Resurgence of Anopheles sacharovi following malaria eradication

Bull. Org. mownd Santd 1973, 48, 699-703 Bull. Wid Hithu Org.f Resurgence of Anopheles sacharovi following malaria eradication J. HADJINICOLAOU 1 & B. BETZIOS 2 In the Lamia Plain, Greece, 12 years after the cessation ofDDT spraying, Anopheles sacharovi is still present in very high densities and appears to have the same biting habits and host preferences as previously. Mosquitos of this species are still resistant to DDT and dieldrin. Intensive indoor spraying of DDT and other resi- dual insecticides was discontinued in Greece almost 12 years ago and malaria, although not eradicated sensu stricto, is no longer considered to be a public health problem of any importance. According to the latest information from the Ministry of Social Services (D. Avramides, personal communication) 26 malaria cases were detected in the whole of Greece during the 1970 transmission season, 8 of them being classified as indigenous (6 of these were concentrated in one particular area, 51 km west of Salonica), I as a relapsing case, 8 as induced, and 9 as imported cases. The dramatic effect of indoor residual spraying on domestic anopheline populations (particularly Anopheles sacharovi, the principal malaria vector in Greece) is well known. An obvious change in the behaviour of this species, at least as regards its resting habits, was noted from the onset of spraying operations and this change has been inter- preted in different ways (Hadjinicolaou, 1954). Not very long after the initial application of residual insecticides, the phenomenon of resistance of A. sacharovi to DDT and dieldrin was observed and confirmed, at first in the District of Laconia (S. Peloponessus) and later in several other districts. In routine field surveys it has been found that the densities of A. sacharovi are now as high as ever in most areas where it was known to breed profusely before DDT was used. This mosquito is now being found in abundance in houses, stables, and animal sheds and is biting man freely indoors and in the 1 Head, Laboratory of Insects of Public Health Impor- tance, Benaki Phytopathological Institute, Athens, Greece. ' Assistant, Laboratory of Insects of Public Health Im- portance, Benaki Phytopathological Institute, Athens, Greece. open. Since extensive data are available on the biology of A. sacharovi and its behaviour in Greece prior to the introduction of DDT, it was thought that it would be of some value to investigate the present density, biting habits, and host preferences of this mosquito. The investigations began late in the 1968 season and continued through the 1969 and 1970 seasons. THE LOCALITY Lamia plain, situated 190-250 km north-west of Athens, was formerly an area with a high degree of malaria endemicity; the malaria vectors A. sacha- rovi, A. superpictus, and A. maculipennis and the nonvector rural species A. hyrcanus, A. claviger, A. algeriensis, A. plumbeus, and A. marteri were all well represented (Livadas-Sphangos, 1940). The area of the plain is estimated to be about 400 km2. The river Sperchios flows through it and its estuary is about 4 km from the village of Thermopylae. The population, according to the March 1971 census, is 160 000 but this figure includes the in- habitants of the mountainous Phthiotis District. This area is mainly agricultural and the livestock is composed mainly of sheep and goats, although a considerable number of dairy cattle and other domestic animals are kept in certain areas of the plain. The Lamia plain was subjected to intensive DDT treatment from 1946 to 1959. Since then, no residual insecticide of any kind has been used as an anti- malarial measure. The small village of Thermopylae is situated on the main highway at a distance of 2 km from the Thermopylae sulfur springs, 20 km south-east of 3068 -699- J. HADJINICOLAOU & B. BETZIOS Lamia and 15 km north-west of Kamena Vourla on the sea shore. In the village there are 75 houses, 70 stables, 40 warehouses, and 9 animal sheds. There are 350 inhabitants, but during July, August, and September the population increases considerably as visitors come to stay in the village. The animal population of the village consists of about 85 cows, 75 horses, mules, and donkeys, and 3100 sheep and goats. There are also a few pigs and a number of chickens, rabbits, cats, and dogs. Most of the houses of the village are protected by wire screening, but the main doors are usually not screened; the screening in some houses is badly maintained. Many of the inhabitants use aerosol sprays in their bedrooms. During the hottest period of the summer (July-August) a few people may sleep under bednets in the open. A field laboratory was established in one of the typical village houses and entomological observations were carried out there from August 1968 until the end of the 1970 season. RESULTS Throughout the period of this investigation hand- catching of mosquitos was practised regularly in and around the observation village. Periodic catches were made from human habitations, stables, sheep sheds, artificial pit shelters, and also from our field station during the course of observations of the nocturnal activities and the behaviour of anophelines in the presence of the insecticide. A considerable proportion of the catch was classified according to species and the results are given in Table 1. A. sacharovi appeared to be the main malaria- vector species in all types of catch and shelter. A. superpictus and A. maculipennis were present only in small numbers. Of the nonvector species, only A. hyrcanus was observed biting indoors and out- doors, in addition to A. sacharovi. Before DDT was used, A. sacharovi was the pre- dominant species in the lower part of the Lamia plain, but A. superpictus and A. maculipennis were then represented in considerably higher proportions, ranging from 4% to 17% of the total catches of anopheline malaria vectors for A. superpictus, and from 1 % to 8% for A. maculipennis (Sphangos, 1943). Since the Second World War a lot of drainage work has been done in the plain, particularly in the freshwater marshy areas, and thousands of hectares have been reclaimed for agriculture. This has led to the virtual disappearance of A. maculi- co (I, ._ (D ._ 0 0 a ._ 0 0 co 0 CD 0 .U 0 co 0i I- C C .0 0 (D, CD CL 0 .0 0 0 r-V..a) C) CD 0CDco CD 0 co 0 0 ,x0 cU 0i cL tC C.)ftt coO Cbl0 co-0 C eco co0 sx 0o-0 0 0 0 0 0 w-0 0 -0 0e0-COe -0 6 c.* M* LOcono.- o ID 0Dt 00 cO)m r..o a 0 Lar 0n (NO)6 0, 0 co D 0 co LO N - Lo N 0 10 I, * NO I le X CDV. 0* I N Dr. I 0 0 o o 0 r- 0 I.-C.) 0 LO ,L (NO C0OO 0, SD b (N 0 co co 0 6e 0 ae 1vC.Ico 0 NO) -Lat 0i V. C 0 o I O NN r, * e * 80 O _-m u V.- co (N 0 1 N0 * ..J*0e ae (v,0 _-0 (N 0 XN.I ovo- (.)* 0,* -* oo co ax m r oo P, Ps -O ma _w I LO CD 0 0 _- _- C4N co 0 (N (D U)a0 0)o. o n ° 0 0 .C W WujzD W >e _C o E-,E C.no E'O* 700 atL _O 1-0 0 0 C4 U w c6 N C r-0, _ 0 00( 00 co r (VN 00 O) -0E CNO(N_ _~r _. CO ( 0, CO 0. I I RESURGENCE OF ANOPHELES SACHAROVI FOLLOWING MALARIA ERADICATION Fig. 1. Cycle mosquitos.a of nocturnal activity of anopheline a Numbers of mosquitos entering a baited bedroom on 5 different nights: Thermopylae, 1968. pennis from the area. In addition, a stream that flowed from the hills, through the plain, to the sea has been diverted for irrigation purposes, and no other suitable breeding places exist for A. superpictus elsewhere in that part of the plain. The high proportion of A. sacharovi in the total catches at the Thermopylae field station are reflected in the data given in Table 1. The proportion of A. hyrcanus caught during the night was higher than the proportion during the day from human habi- tations, stables and pit shelters, indicating that this species may enter a room at night, feed, rest for some time, then leave at dawn to shelter elsewhere (Table 1). The cycle of nocturnal activity of ano- pheline mosquitos is shown in Fig. 1. Host preferences as determined by precipitin tests With the object of obtaining information on the present-day host preferences of A. sacharovi, and of comparing these with the data available from the pre-DDT days, a number of blood-meal smears were collected from mosquitos in human habitations, stables, and artificial pit shelters in the 1968 and 1970 seasons in the village of Thermopylae. The smears were tested at the Imperial College of Science and Technology in London, England, and the results are tabulated in Table 2. Table 2. Results of precipitin tests of A. sacharovi blood meals from Thermopylae 1968 1970 Host Human Animal Artificial Human Animal sheds Artificial pit shelters habitations sheds pit shelters habitations Si a S2a Total Pi a p2a Total man 187 3 9 100 1 4 5 0 1 1 (61.5 %) (1.3 %) (5.1 %) (38.5 %) (0.3 %) (1.1 %) (0.7 %) (2.2 %) (1.8 %) animal 114 232 164 136 309 320 629 10 42 52 (37.5 %) (98.3 %) (93.7 %) (52.3 %) (93.1 %) (84.9 %) (88.7 %) (100.0 %) (93.3 %) (94.5 %) mammal 1 0 0 1 1 4 5 0 1 1 (0.3%) (0.4%) (0.3%) (1.1 %) (0.7%) (2.2%) (1.8%) mixed feeds 2 0 0 10 1 3 4 0 0 0 (man + animal) (0.7 %) (3.8 %) (0.3 %) (0.8 %) (0.6 %) mixed feeds 0 1 1 13 19 44 63 0 0 0 (animal + animal) (0.4 %) (0.6 %) (5.0 %) (5.7 %) (11.7 %) (8.9 %) negative 0 0 1 0 1 2 3 0 1 1(0.6 %) (0.3 %) (0.5 %) (0.4 %) (2.2 %) (1.8 %) total 304 236 175 260 332 377 709 10 45 55 a SI = sheep shed in the periphery of the village S2 = stable in the village Pi = pit shelter in the periphery P2 = pit shelter in the village. 701 J. HADJINICOLAOU & B. BETZIOS Table 3. Host preferences of A. sacharovi collected from houses, stables and artificial pit shelters in 1932-34, in 1968, and in 1970 From houses From stables From artificial pit shelters Anopheline species Year Locality Total Man Animal Total Man Animal Total Man Animal positive positives positives positive positives positives positive positives positives reactions (%) (%) reactions (%) (%) reactions (%) (%) A. sacharovi 1932-34 Kavalla, 3 980 61.3 38.7 2 855 7.5 92.5 - - - Macedonia a A. sacharovi 1968 Lamia 304 61.5 38.5 236 1.3 98.7 175 5.1 94.9 A. sacharovi 1970 Lamia 260 38.5 61.5 709 0.7 99.3 55 1.8 98.2 a Data from Barber & Rice (1935) A. sacharovi has been described as an anthropo- philic species in Greece (Lividas & Sphangos, 1941). The term may not be strictly appropriate, but the species is indeed anthropophilic in the sense that it bites man to a high degree in the presence of large numbers of animals. The results of precipitin tests of samples in 1968 from Thermopylae show that roughly 61 % of the mosquitos from human habita- tions had fed on man, a very high proportion con- sidering that the man-animal ratio of that village was about 1: 9, or 1: 7.2 at the peak of the summer season. Table 3 presents the results of a large number of precipitin tests of A. sacharovi blood smears of speci- mens collected from houses and stables in the Kavalla area during 1932-34 (Barber & Rice, 1935). If the degree of anthropophily of this species at that time is compared with that in 1968 in the Lamia plain (included in the same table) it will be noted that there is hardly any difference. The results of 1970, how- ever, present a somewhat different picture. Genetic status of A. sacharovi populations In September 1968, a few individual egg batches of A. sacharovi taken from specimens collected separately from bedrooms and artificial pit shelters at Thermopylae were sent to the Ross Institute so that they might be crossed with colonies of A. sacha- rovi from other sources or countries. Dr G. Davidson (personal communication) reported that the material sent from Lamia was found to be the same species as the Turkey strain of A. sacharovi maintained at the Institute. Four families from artificial pit shelters and 5 families from bedrooms were found to be conspecific. In Turkey, and more specifically in Turkish Thrace on the other side of the river Evros, A. sacharovi is found in large numbers and a considerable num- ber of malaria cases have been recorded in recent years (C. Ramsdale, personal communication). Hence the danger of malaria gaining a foothold on the Greek side of the river should not be underesti- mated. In many formerly malarious countries, where the disease is no longer considered a major public health problem, there is a tendency to ignore or to minimize the potential danger ofmalaria reappearing and, under favourable circumstances, leading to local or widespread outbreaks. In Greece, A. sacharovi exists in very high densities and the species appears to have the same habits as in the days before DDT was used. It is highly anthropophilic, as it always has been, and certainly there is no reason to think that its potentiality as a vector is now lower than that it has been in the past. Susceptibility tests A. sacharovi in Greece has been for a number of years resista tont both DDT and dieldrin. This has been reconfirmed by susceptibility tests carried out at Thermopylae in August-eptember 1969. The mor- tality after exposure to 4% DDT for 1 h was 33.8%, and after similar exposure to 4% dieldrin was 5.6%. ACKNOWLEDGEMENTS The writers thank Dr D. Avramides, Head of the Malaria Section of the Ministry of Social Services, for his interest and encouragement, and Dr N. Kyrikos, Director of the Lamia Health Centre, for seconding Mr C. Sianos, Sanitary Inspector, to help with the field investigations. They also acknowledge with thanks the assistance given by Mr G. Bekios of the Lamia Malaria Experimental Station. 702 RESURGENCE OF ANOPHELES SACHAROVI FOLLOWING MALARIA ERADICATION 703 RtSUM1 REAPPARITION D'ANOPHELES SACHAROVI APRES tRADICATION DU PALUDISME Une etude a ete entreprise dans la plaine de Lamia (Grece) sur le comportement actuel d'Anopheles sacharovi apres plusieurs anne'es d'interruption des pulverisations de DDT, le paludisme ayant et6 completement elimin6 de cette region. A. sacharovi semble etre 'a 'heure actuelle le seul vecteur du paludisme rencontre dans la partie basse de la plaine qui s'6tend vers la mer. Sa densit6 est elevee, comme le montrent les recoltes effectuees dans les habi- tations, les etables et les fosses-abris naturelles ou artifi- cielles. Les moustiques appartenant a cette esp&ce piquent spontanement 1'homme tant a 1'ext6rieur qu'a l'interieur des habitations ou ils penetrent en grand nombre, et constituent maintenant un veritable fleau aux alentours du village des Thermopyles. A. sacharovi ne semble pas avoir change ses habitudes depuis l'epoque oui le traitement au DDT n'existait pas encore. Ses hotes prefer6s sont les memes que dans les annees 30. L'esp6ce est hautement anthropophile, c'est- a-dire que, meme en presence d'un grand nombre d'ani- maux, elle est attiree par l'homme. De plus, elle est r6sistante au DDT et 'a la dieldrine. D'apres des renseignements fournis par le Ross Institute of Tropical Hygiene de Londres, A. sacharovi rencontr6 dans la plaine de Lamia est bien la meme espece que A. sacharovi que l'on trouve en Syrie et dans certaines regions de Turquie. REFERENCES Barber, M. A. & Rice, J. B. (1935) Ann. trop. Med. Parasit., 29, 3 Hadjinicolaou, J. (1954) Observations on the control of some insects of medical importance. In: Proceedings of the First International Symposium on the Control of Insect Vectors of Disease, Rome, 1953, pp. 160-183 Livadas, G. A. & Sphangos, J. C. (1941) Malaria in Greece Athens, Pyrsos Press, vol. 1, pp. 69-107 Sphangos, J. C. (1943) The use of Gambusia in malaria control in Greece. Thesis, Akadimaiki latriki, Athens