Using seven methods of surveillance, 58 species of mosquitoes from nine genera were in Pantai and the two neighbouring villages during two visits in 1982. Ma. bonneae was the most prevalent species attracted to man. In the forest shade Ma. bonneae and Ma. dives showed activity throughout the 24 hours with peak biting during 1900-2100 hours. An. balabacensis exhibited peak activity shortly after midnight. Inside and outside house, Ma. bonneae showed similar activity except that it ceased during the day. Mansonia was only mildly zoophilic. CDC light traps gave poor yields of mosquitoes. Pyrethrum spray catch inside houses early morning did not include any Mansonia. Outdoor day resting catch included Ma. bonneae fed on man. Transmission of Brugia, probably human filariasis, by Ma. bonneae occurred in Pantai and in the two neighbouring villages. One infection in Ma. dives was found in Pantai. The monthly infective biting rate and monthly transmission potential for Ma. bonneae were estimated at the forest shade and outside the house in Pantai.
Studies on age groups within activity cycles, age composition and survivorship in natural populations of Mansonia in Kampung Pantai, Bengkoka Peninsula of Sabah state have been described. Early activity of 3-5 parous Ma. bonneae during the first hour after sunset was noted. Age composition of Ma. bonneae at forest shade, indoor and outdoor of house, comparative buffalo vs human bait outdoor in Kampung Pantai showed all round high parous rates ranging from 66.7 to 75.4%. Population 3-parous and older ranged from 18.8 to 26.7%. Nine of the 14 infective Ma. bonneae were 3-parous and this segment of the population was engaged in active transmission. High parous rates were observed in Ma. dives and Ma. uniformis taken in small numbers. Parous rates of Ma. bonneae taken in Kampung Delima and Kampung Taradas were also high. Estimates of daily survivorship of Ma. bonneae and Ma. dives determined by two methods were very high.
Brugia malayi and Wuchereria bancrofti infections cause lymphatic filariasis in Malaysia. About 2.5 million people live in endemic areas of filariasis, of whom 5% have microfilaraemia and probably twice as many are infected. There is a wide clinical spectrum of response to the infection. While some have asymptomatic microfilaraemia, others have episodic attacks of fever, lymphadenitis, retrograde lymphangitis and lymphoedema. Elephantiasis is a late complication. Tropical pulmonary eosinophilia and other forms of occult filariasis are due to hyper allergic reactions to microfilarial antigens. Parasitological and serological tests aid in confirming the clinical diagnosis. The drug of choice is diethylcarbamazine citrate.
The filaria vector competence of Anopheles stephensi was compared with Brugia-susceptible Aedes aegypti Liverpool strain, An. gambiae Badagry Lagos strain and An. dirus Perlis Malaysia strain. An. stephensi ingested more Brugia pahangi microfilariae, had the highest infectivity rate and yielded more infective mosquitoes than the other two anopheline species. The overall vector competence of An. stephensi was 0.13 times that of Ae. aegypti, 0.62 times that of An. gambiae and 2.17 times that of An. dirus. However, heavy mortality among infected An. stephensi in the present investigation indicates that the filaria vectorial capacity of the mosquito might be limited epidemiologically. The relationship between filaria vector competence and mosquito foregut armature is discussed. It was observed that the relative vector competence of the three anopheline species tested was in the same order as their relative degrees of armature elaboration. The converse would be expected if foregut armatures really give partial protection to the mosquitoes against filarial infection. It is suggested that high host microfilariae density favours larval survival proportional to the degree of armature development in Anopheles (Cellia) species.
We conducted a field study of a rapid test (Brugia Rapid) for detection of Brugia malayi infection to validate its sensitivity and specificity under operational conditions. Seven districts in the state of Sarawak, Malaysia, which are endemic for brugian filariasis, were used to determine the test sensitivity. Determination of specificity was performed in another state in Malaysia (Bachok, Kelantan) which is non-endemic for filariasis but endemic for soil-transmitted helminths. In Sarawak both the rapid test and thick blood smear preparation were performed in the field. The rapid test was interpreted on site, whereas blood smears were taken to the district health centres for staining and microscopic examination. Sensitivity of Brugia Rapid dipstick as compared with microscopy of thick blood smears was 87% (20/23; 95% CI: 66.4-97.2) whereas the specificity was 100% (512/512). The lower sensitivity of the test in the field than in laboratory evaluations (> or =95%), was probably due to the small number of microfilaraemic individuals, in addition to difficulties in performing the test in remote villages by field personnel. The overall prevalence of brugian filariasis as determined by the dipstick is 9.4% (95% CI: 8.2-0.5) while that determined by microscopy is 0.90% (95% CI: 0.5-1.3) thus the dipstick detected about 10 times more cases than microscopy. Equal percentages of adults and children were found to be positive by the dipstick whereas microscopy showed that the number of infected children was seven times less than infected adults. The rapid dipstick test was useful as a diagnostic tool for mapping and certification phases of the lymphatic filariasis elimination programme in B. malayi-endemic areas.
Surveillance methods for Coquillettidia crassipes were studied in an open housing estate near Kuala Lumpur using three types of traps Trinidad 10 trap, modified Lard can trap and IMR trap, each baited with chicken or pigeon. All traps attracted Cq. crassipes. There was no significant difference in the catches in the three traps. There was also no significant difference between chicken and pigeon as bait. Catches at heights of 1.5, 3, 4.5 and 6 m did not show any significant difference in density. Cq. crassipes was active at night with an early peak during the first hour of the night and a minor peak between 0100 and 0200 hours. The activity of the parous and nulliparous sections of the population was similar, except that a higher proportion of the parous females was active during the second peak compared with the nulliparous females. The parous rate was 22.3%, and the probability of survival through one day for two gonotrophic cycles was 0.711 and 0.650. The infection rate for Cardiofilaria was 29 out of 1052 (2.76%) and the infective rate (L3 larvae) was 13 out of 1052 (1.24%). 48.3% of the infected Cq. crassipes had a worm burden of more than ten larvae. One of the chickens in the traps was positive for microfilariae of Cardiofilaria four weeks after exposure as bait. Laboratory bred Cq. crassipes fed on this chicken produced infective larvae in ten days, and these were inoculated into clean chickens and pigeons. Microfilariae appeared in the chickens but not in pigeons. The adult worms recovered await identification.
A preliminary field study was undertaken to evaluate the efficacy of a mosquito trap; Mosquito Killing System (MKS) in
capturing mosquitoes and other insects. MKS has an automatic activation by the use of a photocell. It is also supplemented
with carbon dioxide and heat as attractants for mosquitoes and other insects. Three units of MKS were employed at three
different locations within two study sites for ten days. The mosquitoes and other insects that were trapped in MKS were
collected and morphologically identified daily in the laboratory. A total of 1,928 mosquitoes and other insects were
trapped in all units of MKS. High numbers of mosquitoes (93.05%), particularly Aedes sp. and Culex sp. were captured
from MKS. Among these, Culex quinquefasciatus (91.81%) was most abundant species collected. Only 0.84% of Aedes
aegypti and Aedes albopictus trapped in MKS. Female mosquitoes (83.44%) were found to be more attracted to MKS
compared to male mosquitoes of various species. These findings illustrated the potency of MKS utilization in surveillance
and control activities of Cx. quinquefasciatus; a nuisance mosquito and also potential vector of urban brancroftian
filariasis in Malaysia.
We are reporting a case of an eye lesion caused by an adult Brugia malayi. The patient was a 3-year-old Chinese boy from Kemaman District, Terengganu, Peninsular Malaysia. He presented with a one week history of redness and palpebral swelling of his right eye. He claimed that he could see a worm in his right eye beneath the conjunctiva. He had no history of traveling overseas and the family kept dogs at home. He was referred from Kemaman Hospital to the eye clinic of Hospital Tengku Ampuan Afzan, Kuantan, Pahang, Malaysia. On examination by the ophthalmologist, he was found to have a subconjunctival worm in his right eye. Full blood count revealed eosinophilia (10%). Four worm fragments, each about 1 cm long were removed from his right eye under general anesthesia. A thick blood smear stained with Giemsa was positive for microfilariae of Brugia malayi. A Brugia Rapid test done was positive. He was treated with diethylcarbamazine.
Study site: Opthamolagy clinic, Hospital Tengku Ampuan Afzan
The leaf-monkeys, Presbytis cristata and Presbytis melalophos, experimentally infected with subperiodic Brugia malayi, have been used for studies on the pathoimmunology of the infection and the screening of potential filaricides during the last 6-8 years, and considerable information on the pattern of microfilaraemia and adult worm recoveries have been obtained. The prepatent periods in 97 P. cristata and 45 P. melalophos, each infected with about 200 infective larvae, were similar, these being approximately 70 and 68 days respectively. Although all infected animals became microfilaraemic, the peak geometric mean count was much higher in P. cristata than in P. melalophos, this being 182.0 and 65.8 per ml blood respectively. Mean adult worm recovery expressed as the percentage of the infective dose was 4.7% and 2.5%, respectively. Most worms were recovered from the sacral nodes/thoracic duct or inguinal lymph nodes in these animals. In view of the higher worm recovery and the higher peak microfilaraemia attained, it is concluded that P. cristata is a better model for the infection than P. melalophos.
R. sabanus and R. muelleri are very common in the lowland forests of Malaysia. In nature they are infected with Breinlia sp. and D. ramachandrani. In an attempt to determine whether they are also susceptible to subperiodic B. malayi and thereby being potential reservoirs of infection of the disease, 24 R. muelleri and 17 R. sabanus were experimentally infected with the parasite. Results show that although they can support the full development of the parasite, they are poor hosts. This confirms the observation that in Malaysia natural infection of Rattus spp. with the parasite has not been seen. These rats therefore are probably not important in the zoonotic transmission of subperiodic B. malayi in Malaysia.
Thirteen strains among 3 species of entomopathogenic bacteria were tested against 3 medically important mosquito species in French Polynesia. Two strains of Bacillus thuringiensis were highly toxic to Aedes polynesiensis, Aedes aegypti, and Culex quinquefasciatus. Six of 7 strains of Bacillus sphaericus tested were highly toxic to Cx. quinquefasciatus but not to the Aedes spp. Clostridium bifermentans serovar. malaysia was more toxic to Ae. polynesiensis than to the other 2 species. Entomopathogenic bacteria merit field testing for larval mosquito control in French Polynesia.