Entomological Society of London is debating the publication of papers devoted to arthropods other than insects, which will encourage many publications on trombiculids. Second, an interest in African trombiculids has been re-awakened by the recent work of JADIN and VERCAMMEN-GRANDJEANin the Belgian Congo : they have indentified about 100 species already, raising the total of known trombiculids from Africa to above 200. The chigger (mite) has thus' come to disturb the peace in what we have (wrongly) felt was the home of the jigger (flea). A name for the parasitic larval stage of trombiculids is emphatically necessary, and the name chigger is recognized everywhere except in England because of our association with medical entomology in Africa. A battle with usage would certainly be lost at this late stage, so may I make an appeal for the acceptance and free use of " chigger " for the larval stage of trombiculids, and " chigoe " or " j i g g e r " (not chigger) for the tungid fleas ? If the subject matter does not make it abundantly clear, then the mention of " chigger mites " or " chigoe (or jigger) fleas " on the first occasion should remove all risk of ambiguity. I am, etc., Institute for Medical Research, Kuala Lumpur, Malaya. 13th October, 1954.
VIABILITY OF OVA OF
J. R. AUDY.
Schistosoma mansoni
SIR,--Experiments were carried out to find out how long ova of S. mansoni can remain dormant and still retain their ability to hatch and produce miracidia capab!e nf i,~fect;~,g snails. A sample of faeces containing many ova was kept in a closed bottle at a temperature of 30°C. At daily intervals a suitable portion was taken, macerated and washed with lake water ; any miracidia that hatched were used to infect Biomphalaria sudanica tanganikana. In all cases (Table) 30 snails were used and each snail was exposed individually to 15 miracidia.
542
CORRESPONDENCE TABLE
Time taken for Time taken for Age of ova miracidia to hatch. snails to shed cerHours Hours cariae. Days Fresh 24 48 72 96
1 1
4 6 Few and sluggish None hatched
21 24 29 30-
No. of snails infected
Per cent. infected
22 21 12 10
73 70 40 33
61 50 49 57
T h e above data show that the quiescent ova gradually lost their ability to hatch when placed in water, and that miracidia f r o m such eggs gradually lost their capacity to infect snails. However, it is of interest to note that miracidia hatched from ova 72 hours old, although very sluggish, were still able to infect snails. This experiment was carried out with the primary object of finding out whether material sent through the post can be used for infection experiments. One may conclude that there is a reasonable chance of success with ova 72 hours old, but ova that are any older are unlikely to produce miracidia. I am, etc., East African Fisheries Research Organization, Jinja, Uganda. 8th October, 1954.
C. C. CRIDLAND,
541
America in sand-ballast in 1872, bringing with it a nickname which in its proper home applied to anything small and troublesome (much like the Chinese sha-shih, sand louse). We have thus grown used to this name as applied to the flea in Africa. (b) For exactly the same reasons, the same root-name is used in North and South America for those trombiculid larvae which cause scrub-itch (trombidiasis), and thence for all related larvae. This usage must be respected because it has now been very widely accepted in the considerable literature on trombiculids which has grown up since 1940 ; and also because the name, for mite and flea alike, was invented in the New World anyway. The jigger flea is geographically restricted while the chigger mites are common in every country. Two events are due to bring our usage of these names into prominence shortly° First, the Royal Entomological Society of London is debating the publication of papers devoted to arthropods other than insects, which will encourage many publications on trombiculids. Second, an interest in African trombiculids has been re-awakened by the recent work of JADIN and VERCAMMEN-GRANDJEANin the Belgian Congo : they have indentified about 100 species already, raising the total of known trombiculids from Africa to above 200. The chigger (mite) has thus' come to disturb the peace in what we have (wrongly) felt was the home of the jigger (flea). A name for the parasitic larval stage of trombiculids is emphatically necessary, and the name chigger is recognized everywhere except in England because of our association with medical entomology in Africa. A battle with usage would certainly be lost at this late stage, so may I make an appeal for the acceptance and free use of " chigger " for the larval stage of trombiculids, and " chigoe " or " j i g g e r " (not chigger) for the tungid fleas ? If the subject matter does not make it abundantly clear, then the mention of " chigger mites " or " chigoe (or jigger) fleas " on the first occasion should remove all risk of ambiguity. I am, etc., Institute for Medical Research, Kuala Lumpur, Malaya. 13th October, 1954.
VIABILITY OF OVA OF
J. R. AUDY.
Schistosoma mansoni
SIR,--Experiments were carried out to find out how long ova of S. mansoni can remain dormant and still retain their ability to hatch and produce miracidia capab!e nf i,~fect;~,g snails. A sample of faeces containing many ova was kept in a closed bottle at a temperature of 30°C. At daily intervals a suitable portion was taken, macerated and washed with lake water ; any miracidia that hatched were used to infect Biomphalaria sudanica tanganikana. In all cases (Table) 30 snails were used and each snail was exposed individually to 15 miracidia.
542
CORRESPONDENCE TABLE
Time taken for Time taken for Age of ova miracidia to hatch. snails to shed cerHours Hours cariae. Days Fresh 24 48 72 96
1 1
4 6 Few and sluggish None hatched
21 24 29 30-
No. of snails infected
Per cent. infected
22 21 12 10
73 70 40 33
61 50 49 57
T h e above data show that the quiescent ova gradually lost their ability to hatch when placed in water, and that miracidia f r o m such eggs gradually lost their capacity to infect snails. However, it is of interest to note that miracidia hatched from ova 72 hours old, although very sluggish, were still able to infect snails. This experiment was carried out with the primary object of finding out whether material sent through the post can be used for infection experiments. One may conclude that there is a reasonable chance of success with ova 72 hours old, but ova that are any older are unlikely to produce miracidia. I am, etc., East African Fisheries Research Organization, Jinja, Uganda. 8th October, 1954.
C. C. CRIDLAND,