Impact assessment of APOC operations: entomology second field trip report Kan (Littoral I, Cameroon), July 1998

a- IMPACT ASSESSMENT OF APOC OPERATIONS ENTOMOLOGY SECOND FIELD TRIP REPORT KAN (LITTORAL I , CAMEROON), JULY 1998 IMPACT ASSESSMENT OF APOC OPERATIONS ENTOMOLOGY SECOND FIELD TRIP REPORT INTRODUCTION There is evidence that large scale distribution of ivermectin reduces transmission by 45- 85%. Furthennore the post treatment pattern of repopulation of the skin by microfilariae indicates that repeated treatment may have an accumulative effect on the reproductive capacity (fecondity) of the adult worms. On the basis of these results, it has been suggested that CDTI could lead to the intemrption of transmission and elimination of infection. How ever, it is unlikely that total intemrption of transmission will occur, and that CDTI will need to be continued for decades to sustain the control of the disease as a public health problem. Given the uncertainty about this issue, the likely geographical variability in the impact of CDTI on transmission and because of the important operational implications if intemrption of transmission were to be achieved, APOC will study the impact of CDTI on transmission. To this end, baseline data should be collected and studies of the reduction in vector infectivity after 5-10 years of CDTI will be undertaken in a selected number of sites representative of the main epidemiological patterns and the principal vector-parasite complexes in ryOC To evaluate the impact of ivermectin based control on transmission, the methodology needs to be defined. It was considered that an appropriate entomological indicator was the level of infectivity of the vector. Tlre changes over a 4-5 year period in any selected area should be available to APOC. During the last APOC workshop in Douala (3 - 16 May 1998), it was agreed that before the meeting in Ouagadougou in august 1998, all groups/teams must have completed their work in site I. To this end, and because the entomologist has to carry out two visits to each site, our second visit to site I was scheduled for the 10'r'to 24't'of July 1998. The visit was delayed for logistical reasons. GENERAL OBJECTIVE To evaluate the long term impact of CDTI on Onchocerca volvulzs transmission. SPECIFIC OBJECTIVE To determine the long term reduction in vector infectivity as measured by tlie number of infective flies (flies with L3s in the head) per 1000 parous flies. METHODOLOGY A 90 day fly collection spread over one year is to be carried out during the coming year. This gives 5 days of field work every month, starting from the month of June 1998 for site I (Littoral I). START OF FIELD TRIP This part of our work started with my journey from Kumba to Yaounde (the capital city) to get contact with the hierarchy. I left Kumba for Yaounde, 425km, by road on 10'r'July as first agreed but the mission could not take place because Dr. Ozoh, the dermatologist could not come from Nigeria. I had, however, got to Yaounde so I took part in the meeting scheduled for the 11'h. This meeting was organised by Dr. Grace Fobi (Team leader) and attended by Dr. Ntep Marcelline (NOTF) the Social Scientist who had just returned from the field and many other persons. I retumed to Kumba on the 14'r' of July after helping in the preparation for the trip. I returned to Yaounde on the 18'r'July, 1898 in company of Dr. Ozoh whom I picked up from Douala airport. TRIP TO SITE I left Yaounde on the 19'r' with a driver as an advance team to arrange for or accommodation and the rest of the team joined us at Ibaykak, our base. The entomology team remained in Kan and started work on the 21" of July 1998. STUDY AREA The villages selected for this study are Kan, Ona, Pendjok, Njoknkong and Ibaykak (4" 05'N 10o 41'E) with a census population of 1500 persons. This zone is rather hilly (highest point 600m) but the Sanaga river is the most prominent geographical feature and is the main source of Simulium flies. The bed of this river is full of huge boulders which render the water flowing over them very turbulent. Besides this, it goes through a series of falls (Eweng : 7m high, Kan : 8m high).The present vegetation is mainly secondary rain forest left behind after logging and fanning with large stretches of virgin forest along the river and on the islands. The climate is equatorial with four seasons with rainfall figures ranging from 2000 to 3500 mm per year. The annual temperatures are generally high ranging from 2l to 29'C (average : 24"C). The average relative humidity is 84oh. SAMPLING OF ADULT SIMULIUM POPULATIONS Two fly collectors working altemately from 7.00 to 18.00 hours daily for five days, collected any Sintulium squamosum that came to take a blood meal on their exposed legs. The standard OCP protocol for data collection and recording was used. The flies collected were dissected to determine the physiological age (parous/nulliparous) and kept in separate tubes in absolute alcohol. The OCP form I (fiche no 1) was used to record the results of the hourly collection. The results of the age determination were recorded in Form 2 (Fiche no 2). SAMPLING OF LARVAL POPULATIONS Several accessible breeding sites were checked and different types of substrates were collected and examined for Sinrulium larvae. STAINING USING MAYER'S HAEMALUM The ethanol was removed by soaking the flies for 24 hours in distilled water. A little amount of preservative was added to avoid fungus/bacterial growth. The flies were then completely covered by the stain after placing them singly in the holes of a microtitre plate. The stain was replaced by water and left to stand for one hour. With time the colour becomes blue- purple instead of deep red. The water was replaced by 25o/o acettc acid. The acid removes excess stain and makes the tissues soft by maceration. This takes between 30 min. to 2hrs. and should be followed by the change of the colour of the liquid. However, one must dissect some flies from time to time to stop the process at the right time by replacing the acetic acid with water, otherwise all the stain will be gone. I{ i DISSECTION Dissection is done on a microscope slide Three flies per slide are dissected in small drops of "dissection medium" (50o glycerol, 25Yo acetic acid, 25o/o water). Care is taken to dissect all mouth parts (the labium in particular) and clear all thoracic muscles from the chitinous body wall, without cutting the muscles into pieces. Each fly is covered by a cover slip (15 x i5mm). To detect filarial larvae, all dissected flies were examined very carefully using a compound microscope at about 60 x magnification. RESULTS Biting Rate 2443 S. squamosunr flies collected during this visit were all dissected. 947 were parous. The daily biting rate (DBR) was 490 flies per man per day. Table I, Fig. 1 show the hourly variation in DBR with two peaks (one in the moming and another in the evening). More flies were collected during the morning period. S. squantosunt larval populations No mature larvae were found in the breeding sites which we visited. The water level is still too variable for larvae to fix on accessible substrates. Parous rate The parous rate (table II) observed during the month of July was 38.8% with the highes number of flies collected during the aftemoon period. Infection Rates The parous flies collected have not yet been dissected due to the difficulties we had with the staining method. This problem has now been solved and the flies are actually being dissected. The results will be ready before the meeting in Ouagadougou. DISCUSSION The Mayer's haemalum we had in our laboratory did not stain the material in a way to allow us to continue with our dissections. We have now got a fresh stain from our supplier and I i 1. the worms stain very well. The staining procedure is rather long and time consuming and will require a very well trained technician to keep up with the rythme of monthly collections. In the protocol it was agreed that 1000 parous flies be kept aside every month for DNA checks in Ouagadougou. It has not been able to keep this quantity of flies for the DNA work. Table I: Hourly variation in daily biting rate for the five days of flies collection in july 1998 A Total number offlres collected gAverage number of flres collected Fieure I : Hourly variation in the biting rate for the five days of flies collection in july 1998 Table II: Dai ly parous rate in july 1998 400 350 300 250 200 (g E ro .c Eo 0) 6() o .9 o q) .o Efz 150 _ 100 I 50- 0- % % % : tr a E a a E o. $ trq ri- E o. N Eo Nj E a E d Eo ! E N Hour 7 -8 am 8-9 am 9-10 am 10-11 am 1r-t2 am t2-l pm | -2 pm z-) pm 3-4 pm 4-5 pm 5-6 pm Total Total number of flies collected 259 165 2t3 247 157 130 1 6 1 134 296 311 375 2448 Average number of flies collected 52 JJ 43 49 31 26 )L 27 s9 62 75 490 Flies caught Flies dissected parous parous rate day 1 393 393 t42 36.13% day 2 6t6 6t6 220 35.7t% day 3 575 570 1,97 34.56% day 4 511 511 2t3 4r.68% day 5 3s3 3s3 t75 4958% Total 2448 2443 947 38.76% Biting rate 490 flies/man/day