Seroprevalence of Toxocara canis infection in tropical Venezuela

Tru~s~crro~sOFTHEROYALSocr~n OFTROPICAL MEDICINE AND HYGIENE (1988)82, 275-281

Seroprevalence

of Toxocara

canis infection

in tropical

275

Venezuela

Neil R. Lynch’**, Kim Eddy’, A. NeiU Hodgen 3, Reina I. Lope2 and Keven J. Turner’ ‘Clinical Immunology Research Unit, Princess Margaret Hospital for Children, Box 0184, Perth, 6001, WesternAustralia, Australia; *Institute de Biomedicina, Aptdo 4043, Caracas, Venezuela; 3Serology Section, State Health Laboratory Sties, Queen Elizabeth II Medical Centre, Perth 6008, Western Australia, Australia

Abstract An enzyme-linked immunosorbent assay (ELISA) was used to determine the seroprevalenceof Toxocuru canis infection in different &o-economic groups of the trot&al oooulation of Venezuela. The lack of de&&e ind&ndent diagnostic criteria for toxocariasis required the establishment of operational upper limits of normality for Toxocura ELISA values, based upon their log-no&al&d distribution in a presumptive “non-tox ocariasis” sub-nomdation. Onlv 1.8% of urban subjects of medium-high socioeconomic level were considered to be clearly positive in Toxocuru ELISA, compared to 20.0% of urban slum dwellers, 256% rural subsistence farmers and 34.9% Amaxon Indians. As the test was performed using excretorysecretory antigen, and under conditions of competitive inhibition by soluble extracts of non-homologous parasites, co-infection by common intestinal helminths, protozoa or other organisms did not give rise to false positive results. However, strong crossreactivitv with Onchocerca volvulus may have influenced the prevalence figure obtained for the Amaxon Indians. These results indicate that T. cunis is yet another parasite that is widely distributed in economically underprivileged tropical populations. Introduction Toxocariasis is the infection of man by the dog nematode Toxocara canis (SOULSBY,1983). The life cycle of the parasite is not completed in the human host because larvae, upon hatching from ingested fertile eggs, penetrate the intestinal mucosa, enter the portal circulation and eventually become encysted in various organs. The larvae are, therefore, prevented from returning to the intestinal lumen to mature into adults, and neither eggs nor larvae are passedin the faeces. As a consequence only non-specific clinical criteria are available for the presumptive diagnosis of the infection. The latter include eosinophilia, hepatomegaly, fever, coughing or wheezing, lassitude, and anorexia, amongst other diffuse symptoms (GLICKMAN & SCHANTZ,1981). Even in the relatively rare casesof ocular invasion, the subseauent visual impairment that may occur can be wr&gly attributed to retinoblastoma (SHIELDS, 1984; SEARLEet al.. 1981). Serodiagnosis of the infection therefore assumes Particular immn-tance. and the use of an enxvmehrilred immtuiosorbent assay (ELISA) has proved to be of areat value (GLICKMAN et al.. 1978: DE SAVIGN?et al., 1979). Applying this test, the prevalences of infection in different selected, but presumably normal, temperate populations have been reported to be generally less than 5% (GLICKMAN &

SCHANTZ, 1981; DE SAVIGNYet al., 1979; MATSUMURA & ENDO, 1983; HERRMANN et al., 1985), although depending upon the geographical area or social condition of the subjects, this can be higher (HERRMANNet al., 1985; VAN KNAPIZNet al., 1983; NICHOLASet al., 1986). Special risk groups have also been identified, these including children with histories of pica or geophagia, and dog-breeders (GLICKMAN & SCHANTZ, 1981; WORLEY et al., 1984; WWDRUFF et il., 1978). Virtually nothing is known of the prevalence of Toxocuruinfection in the tropics, where infection with a wide range of intestinal parasites is common. The antigenic cross-reactivity that may exist between other parasites and T. cunis (WELCHet al., 1983; SPEISER & WEISS, 1979; POLDERMANet al., 1980) raises the possibility that reported prevalence figures for toxocariasis are undulv< hiah -. (GLICKMAN & SCHANTZ. 1981). We have applied the Toxocuru ELISA to sera from different socioeconomic moups in Venezuela, with degreesof intestinal parasi’tosisranging from very low to extremely intense. The test employed was based upon the use of second-stagelarval excretory-secretory antigen (TcESA) and the presence of soluble non-homologous parasite extracts to inhibit competitively any cross-reactivity. Our results indicate that T. canis is yet another parasite with a high prevalence of infection in the tropical environment, and perhaps should be considered when assessingthe problem of endemic helminthiasis. Materials aad Methods S&Y Popularions Details of the Venezuelan populations studied are given in Table 1. These essentially healthy individuals were evaluated as part of a wider investigation of various Venezuelan so&-economic levels (SEL), and the selection criteria, clinical testing, etc. have been described elsewhere (LYNCH et al., 1983,1984,1987). In addition to these subiects, patients with various other infectious diseaseswere-evaluated. These were made available throuah different Sections of the Institute de Biomedic&., and were almost entirely of low SEL. Included in thrs group were parasitologically or clinically confirmed casesof leishmaniasis (36 patients), Chagas disease (24 patients), strongyloidiasis (29 patients), onchocerciasis (23 patients), and leprosy (119 patients). Apart from these patients, 21 subiects of medium-hiah SEL who were found to be infected by one or more species of common intestinal parasite at the time of the serological study were also considered.

276 Parasite antigens The excretory-secretory antigen of T. canis (TcESA) was prepared by in vitro maintenance of second staxe larvae (DE SAVIGNY, 1975). Briefly, fertile eggs-were obtained from the uteri’ of gravid female T. canis removed from the intestine of doxs killed at the local pound. The eggs were left io embryonate, then hatched mechanically to allow migration of the larvae in a Baermarmapparatus. The larvae were maintained at a concentration of 103/mlat 37°C in Minimal Essential Medium (Commonwealth Serum Laboratories, Melbourne, Australia) until their viability fell significantly. During this period the culture medium was regularly collected, concentrated by ultitration (PMlO, Amicon, Lexmgton, Mass., USA), and its protein content estimated by the Folin-Lowrv method. The preparation of extracts of a wide range of other parasitesis described elsewhere (LYNCH et al., 1988). These included Ascaris lumbricoides,Necator americanus, Ancykxtoma duodenale,Trichurts trichiura, Enterobius vermicularis, Strong&&s ram’, Schistosomamunsoni, Taeniu spp., Dirojilariu immitis, Entamoeba histolvtica. Giurdia lamb&. Leishmunia SDD. and Tryp&os&na crwi. A mixture of these *parasite extracts, each at a final protein concentration of S@nl, was used to inhibit competitively crossreactivity in the Toxocara ELISA, by its inclusion at the step of serum incubation. Toxocara ELISA method In principle, the test described by DE SAVIGNY et al. (l-979) ias employed. Polyvinylchloride microplates (Flow Laboratories, Irvine, Scotland) were sensitized with lug/ml TcESA in pH 9.6 carbonate buffer. then washed and dried. Serial dilutions of the ’ test serain phosphate buffered saline containing 0.1% Tween 20 (Sigma Chemical Co, St Louis, Missouri, USA) were incubated, in the presence of the nonhomologous parasite extracts, in the microwells for 2 h at room temperature. After washing, these were incubated for a further 2 h with 1:2000 dilutions of goat anti-human IgG, IgA or IgM, conjugated with a&lm;$xphatase (Tago Inc., Burlmgame, CaliforI The reaction was developed using p-nitrophenyl phosphate in diethanolamine buffer (Sigma 104 phosphatase substrate tablets) for approximately 30 min, then stooned bv the addition of 2M NaOH. The optical d&y ai 40Smn (OD& was measured using an automatic microplate reader (Multiskan, Flow Laboratories). The time of incubation with substrate was determined by allowing a 1:400 dilution of standard serum, included on every plate, to reach an OD*s as close as possible to O-65.To allow direct comparison between plates, all test values were corrected by multiplication with a factor that was the ratio of the actual standard value to O-65. The reference serum used was a laboratory standard that had been titrated against sera from the Toxocaral Reference Laboratory, London School of Hygiene and Tropical Medicine, and the Parasitic Diseases Division, Centres for Disease Control, Atlanta, Georgia, USA. Also included in each plate were control positive and negative sera, the former being used to calculate the coefficient of variation between tests.

Statistical analysis The results were analvzed usina the SPSS/PC programe (SPSS Inc., Ch&go, Ill&ois, USA) runninn on an IBM PC/XT. Logarithmic transformations, general statistics, frequeicy distributions, normal curves and correlations were all performed with ,the assistance of this package. Results

of the Toxocara ELISA A range of sera, from weakly to strongly positive in the Toxocara ELISA. were titrated (Fix. 1). and a fixed final dilution of 11400was se&ted for subsequent tests. A selection of positive sera was also compared using anti-&G, anti-IgA or anti-IgM conjugates, and as the ELISA values with anti-IgA or anti-IgM were all less than 10%of those obtained with anti-IgG (results not shown), only the latter was used in subsequent screening. The overall coefficient of variation between intratest duplicates in this study was 6*8+7*8%, and that between inter-test controls was 119%. Characteristics

Churacteristics of the different Venezuelun population groups studied The different socio-economic or racial/cultural groups evaluated in this study are described in Table 1. A gradation in the degree of helminthic infection from -he medium-high SEL in the urban situation throuah to the Amaxon Indians is indicated bv the progr&sively increasing percentagesof intestinal parasitoses, eosinophilia, and total IgE levels.

2;~

lZZ:fA

values in diffhvnt

Vewzuelan

- -Figs 2 &d 3-represents the distribution of ELISA values (ODmq at a serum dilution of l/400) in selected groups‘of thy Venezuelan population. It ‘can be seen that the distribution of these values is highly skewed, but that this is normal&d by logarithmic transformation.

0.5

Fig. 1. Titration of selected ssm in Toxocam ELISA. Curves 6 attd 12, Amazon Indians; 26 and 60, urban slum dwellers. Std.=Rcfawtce standard serum.

277 Table &Characteristics Population group Urban, mediumhigb SEL’

of the different Venezuelan population groups studied.

No. examined 281

% Male 38.2

““CYS SD 18*7+12*7

Intestinal parasitosis (W 12.9

Eosinophilia w 45f 3.8

urbsn slum dwellers

60

51.1

13.6f12.0

57.7

ll*l?

6.8

Rural subsistence farmers

86

49.4

18*4+12*7

65.9

13*7f 7.7

21*9+12-O 83.3 25*3+12*8 49 30.8 Amazon Indians ‘Geometric mean of total serum IgE level (values in parentheses are means plus one standard deviation). *SEL = So&economic level.

%

a.

1W

% 14

b.

a.

654 (2393) (E) lH)88 (34743)

b.

32

10 so

x

u1

Total IgE’ (Iu/ml) 281 (1156)

32

I 60

40

20

0

log 00 4osnm

LO .5

.9 1.3 1.7 2.1 OD 405nm

OD 4OSnm

x

log 00 4% “In

Fig. 3. Log-unnsfotmeddistributionof ELBA values.a, “Normal” group (skewness = - 0.2); b, “toxocnriasis” group (skewness= - 05). Selectedmid-points of the log ODM) ntn intervals are shown,and the normal curvessuperimposed.

SEL, and this was particularly evident from the Amazon Indians whose levels were also signikantly higher (P
groups than in the medium-high

24

1

of Toxocara ELJSA cut-off values To define values that could be considered as threshold levels for the classification of Toxocuru ELISA results as either positive or negative, various descriptive statistics were calculated for 2 groups. The first was a presumptively “normal” population of 235 individuals, defined as being urban subjects of medium to high SEL who did not concurrently have Toxocara ELISA values greater than 8 times the group median (O-162)and eosinophilia greater than 12%. A presumptive “toxocariasis” group of 33 subjects was taken as those of the same SEL, who simultaneously had Toxocaru ELISA values and eosinophilia exceeding these limits. Table 3 shows the mean plus 2 and 3 standard deviations, the 97.5 percentile and 95% confidence interval of the normal group. Also shown are the mean minus 2 and 3 standard deviations, the 5th

Detemination

1 00

4OSnm

OD 4OSnm

Fig. 2. Distribution of ELBA values in different groups. a, Medium-bigb SEL (skewness= 7.1); b, urban slum dwellers (skewness= 1.5);c, rund subsistence fvmers (skewness= 1.2); d, Amaxon Indhns (skewness= 1.1). Normal curves are superimpaged.

Table 2 shows the ranges, geometric means and dispersions of. the ELISA values in sera from the different populations. The levels were significantly greater (P
278

percentile and the 95% confidence interval of the presumptive toxocariasis group. Because considerable overlap occurred between these 2 groups, for the purposes of the present analysis the mean plus 2 and 3 standard deviations of the log-transformed ODW5values of the normal group (Fig. 3, a) were taken as low and high cut-off points respectively (ODM5 of 0.178 and 0656). Positivity of Toxocara ELISA study gmups

Venewlan

by sex and age in the

population

Table 5 presents the percentage of positivity in the 2 sexesand different age groups considered. The only notable difference observed was a lower positivity at the high cut-off level in children younger than 5 years. No significant correlation was found between age and Toxocara ELISA values in any of the study groups. F”tiity

of Toxocara ELISA

of Toxocara

Population group

ELISA

in different Venezuelan

Percentage positive’ Low cut-off High cm-off

Urban mediumhigh SEL

11.4

1.8

Urban slum dwellers

65.0

20.0

Rural subsistence farmers

64.0

25.6

Amazon

81.4

34.9

in different Venezuelan

Table 4 shows the percentagesof each study group that were above the low and high cut-off values. The positivity of the high prevalence parasitosis groups was vastly greater (P
Positivity of Toxocara ELISA

Table 4-Poaitivity study groups.

in different infectious

The percentage positivity of Toxocara ELISA in sera from patients suffering different infectious diseases is shown in Table 6. When patients with clinically diagnosed leprosy, Chagas disease, leishmaniasis, strongyloidiasis or onchocerciasis were con-

Indians

‘% of group with log-transformed ODMs values greater than mean plus 2 (low cut-off) or 3 (high cut-off) standard deviations of normal group.

Table I-Poaitivity of Toxocara Venezuelan population.

ELBA

by sex and age in

Percentage positive* Low cut-off High cot-off Males (171)’

36.6

10.9

Females

32.7

11.8

<5 years (41)

30.2

4.7

6-15 years

391

14.8

31.1

10.1

(240)

(168) >16 years

VW Table Z-Toxocara ELISA values in different Venezuelan populatioa groups (OD,).

‘No. examined in parentheses. *See foomote 1 on Table 4.

Population group

Range Min. Max.

Urban mediumhigh SEL

omo

Table 6-Poaitivity diseases. -.

urban sltml dwellers

Geometric’ mean

G.M. + 1 SD’

2.294

0.021

0.111

omo

1.753

0.239

0.897

Rural subsistence farmers

0.002

1.636

0.223

0916

Amazon IndiatB

0.026

2.214

0.426

1.164

‘Anti

log of mean (plus 1 SD) of log-transformed

Table 3-Descriptive statistics for Toxocara medium-high socio-economic level.

“fqo~“4

“Toxocariasis”

ELBA in different infectious

positive percentage’ Low cut-off’ High cut-off 32.7 31.6 19.4 73.9 10.3 14.3

Leprosy (119) Chagas disease (24) Leishmaniasis (36) Onchocerciasis (23) Strongyloidiasis (29) Miscellaneous intestinal parasitoses (21)

ODN5 values

ELBA

of Toxocara

‘See foomote

values in presumptively

7.6 6.5 11.1 43.5 6.9 0

1 on Table 4.

normal or toxocsriasis

Venezuelan sera from

Median

Geometric mean

Mean’ +/- 2SD

Mean +/- 3SD

97.515 Percentile’

95% Confidence3 interval

0.013 0.269

o-013 o-344

0.178 0.099

0.656 0.053

0.104

0.176

0~011-0~016 0.276-0.436

‘OD 405corresponding to mean plus standard deviations calculated from log transformed values of normal sera, and mean minus SD for toxocariasis. '97.5 percentile for normal and 5th for toxocariasis. 3Calculated on log-transformed OD 405 nm values. %kewness and kurtosis of normal group: 1.57 and 1.94 respectively for untransformed values, and -0.23 and -0.86 after log-transformation.

279 sidered. it was found that, for most of these except onchocdrciasis, the positivity was significantly lower (P
tv surrounds the interpretation of the results and the definition of levels of positivity (NICHOLAS et al., 1986: SCHANTZet al.. 1979). Whereas a number of authors have titrated’ the test sera in ELISA, the dilution that can be considered diagnostic, and that confers optimal sensitivity and specificity, has varied between different studies (SHIELDS et al., 1979; CYPRESS et al., 1977; SEARL et al., 1981; GLICKMANet al., 1979). In epidemiological screening, the use of a llxed dilution of the test serum is more practicable than titration, and in a detailed analvsis of the problem it was concluded that no cne means of expressing the results is free from drawbacks (DE SAVIGNY & VOLLER, 1980). The fact that these difficulties exist when the test is applied to sera from Caucasian populations in temperate climates suggests that particular care should be taken when set-afrom tropical groups are screened. A major factor complicating the analysis of tropical sera is potential cross-reactivity with the wide range of other parasites to which the subjects might be exposed (WELCH et al., 1983; SPEISER& WEISS, 1979; POLDERMAN et al.,

1980). The use of TcESA rather than larval or embryonated egg extracts confers a relatively high degree of specificity on the assay (GLICKMAN et al., 1985; POLDERMAN et al., 1980; CARLIER et al., 1982; DE SAUGNY et a!., 1979), and this can be greatly improved by premcubation of the test sera with Ascuris extract (GLICKMAN et al., 1985; CYPRESSet al., 1977). By combining the use of TcESA with competitive inhibition by a mixture of non-homologous parasite extracts in ELI+, we have shown that the specificity of the assay m tropical sera can approach 90% (LYNCH et al., 1988). The problem remains, however, of the determination of positive/ negative cut-off values under these assay conditions. In the absence of reliable independent diagnostic criteria for toxocariasis, the establishment of a normal range of Toxocuru ELISA values is difficult (GLICKMAN et al.. 1985; CypRESSet al.. 1977). Even if a group of cl&ically proven toxocariasis patients can be evaluated, overlap between the lower limits of disease-

related titres and the upper limits of normality will probably occur (SCHANTZ et al., 1979). In the present study we have attempted to define a “normal” population by considering the ELISA values (ODM5 at an optimal serum dilution of 11400) of individuals of medium-high SEL in the tropical urban environment of Caracas, Venezuela. As eosinophilia is a common characteristic of toxocariasis (GLICKMAN & SCHANTZ, 1981), and in temperate populations the combination of the presence of this with sign&ant ELISA values gives a predictive value (ELLIOTT et al., 1983) of 0.81 (compared to 0.55 for ELISA alone), individuals both with eosinophilias above 12% and Toxocuru ELISA values above 0.162 were excluded from the Venezuelan “normal” group. These latter individuals were, in fact, tentatively considered to form a “toxocariasis” group. Eosinophihas above 12% were selected as being suggestive of toxocariasis because this value was greater than the mean plus 2 standard deviations of the whole medium-high SEL, and because, in this SEL, infection with common intestinal hehninths alone infreauentlv resulted in eosinonhilias greater than this (unpublished observations): The choice of 0.162 as the cut-off noint for the Toxocuru ELISA values in this initial analysis was somewhat arbitrary, although it was based t&m the suggested use of g times the ~XOUD median value (SPEISER& GOTTSTEIN, 1984). In-order to determine statistically meaningful upper limits of normality, the markedly skewed distribution of the Toxocuru ELISA values of the above-defined Toxocuru-negative group were logarithmically transformed, and the mean plus 2 and 3 standard deviations calculated. These values can, on theoretical grounds (DE SAVIGNY & VOLLER, 1980; SPEISER& GOTTSTEIN,1984), be considered to represent cut-off points for “possibly positive” and “definitely positive” ELISA results respectively. In terms of actual ODas values, these low and high cut-off points represented O-178and O-656. It is relevant to remark here that the 5th percentile of the presumptive “toxocariasis” group, 0.176, was closely comparable to the first of these. When the reactivity of sera from the different Venezuelan study groups was considered, it was found that the geometric mean ELISA values of the urban slum dwellers, the rural subsistence farmers and the Amazon Indians were from 10 to 20 fold greater than in the medium-high SEL. The highest ievels were found in the Amaxon Indians. From the noint of view of wsitivitv in ELISA, a comnarable scale of differences between these groups was seen. Taking the high cut-off value, 1.8% of the mediumhigh SEL could be considered definitely positive in the Toxocuru ELISA. This falls into the general range of positivities reported for Caucasian populations in temperate climates (GLICKMAN & SCHANTZ, 1981; DE SAVIGNYet al., 1979; MATSUMURA& ENDO, 1983; HERRMANet al., 1985), desnite the fact that 13%-of these subjects were harbouring one or more different intestinal narasites at the time of studv. The positivities of the urban slum dwellers and the rural subsistence farmers were comoarable at about 20%. and over 30% of the Amazon I&ians had substantial: Iv raised ELISA values. The latter observation will possibly require further evaluation, as, in parts of the Amazon basin, filariasis is endemic (RASSI et al.,

280 1977), and we found what appears to be an excessively high positivity in the Toxocura ELISA for patients infected with Odwcerca volvulus. who had a nositivity of 43.5% compared to 25.6% in th; rural subsistence farming group to which they belong. The only filarial antigen present in the inhibition cocktail used in the Toxocara ELISA was Diroflaria immitis, and until sufficient Onchocerca antigen is available it will be d&cult to evaluate the extent of remaining cross-reactivity, which could be substantial (SPEISER & G~TTSTEIN, 1984; SPEISER & WEISS, 1979). In the only comprehensive study of seropositivity in a tropical population yet reported, a prevalence of 86% was found (THOMPSON et al., 1986). In this study the sera were preabsorbed with Ascuris extract, and titres of > 1:32 were considered nositive. This figure is comparable with the 81.4% found for the Amazon Indians when “nossiblv nositive” ToxocaraELISA values were cons‘idered: We believe that the definitive determination of Toxocuru seropositivity in heavily parasitized tropical nonulations will be difficult until the intluence of 811 potentially crossreactive infections can be fully taken into account. It is interesting to note that, in the present study, positivities in the Toxocura ELISA for patients with leprosy, leishmaniasis, Chagas disease or strongyloidiasis were in fact lower than in otherwise normal subjects with the same background (6.9 to ll*l%, compared to 25.6%). The reason for this is not clear, because in general the normal subjects formed the control groups for the diseased patients, thus reducing sampling error. As these are chronic diseases in which no generalized immunosuppression is evident, it could be postulated that some component of the immune response against the infecting organism cross-reacts sufficiently with T. canis to confer a degree of resistance to this nematode, and that these common antigens are not present in the TcESA preparation used in the ELISA. Another possible, although superhcially less likely, explanation is that, due to the detection of their diseased state, the level of personal hygiene of the patients is improved, and they thus experience lower exposure to T. canis eggs. The positivity in the Toxocaru ELISA of individuals of medium-high SEL, who were found to be infected with one or more of a variety of intestinal parasites at the time of study, was not signi&antly different from the whole group to which they belonged. This indicates that, under the test conditions employed, cross-reactivity with these parasites does not interfere with the interpretation of the Toxocuru ELISA results. In the present study, no evident relationship was found between sex or age and positivity in the Toxocaru ELISA. Although in some populations males and young children have exhibited the highest prevalences (DE SAVIGNY et al., 1979; WORLEY et al., 1984; REE et al., 1984; GLICKMAN & SCHANTZ, 1981), this is not the case in all study groups (NICHOLAS et al., 1986; MATSUMUFU & ENDO, 1983; GLICKMAN & SCHANTZ, 1981). We can conclude from our studies that toxocariasis is yet another hehninthic infection with widesnread distribution in the tropical environment, that his up to the present received little attention. Further studies will be required to ascertain the contribution of this parasitosis to the overall morbidity of such populations.

Acknowledgements

Support was received from CMRF/Telethon project 95, CDCHiUCV project M.09.24185and Conicit X1457. Miss C. Jones provided excellent secretarial assistance.

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Polderman, A. M., de Vries, H. & Van de Water, T. P. (1980). Serological diagnosis of toxocariasis: the use of larval antigens in the ELISA. Actcr Leid&, 48, 37-42.

281 Pollard, Z. F., Jarrett, W. H., Ha er, W. S., Allain, D. S. & Schantz, P. M. (1979). ELI f A for diagnosis of ocular toxoc2arik. ophrhal?nology, 86, 743-749. Rassi, R., Monzon, H., Castillo, M., Hemandez, I., Ram&z-Perez, J. & Convit, J. (1977). Discovery of a new onchocerciasis focus in Venezuela. BuUerin of the Pan American Health Orgattizarion, 11, 41-44. RCe, G. H., Voller, A. & Rowland, H. A. (1984). Toxocarkis in the British Isles, 1982-83.B&i& Medicul Journal,288, 628-629. Schan~~ P. M., Meyer, D. .& Gliclcman, L. T.. (1979). Clh3111al;~=l. Fd epidermologtc chaqctertsucs .of mmcmr3oumal ofTmptcal hiedutne a?td Hygiene, 28, 24-28. Searl, S. S., Moazed, K., Albert, D. M. & Marcus, L. C. (1981). Ocular tox oariasis presenting as leuhocoria in a patientwith low ELISA titer to Toxocara canis. Ophthalmology, 88, 1302-1306. Shields, J. A. (1984). Ocular toxomriasis: a review. Survey of o#dhaho~, 28, 361-381. Shields, J. A., Felberg, N. T. & Federman, J. L. (1979). Discussionof presentationby Dr Zane F. Pollard et al. OfMalmo~, 86, 750-752. Soulsby, E. J. L. (1983). Toxocarkis. British Veminay Jotonal, 139, 471-475. Speiser, F. & Gottstein, B. (1984). A collaborative study on larval excretory/secretory antigens of Toxocara cunis for the immunodiagnosis of human toxocariasis with ELISA. Actu Tmpica, 41, 361-372,

1Short

Report 1

WHO Expert Committee on Onchocerti,

3rd report.

Geneva: World Health Organization. 1987. Technical Report Series No. 752, 167 DD. Price: SW. fr. 24.00. This is the report of the committee that met in April 1986. Its DUXDOS~ was to “reassess the global public health and- socioeconomic importanie of onchocerciasis, and review the advances...that have taken place during the past 10 years, relating them to feasible and practical improvements in treatment and control and to future research needs”. All these the report does, covering everything from DNA probes for Onchocerca volvulus to the economic benefits of

Speiser, F. 81Weiss, N. (1979). Comparative evaluation of 7 helminth antigens in the enzyme-linked immunosorbent assay(ELISA). Eq~erientia, 35, 1512-1513. Thompson, D. E., Buudy, D. A., Cooper, E. S. & Schantz, P. M. (1986). Enidemioloxical characteristics of Toxocara crmis &on&c -infection-of children in a Caribbean community. Bulletin of the World Health Oqpnisation, 64, 283-290. Van Knapen, F., Van Leusden J., Polderman A. M. & Franchimont, J. H. (1983). Visceral larva migrans: examination by means of enzyme-linhed immunos&ent assayof human sera for antibodies to excretory-secretory antigens of the second-stage larvae of Toxocum cunit. Zeirsclrrifi j3ir PamnunRMdc, 69, 113-118. Welch, J. S., Symons, M. H. & Dobson, C. (1983). Immunod.iagnosis of parasitic zoonoses: purification of Toxocara canis antigens by afhnity chromatography. Zntemational3oumal for Pa&to&, 13, 171-178. Woo&u& A. W., De Savigny, D. H. & Jacobs, D. E. (1978). Study of toxocaral infection in dog breeders. British Medical 3ouma1, ii, 1747-1748. Worley, G., Green, J. A., Frothingham, T. E., Stumer, R. A., Walls, K. W:, Paltalnis, V. A. & Ellis, G. S. (1984). Toxocam canis mfection: clinical and epidemiological associationswith seropositivity in kindergarten children. 3oumalof ZnfectiousLkeases, 149, 591-597. ~;;kwd

9 March 1987; acceptedfor publication 14Jttly

onchocerciasis control. The West African Onchocerciasis Control Proaramme is considered in some detail, and the fasci&ing clinico-pathological aspects of the disease are well summarized. The recommendations for future studies are unsurprising. Since the meeting occurred some time ago, the status of Ivermectin is only briefly dealt with. The short list of 20 references is odd and arbitrary: three relate to other filariae. One feels that either a more comprehensive list, or none at all, would be better. Apart from this, the report provides an excellent overview of the entire subject of human onchocerciasis, useful both as a quick crash course an.z$ background reading for more specialized Sebastian

Lucas