Ocular onchocerciasis, five years after commencing vector control in the volta river basin

IWORLD HEALTH ORGANIZATION AFRICAN REGION ORGANISATION MONDIALE DE LA SANTE REGION DE L'AFRIQUE ocP/EAC2 ONCHOCERCIASIS CONTROL PROGRAMME IN THE voLTA RryER BASIN ARI,A PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSI DANS LA RLGION DU BASSIN DI] LA VOLTA Til 333 l2- 329 t0-338,57_ Tdli.r ONCHO 5241 UV EXPERT ADVISORY COMMITTEE Second meeting Geneva, 12-I6 0ctober 1981 ORIGINAL: ENGLISH OCULAR ONCHOCERCIASIS, FIVE YEARS AETER COMMENCING VECTOR CONTROL IN TI{E VOLTA RIVER BASIN Though recent studies in Cameroo.rl an,l Nigeria2 have thrown some light on the natural history of ocular onchocerciasis, the evolution of the disease in an area of vector control is not well known. For this reason, andconsidering the need to assess the health anci socioeconomic benefits of control of onchocerciasis, there is an ophthalmological assessment included in the epidemiological evaluation of the Onchocerciasis Control Progranrne in the Volta River Basin area (OCP). The results of some cross-sectional and longitudinal studies on ocular onchocerciasis in an area of successful vector control for five years is reported here. Material and methods 1098 and 94O patients over the age of five years from six villages were given a detailed ophthalmological examination in 1975 and 1980 respectively in a mobile dark-room and the results were recorded for computer analysis. The six villages were all originally hyperendemi-c for onchocerciasis and situated in a savanna area. Results Table I shows the population ophthalmologically examined in 1975 and 198O together with the attendance rate in six clusters. The attendance rate which averaged 77.2% in 197 5 but had fallen to 57.1% in 1980 is likely to become a critical factor in the future fo1low-up studies. Fig. I shows that the prevalence of blindness is decreasing markedly in clusters I, II, IV and VI. In this context not only the incidence of blindness, but also the significantly reduced life expectancy of the blind which_has been demonstrated in the Progranrne area, must be taken into consideration.3 Fig. II shows that the prevalence of ocular onchocerciasis. defj-ned as the presence of visible microfilariae of Onchocerca volvulus in the eye and,/or typical onchocercal ocular lesions has decreased over this period, the overall reduction beLng 28%. In Fig. III it can be seen that microfilarial load in the eye expressed as geometric mean has decreased over the period. Similarly in L-ig. IV the prevalence of severe eye lesions is lower in 198O than in 1975. 2 I iocPfEAC2.2 page 2 Fig, V shows that the prevalence of onchocercal punctate keratitis has decreased considerably in 1980. This condition usually observed in lightly infected patients is believed to be an expression of unimpaired inrnune defence mechanism, whereas in heavily infected patients the i-nrnune defence may be depressed. The distributi-on by age and sex of a cohort population which was examined in both 1975 and 1980 can be seen in Table IL 139 children \.rho were under five in L975 and were therefore not examined ophthalmologically at that time are included. The cohort's composition closely resembles a known standard population from the OCP area. Furthermore, a comparison of a study of the prevalence of ocular lesions in the cohort population and absentees showed a very close similarity. Thus, the composition of this cohort is considered representative from the ophthalmological point of view. Eig. VI shows that the incidence and the rate of loss of visible microfilariae in the anterior chambers of the cohort has an uneven age distribution; the analysis of the results by sex did not reveal any clear correlation. The overall incidence is 6.3% and the rate of loss is 11.8%, givin a net rate of loss of 5.5% over the five years. In comparison with Fig. VII, the incidence rate of microfilariae in the corneae is lower, 2.8% but the rate of loss is much higher, 3L.57". There was a slight, but not significant tendency for the males to have a higher rate of incidence and loss of microfilariae in the cornea, than the females, The interpretation of these results must take into account several factors: 1. Observer variation, which is likely to be more important in assessing microfilariae in the anterior chamber than in the cornea; 2. The possibility of the turnover of microfilariae in the aqueous humour being slower than in the corneal stroma; 3. The consideration of the decreasing intensity of onchocercal infection due to the aging worm population as well as the possibility of infections acquired inrnediately before the beginning of vector control. Fig. VIII shows that the ocular load of microfilariae of the cohort expressed as a geometric mean has decreased over the five-year period of vector control. This decrease seems to occur predominantly in the cornea. Table III shows the incidence of severe ocular lesions and blindness. Wi-th seven new lesions of the anterior segment and fifteen of the posterior segment giving an overall incidence of 1"1. and 2.1% respectively, the incidence of severe ocular lesions seems to be Iow compared with similar studies from the areas of on-going transmission of Onchocerca volvu1us. The anterior segment lesions consisted of one complicated iritis and six cases of early and mild sclerosing keratitis. The inclusion of these six cases of sclerosing keratitis appears to overstate the incidence of severe lesions of the anterior segment of the eye because diagnosis of this lesion in the absence of an associated corneal microfilarial load is becoming increasingly difficult and the assessment of its early stages is subject to observer variation The posterior segment lesions were seven cases with both choroido-retinitis and post neuritic optic atrophy, four cases of isolated choroido-retinitis, one case of choroido-retinitis combined with posterior synechiae of the pupil where the retinal involvement appeared more prominent considering visual function, one case of isolated post-neuritic optic atrophy and a second case of the same lesions combined with early sclerosing keratitis. fn Table IV the distribution by age and sex of patients with severe ocular lesions in 1975 and their tendency to deteriorate by l98O is shown. From 152 anterior segment lesions recorded in 197 5, 10 had deteriorated by 198O; from 74 posterior segment lesions 15 had deteriorated giving the rate of deterioration of I.4% arid 2,I% respectively. Here also the higher rate of deterioration of posterior segment Iesion is apparent. It is significant that more males than females were found to have severe ocular lesions although the same number of eyes of males and females deteriorated over the five years of vector control. I ocP/EAcz.2 Page 3 Table V shows changes in the visual acuities of eyes of the cohort after five years of vector control. The deterioration of visual function was highest in age 30'49 years and least in 5-14 years. More left eyes showed improvement than right eyes but this is not significant. Visual function was considered deteriorated or improved when there vras a change of at least two lines on the visual acuity chart. Eyes which showed altered visual function caused by other diseases e.g. cataract were excluded. Discus sion The prevalence of onchocercal infection includlng the resulting severe ocular lesions and blindness have been shown to be falling five years after vector control in the OCP area which is in accordance with previous studies in Kenya+ showing that nine years after vector control microfilariae were present in only 7.L"/" of eyes of patients examined in a hyperendemic area. The prevalence of severe ocular lesions was correspondingly low and only a few cases of onchocercal blindness were found in people over 40 years. In contrast, studies from Cameroonl i., hyperendemic area of on-going transmission showed 4.5% incidence of severe ocular lesions of the anterior segment and 4.2% of the posterior segment of the eye over a four-year period. After five years of vector control, we found a total of l% of new severe ocular lesions of the anterior segment and 2% of the posterior segment of the eye. The incidence of blindness was 1.6% and all cases going blind so far had severe, irreversible ocular lesions before the beginning of vector control. The prevalence of visible microfilariae in the anterior segment of the eye has decreased and it is not surprising, therefore, that the incidence of anterior segment lesions is low. Sclerosing keratitis particularly, which is normal-Ly associated with a high load of microfilariae in the cornea has been limited to mild stages which actually have no visual functional consequences. Thus the control of the vector is leading both to a reduced incidence of anterior segment lesions, which also seem to appear in milder forms. The incidence of posterior segment lesions, which is believed to occur even in the presence of a relatively low load of microfilariae in the eye was twice as high as that of anterior segment lesions. However it is still less than half of the comparable incidence in areas of on -going transmission. Conc lu s ion Five years of vector control of onchocerciasis has broken the transmission of infection, resulting in a decreasing prevalence of ocular onchocerciasis and a reduced load ofmicrofilariae in the eyes leading to a decreasing incidence of severe ocular lesions and thus breaking the pathway to onchocercal blindness. REEERENCES Anderson, J., Fuglsang, H. & Marshall, T. F. de C. (1976) Studies of onchocerciasis in the United Cameroon Republic. III. A four-year follow-up of six rain forest and 1 six savanna villages Hygiene, 70,362-373 Budden, F. H. (1957) Natural history of onchocerciasis 41, 214 , A,, Vaugelade, J(In press) Roberts, J. M. D., Neumann, C. W. Kenya, nine, 11 and 18 years 37, lg5-2L2 Transactions o the Royal Society of Tropi cal Medicine and 2 British Journal of Onh thalmo I opv La surmortalit6 des aveugles en zone de savane Ouest-Africaine , Geockel & Highton, R. B. (1967) Onchocerciasis in after elimination of the vector. Bul1. Wld. Hlth. Or ostPr3 4 IocP/EACI.2 paSe 4 II III IV V VI Widinaba (Ghana) Mouvielo (Upper Volta) Foungou (Upper Volta) Kayoro (Ghana) Kimpeo (Upper VoIta) Pendie (Upper Volta) Total TABLE I POPULATION OPHTHALMOLOGICALLY EXAMINED IN 1975 AND 1980 IN 6 CLUSTERS IN THE OCP AREA I t97 5 19 80 t97 5 19 80 L97 5 19 80 197 5 19 80 t97 5 19 80 L97 s 19 80 t97 5 19 80 272 475 200 219 309 284 356 380 94 106 423 384 72.32 48.62 83.22 7 8.72 79 .52 85.22 80.42 47 .87" 83.t2 75.82 69.42 40.52 77.22 57 .LZ t 6s4 1 848 Cluster Total census populat ion Ophthalmo 1 ogi cal examinat ion()z 5 yrs) Attendance rate for population(>, 5 yrs) L67 209 754 148 205 207 25L t72 69 69 252 135 1 098 940 ocP fE,AcZ.2 page 5 zttIs oHil H roo N@ O\ O\ * H ]J ]J(0cd o c.l!+J d& H H H H .; H h H a t'IzH z x r:I a & rI]H a F-l(J z F-l o @ o\ H Hz LN F- o\ I zB frl F & th CN azH FJ a tl al]J aI (J H H o H (Z) a7er. ssaupurlg ocP /EAcz .2 page 6 elZIE OHltt H r)0N@O, O, u! cd(u o 0.) !!d(0&&oEllzH I E] cn & E]H a FlO \o f!o o@ o\ i az F- O, zH t/)H a4H C)& rd Qo () zo il *l =Qo rrro td(J z E] F-l tl H H H H H H H H (_, H a tr +J O H o c! o\to\oO@ (Z) aruaIEAa.ld !N ocP/t Acz.2 page 7 ,ttr8 oH,a H roo N@ O\ Ol# i 'rl .i ddoo F.] F] N a ! C)]J o (J H H HH HH a TqH <h F-l C.) zH o @ o\ ri az LA F- Ol i H a o Fl FI H r'. ! FI o&(J H z & ,l DOo z E] H H H .; H h o id H (ueaur J r J:lauroo8 ) aET f, e T T Jo.rc rln J o .ra qurnN 2ocP/EAC} page 8 9 tI t8 olt+l c')$ E o 0) a ! o .: ! 0')]J a oA ]J .: B o. "'1 x --c 'a o. Ha ! L: o'u -: c.rE.: oo .i O! .r-{ ! .rl r!9 !Joo)oitrlir o OO!! la o.io ,oc;o O !froo o.uac, cdqi Oo "io! ou0J o)tr lrc. I o 0J -o tro !oo oEOtlco .i\ rHE AJtrQrd H rnoN@ o\ o\ oJ ql tJ!(d(!&d H H N a&HH <t) F-l(J \o zH o @ OrJ az ro F o\ zl-t * ct)zo H(,/) td ,-1 Fr Td ld& rd t4(n ho E](J z rI] F-l E]d E H H H H CJ H tq H H o c{ocoo -t o i (Z) aDuaTe^a.1d ocP/EAcz.2 page 9 9ttI8 oHA F-.1 rno N@ O\ O\ ..i .i 0J 0) u! d(d&fr o tr OJ ! a iU H H N a& E]H a =FJ(J \o zH o @ o\ i HZ r) F\ o\ = zH aH H .H F-{ dEH rd ts F(J zp o] j (-) & t4Oo (J zo tr1o (-) z rd F-] rI] Ar H H H H F-l o N oo\oO (Z) aruale^ard ocP /EA}Z.2 page 10 TABLE II DISTRIBUTION BY AGE AND SEX OF THE COHORT POPULATION EXAMINED IN BOTH 1975 AND 1980 5-14 t5-29 30-49 >/ 50 Overal 1 M F T M F T M F T M F T 133 106 18 .9 15.1 34.0 L8.2 75 .4 33.6239 92 66 158 98 105 203 13 9 t2.9 13.8 26 .722.5 14.5 54 .3 45 .7 100 .0 1 4 6.3 6.4 8.3 6.3 14 .0 r5.0 ,o o t2 .4 14.6 27 .0 58 44 102 L2.7 M F T 381 32t 702 49.8 50.2 100 .0 * refers to 1980 age ^*Age (years ) No /" OCP standard population (Z) ocPft,^cz.2 page 11 o al atllt? oH/eiOrn ocaO-ifo\ooNo@ a t{(n OJ .l A olr b0 o b0d +o LA \t Io cn o\ c! Itr) il -J'i I rn q 11) d q{ o 0.)! d& q) ]J cd tl OJ U tr OJ .U .i U tr H & rd E t(J &oH & r4H 14EO HCO o\ZaH a H&t^ <NFJ O\Hi ilA(J HQ LP z EaaHXCNrI] H >a E{lrt ZO rrlH s)<OA FJ c{ f4OON rchHO d z rl](J z E]a H() H H ciH tq Ll q) >' .rl A o tr 60 0) b0 c! +o rn o\\t Io ca aJ I L. d i I ooooooooON\orn+ca.i ocPfE\cz.2 pa9e 12 +orn0, T]$ o\ >' rtr o. oO\ tl -r o0 I rao (! o 8llr8 oHLt o i oooooooCON\.otn\tca-l oooooood6 - .o rn 'J c"l a o Fl qr o o! d& rrlz&o() tJ H zo *r (n rdHH(J Oro <co(J o\dl a El(JAoz:E<(JZr^ON Or &14 €-z Ol4z<a E]taz <HH={e4<XF.l ElHl\ cnOH&zc)t4HHEH t4a F-lFqN r-{ o(n F\H >f!o fqo a <no F-1 14o ElF a az rI](J zraH(, zH .$ i I r^ HH CJH fq +o a tl(u Oi A) Iotr A) oO\ tiNOO ILn o)db0 cd a Ir) c.J]J(n tl 0.) o 0.) C) H (Z) ai,ea aruaprcul ocP/ELcz.2 page 13 6t1,19 oHA H rno t-\ @ N H H a&ul t,]HHZa rcDH F-lHC) d.o >H r-lHOH@U: O\ Oipi rQoz:E< Zt^OF- o\zrHHHZH QH .FlH()o H ILl FQ a&cn4Z!H(J<ox rdz<u) E]H TI]fiHOH ZO4o(n c'l HC) o4N n' cr oo a tl o +) o -1 -U H H H H H o i r1 uEarrr Jl.lJauoac ocPh,^cz.2 Page 14 TABLE III INCIDENCE OF IRREVERSIBLE ONCHOCERCAL OC[]I,AR LESIONS AND BLINDNESS a. One case of nultiple lesicars, preilominantly posterior segrrent b. Parenthesis in percentage Age(rears) Anterior bSegnent Posterior bSegnent Incidence of bSlindness. 5-74 M F r lrl F T I*{ F T M F T M F T t5-29 ,o-49 Grerall 1 (o.8) I 1 4 5 (0.+) Il: i] (l.z) 1 (1.0) r (0.5) 2( 5( 0.5L.6 )) 7 (r.o) ,a (z.r) , (t.r) r (r.r)r (r.5) 2 (r.1) 1a 4 (r.(1. li t G.q) I 2 ll.t') , (2.9) e (z.r) 7 (2.2) t5 (z.r) 1 1 1.1 1.5 ) ) z (t.1) 4 1 7 I 1 2 6 , 4.r 2.9, G.+) lt 7))1 (z.o) (r.e) ( r.e) u (r.e) IocP/EAcl.2 paSe 15 TABLE IV DISTRIBII'ION BY AGE AND ffiX OF PATE}II'S WITI{ SEVERE OCUI,AR I,ESIONS n[ 1975 AND TreIR TMIDUICY TO DETERIORATE. Percentages in parenthesis AGE (rmms) A]I'IM,IOR SGMENT POSTERIOR SGMMIT TOTAL LESION RECORDED IN t975 IESIONS DEIERTO- RATEN BY 1980 TOTAI LESTONS RECORNED IN t975 IESIONS DETERIO. RATED 3Y 1980 5-L4 l'1 F T M F T M F T M F T M F T 5 2 1.8 1.8 ) ) 7( L4( 7( 2.9) t5-29 L5.2) 10.5 ) 2L (:-t.z) 10-49 6t (62.2) 21 (20.0) 82(40.4 56.2 47.7 41.2 26.5 15.8 2r.6 ) 77 50 2L2t 42 101 5L L52 ( ) Overall ( ( )) ( ) , (r.L) , (z.a) 6 (r.o) 2 2 4 3.q) Q.s) G.g) 5( ,( L.1)1.6 ) ro (r.4) 7 (r.2) 7 G.9) :-z (rr.o) 4 ( 5.1) 16 (ro.r) 2' L6 (z).+)(ts.z) 19 G9.2) 4 ( 5.8) e (re.z) 12 46 28 74 (r:..e) ( rz. r)( e.z) ( ro.5) r (o.e) 1 (0.4) z (z.z)I U.z) 5 (1.2) 5 (5. 1 (r.rl 5 (r.o) I (5.8) I (z.g) 8 7 r5 tz r) z) (z.r) ocP/EAcz.2 page 16 @ ao \o ot a ts r{l'r\ @ a Frn \oo$ FI ao F{ o a\o N+ N ao\o N$ o a -l F{ @ a F @ FI o $ -rsf I @ a @ r{ a rr\st \o$ o a F{ N N a l'r\ -{ -.1 tn o\o\o tn d a N FI ta\N <r @\o o\ .{ (\I a F{ N \o a Ln o\ st a Fl\o F--o\ \o ao F{ @ a \o $ a\o\o tr\o r{ t ao F{ Nt r{ $ a$ l.r\ o r{ I @ oo N \o atnr\ r{ * a Bo H *e tr1 Er IHE EH rr]o * A Erlo2 #o B * q BO&g H *A E-]Ei EoHd trI Erfrle * afrl(J 4 o 3 trl >r trl H trt tr] Ff trl >r trI Er o H & afr G] >. tr1 Ff 5 Er otr\o\t+ 3 o o\ N I r.n -l srr{ I tr\ H Er FlotrrEOEr aotrroxtrl I FTHooABHHFOHFAo& FtH 5rn HH HE AEf -f. H Hu)dfrl O zo4O () r4 Fl rq H ul .A o 0) + tr o)t{dg .E o sd +t E! o o t{ o)p{ * a ' A-DDMIDUI{ DOC. oCP/-ti\C 2.2 Do m^ 'l uir G-) u r^f To the tltle of table IfI ad.d, : "after five years of .rector controlrf to read as follot"s z INCIDIITCE O,r IilRlIIIrl:iISLil OlilIlOCm.CAL OCiil/tit IffiIOIIS A-i]D BLIi{DI'IISS A.I'T[R I'IVtr YD\RS OF VECTOIT CONTN.OI. Doc. ocP/EAc 2.2 P.eo 'l (i r4-\e L ) Ajouter au titre du tableau IfI : 'rAprbs cinq arrn6es de lutte antivectorielletr pour 1j-re : I],JC]DEI.]C3 DES LESTO|S OC-LiLIISS IITII]-,NTiST3L!S Etr D]I I,A CIDCITE DUfS A LroiioHocttrcostr, ^'\pliEs cIi'lQ A1INEIS DE IUrIrE /INTI-[ECTOitItrtr LE.