A review of investigations of the habits and pathogenicities of the common anophelines of Hongkong

A review of investigations of the habits and pathogenicities of the common anophelines of Hongkong

91 TRANSACTIONS TROPICAL Vol. 45. OF THE ROYAL SOCIETY (IF MEDICINE AND HYGIENE. No. I. August, 1951. A REVIEW OF INVESTIGATIONS OF THE HABITS AND P...

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91 TRANSACTIONS TROPICAL Vol. 45.

OF THE ROYAL SOCIETY (IF MEDICINE AND HYGIENE. No. I. August, 1951.

A REVIEW OF INVESTIGATIONS OF THE HABITS AND PATHOGENICITIES OF THE COMMON ANOPHELINES OF HONGKONG. BY R. B. J A C K S O N ,

O.B.E., M.D., D.P.H.,

Malariologist, Hongkong, 1930-38.

SITUATION, DETAILS, CLIMATE~ TOPOGRAPHY OF THE COLONY.

The Colony is situated to the south of the sub-continent of China in latitude 22 ° North and longitude 114 ° East. It comprises the Island of Hongkong, the peninsula of Kowloon on the adjacent mainland and the New or Leased Territories bordering on the peninsula, the total area being about 356 square miles ; the area of the island is 36 square miles. T h e climate is i n f l u e n c e d b y t h e m o n s o o n s . T h e n o r t h - e a s t m o n s o o n blows f r o m N o v e m b e r until April, d u r i n g w h i c h p e r i o d t h e w e a t h e r is d r y a n d cool. F r o m M a y until O c t o b e r , the season of t h e s o u t h - w e s t m o n s o o n , t h e air is heavily l a d e n w i t h m o i s t u r e a n d t h e climate is h o t a n d d a m p . April a n d O c t o b e r m a y b e r e g a r d e d as t r a n s i t i o n a l m o n t h s c o r r e s p o n d i n g to s p r i n g a n d a u t u m n . M o s t of the rainfall occurs d u r i n g t h e p e r i o d M a y to October, s o m e t i m e s in p r o l o n g e d a n d h e a v y showers. T h e average a n n u a l rainfall is 85.72 inches. T h e m e a n a n n u a l t e m p e r a t u r e is 72 ° F. D u r i n g t h e h o t m o n t h s t h e average m a x i m u m t e m p e r a t u r e is 87 ° F. a n d t h e r e is little difference t h r o u g h o u t t h e 24 h o u r s . D u r i n g t h e cool m o n t h s t h e r a n g e of t e m p e r a t u r e is f r o m 70 ° F. to 45 ° F., w i t h a n average of 66 ° F. T o p o g r a p h i c a l l y , t h e C o l o n y m a y b e said to consist of a series of g r a n i t e ridges, rising o f t e n to altitudes of 1,000 feet. B e t w e e n t h e ridges, a n d t h e spurs arising f r o m t h e m , are valleys c o n t a i n i n g r o c k - b e d d e d streams w i t h b o u l d e r s of various sizes' a n d shapes. T h e hillsides are covered w i t h grass, s h r u b s , a n d small trees. A f t e r leaving t h e hills t h e s t r e a m s o n t h e island r u n s h o r t courses to t h e sea. I n some t h e g r a d i e n t is steep, i n others flat ; a b r u p t changes i n level are n o t u n c o m m o n . N a r r o w valleys are t h e rule o n t h e island, b u t o n the m a i n l a n d wide valleys in rice cultivation are f r e q u e n t l y m e t with.

This re¥iew has been compiled from the Annual Reports of the Malaria Bureau, 1931-37.

92

ANOPHELINES OF HONGKONG

Four species of anophelines were commonly met with. A. maculatus, A. minimus, A. hyrcanus, A. jeyporiensis ; of the two latter, A. hyrcanus var sinensis (Wied), A. jeyporiensis var candidiensis (Koidzumi) were the only representatives of these species recorded. QUEEN MARY HOSPITAL SITE, POKFULAM.

In 1931-32 malaria surveys were carried out around this site. In one locality out of 125 Chinese children examined, three had enlarged spleens, a rate of 2"4 per cent. These children dwelt in huts adjacent to streams which in their lower courses flowed through cultivated and heavily manured land, and received drainage of cattle byres and pig yards of the Hongkong Dairy Farm. The upper reaches were steeply graded and in such larvae of A. minimus were seldom met with in appreciable numbers. Practically no larvae other than those of A. maculatus were collected from these streams in several searches. In the case of the other streams in the same survey the ground through which they flowed was not cultivated, no cattle byres nor pig yards drained into them nor were in their neighbourhood ; 19 children out of 26 who lived on their banks had enlarged spleens, a rate of 75 per cent. Comparatively large numbers of A. minimus larvae were found in certain portions of these streams after the rains, but during the rains only larvae of A. maculatus were found in them. In general, larvae of A. minimus were much less frequently met with than those of A. maculatus and were mainly collected from those portions of streams in which the grade was fiat. SHOUSON HILL (LITTLE HONGKONG).

Catching operations were commenced at the end of January, 1932, in a group of huts inhabited by market gardeners. The huts were constructed of bamboo and thatch and proved to be more suitable for the purpose than the village houses in Little Hongkong. As few specimens of A. maculatus were forthcoming, although its larvae abounded in the streams, day catching was supplemented by night catching at two centres from May onwards, making use of human baits. Altogether 3,368 anophelines were captured. Of these the percentages were A. minimus, 88; A. maculatus, 2 ; A. hyrcanus, 1;

A. jeyporiensis, 9. The infection rate of A. minimus was 5.63 per cent. out of 2,578 dissected, that of A. jeyporiensis 5-05 per cent. out of 277 dissected. Few A.jeyporiensis were captured during the rainy months (May to October) but in October the catch rose considerably. Its larvae had not been found to any extent in hill streams or irrigation channels. On visiting the locality in November, a large flooded ricefield lying along a hill foot was examined. The crop had been lately harvested ; 1,029 larvae were collected mainly from water in the stubble; 75 per cent. were found to be A. jeyporiensis, 25 per cent.

A. hyrcanus.

R. B. JACKSON

93

Two crops of rice are grown yearly in the Colony, the first is planted out in mid April and reaped mid July. After reaping, the stubble is ploughed in and the second crop planted. By the end of October the water is slowly drained off and the crop cut about mid November. There were no cattle at Shouson Hill but many pigs. The pigsties were fairly well lighted and ventilated which made them unsuitable as daytime resting places for anophelines. The possibilities of night catching were, however, kept in view. Both Pokfulam and Shouson Hill are situated on the island. SHING MUN CAMP. The camp was situated in the New Territory about 500 feet above sealevel in open hilly country of granite formation, the ground sloping southwards from Tai Mo Shan, a mountain 3,000 feet high. it housed the labourers who were engaged in the construction of the Jubilee or Gorge Dam across the Shing Mun river, the site being 660 yards from the camp. The work lasted from the beginning of 1933 until the early part of 1937, a period of more than 4 years. There were no habitations in the upper reaches of the Shing Mun, the inhabitants of any hamlets having been transferred and cultivation stopped when it was decided to use its basin as a catchment area for a water supply. Terraced derelict fields formerly in rice cultivationwere a feature of the stream and its tributaries from the dam site upwards. The chief anopheline breeding places were hill streams, irrigation ditches, rice cultivation and flooded fallow fields. By the end of 1933 antilarval measures were in force within a circle of half a mile radius from the camp. The engineering, medical and antimalaria staff, as well as a small police force, were housed in screened buildings. A hospital for 18 beds was also screened. The results were satisfactory after primary defects had been reported and remedied. Mosquito catching in the coolie lines being considered a most important antimalaria measure, as far as possible daily searches were made each morning by trained workers who went over each building from end to end with electric torches. The catch was subsequently sent to the Malaria Bureau for identification and dissection. A gang of coolies engaged in oiling and maintenance worked directly under the residential antimalaria staff. Checking catches in the lines, and larval surveys in the streams in order to check the oiling, were done from time to time by the staff of the Malaria Bureau. The clearing of the streams of boulders and their canalization where practicable was carried out by labour supplied by the engineering staff, who also constructed permanent antimalarial works in the. neighbourhood of the camp and European residences.

94

ANOPHELINES OF HONGKONG

With the advent of the rains in 1933 large numbers of A. jeyporiensis were caught in the lines ; it will be remembered that at Shouson Hill the catch of A. jeyporiensis in the rainy season was insignificant. Searches were made in the derelict ricefields in the Shing Mun basin : these had already been inspected at the end of the dry season, some then held stagnant water from which larvae of A. hyrcanus were collected. The majority now were flooded and larva of A. jeyporiensis were found in abundance. The flooding was caused by the dilapidated condition of the irrigation ditches: their clearing and restoration drained the fields and abolished the breeding places. At first the labourers were housed in structures of bamboo and thatch, as these were being replaced by permanent buildings, screening of the lines was asked for. This was commenced in September. Hitherto few specimens of either A. maculatus or of A. hyrcanus had been obtained in catching operations, but as a resulc of the screening they were obtained in good numbers and interesting information thereby obtained. The A. maculatus and A. hyrcanus were captured on the window gauze as if trying to escape when daylight appeared, whereas A. minimus and A. jeyporiensis were taken in dark corners or whilst resting upon clothing. During the rainy seasons in 1934-35 rieefields outside the Shing Mun basin, which had been allowed to go out of cultivation, were trained ; in 1936 there were no such within { mile of the camp. In 1934-35-36 it was noted that the catches of A. hyrcanus during the months of June, July, August, September, were low in comparison with those of other months. Searches made in rice cultivation in September yielded poor results, only a few larvae of A. hyrcanus were found, but from the middle of October onwards larvae were more numerous, those of A. hyrcanus being in the majority. As for A. jeyporiensis, the results varied not only from rice field to ricefield, but at different times in the same field. On 2nd November, 1934, A. jeyporiensis formed 2 per cent. of a collection of 200 larvae. At the end of October, 1935, it formed 25 per cent. of a collection of 317 from the same field. On 6th November, 1934, A. jeyporiensis formed 40 per cent. of a collection of 519 from a different field, but when this was searched at the end of October, 1935, 11 per cent. of 327 larvae were ./I. jeyporiensis. A. minimus was also met with in collections from ricefields ; in one made on 25th to 26th October, 1933, 763 larvae were obtained. The percentages were A. hyrcanus, 70; A. minimus, 18; A. jeyporiensis, 12. As at Shouson Hill, there was a marked rise in the A. jeyporiensis catch in October and November; this was specially evident during 1936 when there were no fallow flooded fields in the vicinity. During the year 2,589 were captured, 1,101 were taken in October, 813 in November, 202 in December. The catches and dissections for 1933-34, and totals for endemic years 1934-35-36, are given in Table I.

R. B. JACKSON

95

During 1935 the species A. fluviatilis had been recognized and the identification confirmed by the late Dr. F. W. EDWARDS, British Museum. They have been included in the A. minimus figures for 1936. WOO LI HOP.

Mosquito catching was done by the staff of the Bureau during every month except May in 1933, on 40 mornings. The village was half a mile from the camp and north-west of it, consisting TABLE I.

Locality and year.

Shing M u n 1933

Number of morning catches. 239

Dissections : Malaria Bureau staff.

Midgut infection.

Total infections.

Percentage of infections.

1

153 717 8 27 0 0

269 1,086 8 34 0 0

12.48 9.93 3.48 1.21 0.00 0-00

Species.

Number caught.

Number dissected.

A. A. A. A. A. A.

mlnimus jeyporiensis maculatus hyreanus splendidus karwari

4,644 25,317 277 3,144 26 1

2,155 10,936 230 2,818 25

Gland infections.

11 36

Woo Li Hop 1933

40

A. A. A. A. A.

minimus jeyporiensis maculatus hyrcanus splendidus

1,316 4,041 194 197 4

1,185 3,707 187 176 4

18 80 0 0 0

43 119 0 0 0

3'63 3"31 0"00 0"00 0"00

Shing M u n 1934

355

A. A. A. A. A. A.

minimus jeyporiensis maculatus hyrcanus splendidus karwari

1,033 5,482 1,055 6,9O9 50 4

775 4,166 900 5,245 48 4

14 83 8

23 149 10

14

14

2.97 3'58 1.11 0-27 4.17 0.00

A. A. A. A. A.

minimus jeyporiensis maculatus hyrcanus splendidus

577 1,242 6O2 152 5

465 991 476 127 5

3 0

9 17

3

3

0 0

0 0

1-72 0.63 0"00 O.00

A.

minimus

3,046 10,845 3,444 19,792 125 45

2,584 8,906 3,191 16,421 116 42

6 1 5 7 8 2 0

90 330 23 55 2 0

3.48 3"70 0.72 0'33 1"72 O'00

Woo Li Hop 1934"

Shing Min Totals 1934, '35, '36

91

1,054

,4. jeyporiensis A. maculatus A. hyrcanus A. splendidus A. karwari

2

o

2

i

o

1.94

96

A N O P H E L I N E S OF H O N G K O N G

of some 26 single-storied buildings built of stone and roofed with tiles ; population approximately 126. Cattle, pigs and dogs were kept, in some instances cows were housed under the same roof as their owners, in other cases cows and pigs were separated only by a wall from the villagers. There was a considerable amount of pineapple cultivation in the neighbourhood. The great majority of the anophelines were captured in the dark, ill-ventilated byres and pigsties with the help of electric torches. The numbers of A. macudatus and A. hyrcanus were small in comparison with those of A. minimus and A. jeyporiensis owing to the greater tendency of the latter to remain in the buildings after feeding. In 1934, 91 morning catches were made. The results and dissections for both years are shown along with Shing Mun catches and dissections for comparison in Table I.

Precipitin Reactions. Dr. C. TOUMANOFF,of the Pasteur Institut Indo-China, visited the Colony in 1934 whilst engaged in collecting material for his work L'Anoph~lisme en Extreme-Orient, Masson et Cie, Paris, 1936. Previous to his visit little work had been done in Hongkong with regard to precipitin tests for the determination of sources of anopheline blood meals. A few specimens of blood from gorged A. maculatus obtained from goat pens had been tested against anti-human sera with negative results. At his request blood taken from the midguts of anophelines caught in various places were forwarded to him. Certain of his results translated from the French are given in Tables II and III. In both 1933 and 1934 there was a marked difference between the infection rates of mosquitoes taken at Shing Mun and those caught at Woo Li Hop (Table I). In both places there was the same anopheline fauna. The population of Shing Mun was composed of Cantonese and a considerable number of labourers from Shanghai ; it fluctuated from month to month. In the tropics there would be usually no scarcity of malaria carriers in such an assembly. The population of Woo Li Hop was a settled one. At Shing Mun the animals were represented by a few goats belonging to the Indian Police and some dogs owned by Europeans. At Woo Li Hop cattle, pigs and dogs lived side by side with their owners. As shown in Table II, the anophelines fed mainly on man at Shing Mun, on animals at Woo Li Hop. Reduction of the rates in both cases in 1934 may be ascribed to reduction of breeding places, especially those of A. jeyporiensis by antimalaria work, which work also abolished the epidemic malaria at the camp. Table I gives the totals of the morning catches and dissections for the endemic years 1934-35-36. In the Colony, A. maculatus has only been found infected at the camp and at Woo Li Hop. At this village a fair number were captured in 1934 and three infections found ; these may have been contracted at the camp. On the other hand, it was not impossible for them to have been

R. B. JACKsoN TABLE I I .

97

Precipitin tests by Dr. C. TOUMANOFF.

SHING M U N .

Species.

A. hyrca~tu$ A. jeyporiensis

Number examined.

Number positive.

137 76

117

Anti-sera. Cattle.

Man.

Pig.

113

60

58

A. maculatus

42

41

39

A. splendidus A. minimus

2 21

1

10

1 10

278

229

221

ixed

Dog.

--

3

--

1

--

4

-

-

-

-

I

--

Observations.

1(1)

i 1(1) i

1 with antigoat s e r u m 2 with antigoat s e r u m

2

3 reactions with antigoat s e r u m

m

W o o LI HoP.

A. A. A. A.

hyrcanus jeyporiensis maculatus minimus

--

7

8 77

93

130

I

127

264

1

43 I I

2 48

I

I

3

~3 ' 1 117

I

5

189

1

1

(1) 1 (1) 2 (1)

1

5

i

1I -

8

i I

SHEUNG K W A I CHUNG,

A. A. A. A.

]?yrcQnu$ jeyporiensis maculatus minimus

29 1 28 78

130

28 1 28 72

---12

28 1 28 58

. -.

I

1

. -.

. . 1

-7---?--

. . ---

--

1 (1)

--S--:-

T h e figures placed in the m i x e d reaction c o l u m n s b e t w e e n parentheses and b y the side of the n u m b e r of ceactions indicate the mixed reactions comprising h u m a n blood.

acquired at Woo Li Hop, for a minority of A. maculatus had been found to feed upon human beings there (Table H). Also A. maculatus had been readily infected with subtertian malaria (14 out of 22 which fed) at the Malaria Bureau in 1935. It was not found infected in 306 dissections done during the period 1932-37, of those caught in huts at Shouson Hill, a malarious district. Neither

98

ANOPHELINES OF HONGKONG

was it found infected in 2,395 specimens obtained by night catching in Pokfulam cattle byres, nor in 1,311 dissections of those caught in night catches in Shouson Hill pigsties. In addition, salivary glands of 843 from Pokfulam whose midguts had been used in precipitin tests were examined with negative results. The majority of these dissections were done during the malarious season. Its infection rate was low as compared with either A. minimus or A. jeyporiensfs in the camp dissections, but whereas there was a possibility of these two species arriving already infected at the camp from outside the sanitated area, there was much less likelihood of this happening in the case of d. maculatus owing to its partiality for animal blood when available. The infection rate of A. hyrcanus was much lower than that of d. maculatus. In 1935 a batch of three A. minimus, four A. maculatus, seven A. hyrcanus, TABLE I I I .

Precipitin tests by D r . C . TOUMANOFF.

SHOUSON HILL.

Species.

Number examined.

Anti-sera.

Number positive.

l.

Cattle.

Man.

A. A. A. A.

hyrcanus I maculatus jeyporiensis minimus

20 10

20 10

1

1

1

182

141

263

213

143

.

Pig.

Observations.

.

Dog.

Horse.

19 10

1

232

.

--

33

4

4 (4)

62

4

4

/

SHEK O (Cattle byres).

A. A. A. A.

hyrcanus jeypo~iensis mac ulatus min[mus

237 43 48

230 2 42 46

330

320

2

1

1

227 1 41 45

3 -1

314

4

1 (U 1

POKFULA~ (Cattle byres).

A, h~canus A. maculatus

i

617 618

T h e figures placed in t h e m i x e d reaction c o l u m n s b e t w e e n p a r e n t h e s e s a n d b y t h e side of t h e n u m b e r of reactions indicate t h e m i x e d reactions c o m p r i s i n g h u m a n blood.

R. B. JACKSON

99

were fed upon the same patient, at the same time, under the same conditions, at the Malaria Bureau. One A. minimus, two A . maculatus became infected, but none of the seven A. hyrcanus. The blood of the patient who was not then suffering from fever contained numerous crescents. The pigment in the zygotes met with in dissections of A. hyrcanus was almost always of the nature ascribed to benign tertian infection, namely, fine yellow grains arranged in wisps. The failure to infect A. hyrcanus with subtertian malaria and its partiality for animal blood seems to account for its low infection rate. It was found naturally infected once in 171 dissections of those taken in the Shouson Hill huts, infections were also found in specimens captured in " mosquito p r o o f " coolie lines in a sanitated area at Patheung aerodrome along with infected specimens of A. minimus and of A. jeyporiensis. The A. hyrcanus infection rate was low but the catches were large. In the Shing Mun dissections salivary gland infections were found in every month of the year, but were uncommon in the early months. The infection rates were low in the first quarter, rose during the second, remained high during the third, and in the fourth quarte r declined towards the end of the year. NIGHT CATCHING OF ANOPHELINES.

Pokfulam Cattle Byres. By permission of the manager of the Hongkong Dairy Farm, this was begun in 1935 in two byres situated in the locality where a low spleen rate had been obtained in the Queen Mary Hospital site survey, as already mentioned. The catching was done by cattle men after preliminary instruction. They caught for 1½ hours after dark : 9,812 anophelines were obtained, either feeding upon the cattle or resting when gorged on the walls of the byres. The details are as follow: A. A. A. A. A. A.

maculatus

hyrcanus

minimus

jeyporiensis

splendidus

va~s

9,619 88 56 17 1 31 Dissections of a large number of A. maculatus captured have already been referred to. Reference to Table [II indicates that this species was feeding on the cattle.

Shouson Hill Pigsties. Night catching by pig attendants was started about the same time as above in two pigsties. One sty was situated in A. maculatus country, the other in A. hyrcanus country : 4,272 anophelines were captured. A. A. A. A. A. A.

macu!atus 2,036

hyrcanus 1,811

minimus 220

jeyporiensis 103

tessellatus 101

karwari 1

100

ANOPHELINES OF HONGKONG

As Dr. TOUMANOFF had gone on home leave in 1935, Dr. GREAVES, the Government bacteriologist, was good enough to arrange for the preparation and supply of anti-sera for the use of the Malaria Bureau. Sheung Kwai Chung was a Chinese village ~ a mile from the camp and west of it. Material for precipitin tests was obtained from it and submitted for examination. The results are given in Table II. As there were few reactions to anti-pig sera in the material from Woo Li Hop or Sheung Kwai Cheung where cattle were present ; the results of Shouson Hill tests where cattle were absent are given in Table IV. The reactions indicate that A. maculatus and A. hyrcanus feed upon pigs in the absence of cattle ; dissections show that they were of little importance there as regards the transmission of malaria. The material for Dr. TOUMANOFF'SShouson Hill tests was obtained from mosquitoes taken in day and night catches in human habitations. Results obtained from anophelines caught in a goat pen at Shing M u n indicate that goats were acceptable as a blood meal. No infections were found in the salivary glands of the mosquitoes used in this precipitin test. As few A. hyrcanus were available in the figures for Woo Li Hop or Sheung Kwai Cheung, results from Shek O are given. Cattle were not usually kept in Chinese villages on the island ; the mosquitoes were captured in a byre made of bamboo and thatch situated on the outskirts of the village. FILARIA.

From time to time larval filariae were encountered in the thorax, neck and head of anophelines undergoing dissection. Several specimens were found infected with both malaria and filariae. Microfilariae were met with in thick blood films made from persons living in the dwellings where the mosquitoes had been captured. The larval filariae corresponded to the description given of the various stages of Wuchereria bancrofti. Of 18 A. hyrcanus, 10 A. minimus, 11 A. maculatus which had been fed once upon a patient whose blood contained microfilariae (W. bancrofti) 14, four and four, respectively, became infected. Proboscis infections were met with in A. hyrcanus and A. maculatus. In the case of A. minimus infections were found in the head. No A. jeyporiensis were available at the time of feeding. Annual inquiries were made at Government hospitals. Few diseases caused by filaria infection were reported.

SUMMARY. (1) Flooded fallow ricefields at Shing Mun were a fruitful source of A. jeyporiensis var candidiensis and A. hyrcanus vat sinensis. Rice cultivation when the second crop was ripening was another source at Shouson Hill and Shing Mun, both were situated in hilly localities.

R. B. JACKSON TABLE IV.

101

R e s u l t s of preeipitin tests : Staff of Malaria Bureau.

S~IOUSON HILL (Pigsties).

Species.

Number examined.

Anti-sera. Number

positive.

Observations. Man.

Cattle.

Pig.

A. hyrcanus

85

83

81

A. A. A. A.

46 5 4 15

44 2 14

m

44 2 2 14

155

145

--

maculatus jeyporiensis minimus tessellatus

2

Dog.

Goat.

Mixed. 2

M a n & pig 1 D o g & pig 1

m

143 i

SHING MUN ( G o a t pens).

A. A. A. A.

hyrcanus jeyporiensis maculatus minimus

8 8 28 4

27 4

8 8 27 4

48

47

47

8 8

(2) Precipitin reactions indicated the marked partiality of A. maculatus and A. hyrcanus var sinensis for the blood of cattle, pig, goat ; in their presence dissections indicated that these two species were of little or no significance in the transmission of malaria. In the absence or scarcity of suitable animals as at Shing Mun, they fed upon man and became infected with malaria. Their infection rates were much lower than those of A. minimus or of A. jeyporiensis. Reasons have been suggested to account for these. (3) A. minimus and A. jeyporiensis var candidiensis were the important malaria carriers in the Colony. (4) The four common anophelines were efficient intermediate hosts of W. bancrofti.