Scenario for survival

Letters References I Doerig. CD. eta ,9~5) MoL Biochem. Pa~us~toL ,'O

167-174 2 KJdd. V. etaL (1991) CellGrowth D, le, ;"

85-53 3 Xiang, J. et el. (1994) J, t3iol Charn 269, 15786-15794

4 8ardwell, L. et a~ (1994) Dev B~ol 166, 363-379 " ~ottram. J.C. et al (1994) Pc~rc~sm/ Todc~y i O. 2s3-257 6 Y.I~I. e~ ui. (1~9~) Proc NcJn Acid So U.~ t 93.1130 1~34 7 Gurderson, IH et al (1987) S:~:~e 238. 933 937

Schistosomiasis, t=ibrosi~ and Esophageal Varlces The review by ~,A/iest~ was a welcome addilon to the literature concerning methods and analysis of the disease associated with schistosomal infe~ions, ~vv would hke to comment that, although Iver fibrosis, commo:,Iv associated with schistosomiasis, is a crucial step in the progression toward bleeding varices, no mention was n',ade of the work by 14omeida and co!lea~ues on the correlation beb~,een fibrosis and esophageal vances. In essence, what are the clinical signs '[hat c'ne can use to determine if a patient with fibrosis wil! evolve into a patient wioh life-threatening bleeding vances? In an

attempt to define nsk factors that are assock~ted with hematL~mesls, we pedo,,,~d cross-sectional study companng patlentt who had fibrotic h~ers and hematemesm with those with fibrotic livers alone. The Ask factors wr=re a combination of ( I ) sp!enic longitudinal diameter greater than I I cm, (2) a penportal fibrosis glade ~reater than one. ~nd (J) an esophageal v~rlces p~rade greater than one (Ref. 2). Age, sex, presence of palpable liver and portal vcin diame':er were not assooated with a s,gnificant risk of bleeding after adjustment for potential confounding factors. Fu~hermore, in an attempt to find

Scenario for Survival Long, h.~,d ~h!:~.:.;,,~auoul ,,~echarlisnlsthat operate :o m~inta,,n the host-paras~te balance :n mo!luscan schis*osomlasis has yielded ideas th4t may be r~epresentative of such mechanisms in diverse host-parasite systems. Invertebrates lack immunoolobulins, and ,appear to achieve recognition of foreign agents predominantly by means of carbohydrate-blndiqg proteins (leO.ins) (the 'definite' lect~ns). ~'4odem vertebrates, includingmammals, retaina relianceon iectinsfor the recognitionof microbial invaderS:humo~,] defensive lecdns include mannan-bindin2, lipopolysacchande (LPS)-bindingand C-re.~fve pruteins: ceil-membrane defensive lectinsiqclude several phagocyte receptors (u8.the l~-glucanreceptor),Lymphocyte selectins are at least indirectly defensive, importantly, metazoans also rely on lectins for a venery of housekeeping f~nctlr, ns (eg. platelet a~re~ation) ~.r,d the comect targeting of molecules (eg. aged plasma proteins destined re, clearance by scavenging receptors) and cells (eg, leukocyte trafficking r~gulated by selectin;'l, and for ordedy developmental events (eg. sperm-e~g fusion, establi,,hment m;~4 stabilization of neuronal connections). These I call the 'integrative' lectin~ Whereas lectins that recognize foreign agents will generally elicit aggressive responses like phagocy~osis and nature! killer (NK) cell-mediated cytotox
homeo~,tatic neeC ior inte:?-ation based on matched lechn-glycan spec:qcities imposes a limitation on the ~F.~.,:t,ur.~ .J ca, Dehydrate de~emninants available to i l ~- dHensive lectin repertoire of the or,~anism. I sugge~ that, from the perspective of an infectious agent, this need of the host to ~ei? on a group of lectins and Lheir speofic ',igands for normal housekeeping is the 'Achilles' heel of its internal defense system. It means that the non-self surveillance ;ystem has an unavoidable 'blind spot composed oftnos~ glycans that serve as iigends for the integrative lectJns, it miant apoear that all a partslte needs to do in order to ensure lack of recognition by ~ts host's defense sy~em ~s to mimic one or more of tl,~ ca~Jhydratc stnJctures used by the ho~ in o~cnes* ating its housekeeping functions. Ho~ever, as tl parasite or pathogen exploitation of th~ 'window of opportunity' would pl~ce any prospective host. at a considerable d,sadvantage ~vo things have happened. First, redundancy became a hallmark of primitive immune systems, so that we find t~u~y a vanety of non-self recognition systei ns ~n each individual, Second, the selectr~e press'Jre for an altematiw non-self recognition system ted eventually to the evolut:on of rearrang~noo genes en~od,ng t~ e pnen~- .enal numbs, of ;mmunoglobuim .,nt:body specifiotles, w,fi~ cap.~b,,,~es of recognizing peptide as we',i ,~ carbot )d: tz s~ructures - a development c' ~ely associated .~ ;th clonal proliferation of ,~and-specific lymphoo/tes. Thinking again about invertebn:tes, then, here are the (conjectured) events that lead • (in mollusc-trematode paras,t!sr~ :: le~t) tO host palas~te .=ompatibility. Ind,wdual

8 8eucL M. et aL (1990) Parasitology I00. 191-200

Chr~ r~e~ INSERM U397 Facult~ de M4dccinc 27 Boui~ard JeanMoulin 13385Marseillececlex5. France

a good prophylactic measure, we assessed the prevalence and degree of varices in 32 subjects before and after treatment with praziquantel. We found a significant reduction of grade and prevalence of vances in these subiects (H.M. k;omeida e[ oi.. unpublished), suggesting that, in some cases, th~s drug reverses not of~ly the liver ti! roSis ~,sociated with ~chistosomiasis, but al :o the e.. :~ha.~eal varices.

References 21S-220

2 El-Tom. M. (1994) 6~J. Surg.8', 996-999 James L Bennett Michlgar, S~te Unlvers~ East L~nsing M148824. USA

parasite larvae (m~cio;a) entcr the host (snaii) and. so long as they express the correct (ie. integrat,ve) carbohydrate structures on their surfaces, escape detection. However, metabolic demands of development~nd ~rc'.~.hmake it impossibleto remain peI~nanent!y incognito. Like a spy in his/her host ~vmmur~ity, exploitation of resources in the host society (the host tissues) tmcomes unavoldabie. The ho~'s ph).k-lc~' is. perhaps marginally, shifted eL t of balance. and this provides signals on which redundant recognition systems can cue in. H o ~ immunocytes ,~eakly recognize th: ~. intruder, but the resemb!ance of its ccrbohydrate 'signature' to that of the host elicits a weak rlefensive response. Simultaneously. the parasite ]n~eff'ercs datively with nest immunocyte functions. This intederence is selective, ;a,~etJng those components of the repertoire that .vould be directed a~ainst the trematode: the abilities of imrnunocytes to respond to microbes are not ~argeted. To do so would =~.aed the demise )fthe host. and this would be inconsist~,nt with continued survival of the long-%, .'d trematode, whose complex life cycle r~ quire~ four weeks or more to achieve patency. This model does n,~t exdude a possibie role for a system that is analogous to the 'off'switch' by which host cells avoid cytotoxic a[iacks oy homologous killer cells. In this scenario, parasites mimick li~ands (often carbohydrate~ that serve to maintain an inactive sta&a in a,~.~nima!'s cytotoxic cells (NKs, lympho' >le.activated kliler cells, natural cytotoxic c.'."Ci~oand the like). Ny ~tudent (Lena G~rv 4ok) has suggested that a nest might intenG .~naily 'decorate' a

39

Letters immmmlmmml~L-. desi~'able s>~-nb+o~t with seff #lycan3 it1 order to prote':t id The notion i~ ~h~.t faint recognition of an invader elic,~s we3k defensive responses, against which the parasite oossesses countc~defenses (such as enzymes that _%avenge toxic host products), and that, with conbnued survival of the p.,asite, selective ~n"erference is initiated, +eading to

pat~site maturation and the production and shed of infective larvae, More globally, my message is that (1) it may be productive to consider lectin n?cogn~tion systems as belonging to two maior functional classes ('defensive' and ':ntegrative' in addition to the mechanistically-based C-t),pe. S-type, etc.. classification, which should stand), and that (2) parasitic expioitatior, of defensive

The Importance of Updating Epidemlological Data The importance of food-bon.~ parasitic zoonoses can;lot be overemphasized, as reported recently by Murrell et ai. in Poras+'c.!oL~.~vTodayL.As a result of a session at a meebngat :/..'-,onKaen,Thailand, however, we would llketo bring to light an observation that Murrell et at omitted. We reported a decreasein Ctonorchissinensis infe,.'~Jonamongthe fish of the Sun l'-~oon Lake in centre! Taiwan. At the same time. w~ observed an increase in Haplorchis spp infec-tion in the fish of the lake. which was known to be ~ndemlr for C sinensis about 15 years ago 2. In the ensu~n6 discussion, we were pleasantly suq)dsed by statements from some researchers ~rl Thailand (C. Khamboonruang. Chiangmai University; and S. Tesan& Khon Kaen University) and Korea, (F:.J. Rim. Korea University) that they have also ob~rved 9 qilar phenomenon of the decreasing liver fiuk,~, Op+sthorchis vivemn, and C. sinensis infection in fish. in their respective countries. Our data showed th,~t of the 4223 me+~acerc~.:.~e from a to'~l of 11443 m~tac~rr_ariae :'ollected by artificial gastdc juice digestion of 45 freshwater fish. Hemiculter ,'euciscuius, from the Sun Moon

Bovine

and k3) probably the exclusive use of mammals as its definitive host by C. sinensis, while Haplorchis spp use birds as well as mammals as definitive hosts. "fhese results demonstrated the need to update epidemlolog~cal data every so often,

One and the Same

40

Christopher J. Bayne Department of Z~ulogy Oregon State University 3029 Cordley Hall OP 97~31-2914. USA

so as to reflect the contemporary status of the parasitic infecuon. This brings us to question: can we really believe ~n the ep~demiological figures that appear to be quoted again and again after more ~han a decade? F~nally, we would like to suggest that co-ordinators of future international meetings report similar phenomena that have been observed in different countnes. because it is only at such meetings that such information can be obtained and this may reflect the global trend or perhaps the evolutionary course in which the parasite is heading.

Lake in October 1995, 406't (96.23%) were Haplorchis taichui, 90 (2.13%) H. purr,i!io, two (0.05%) C. sinensis, and the remaining 67 (I.59%) could not be ~dentified because the metacercanae were not fully developed. "Fhe two C. sinensis metaccrcariae were obtained from two of the 45 fish examined. In a bimonthly follow-up parasitologicai survey of 100 Fish. we found that the prevalence of C. sinensis was less than 0.15% of the metacel'cariae References examined. However, the prevalence of I Mun~ll, KD. Cross, J.H, and Haplorchis s~ ) remained greater than 95~. ChongsuphajaisiddhL T. (I 996) Parcls!tol. These ~s~,;Its are in contrast to the Today 12. 171--173 report by Wang et el. ~ more than a decade 2 Chea, E.R. (1991) in Emerg~n~Probtem~;~n ago, ,n which I00 ~sh examined from the Food-borne Paras~t+cZ0onos,s, Impact on Sun Moon Lake were all positive for C Agriculture and Pubhc Health (Cross. J.H. ed.), pp 18'}- 185, SEAMEO Regional Tropical sinensis. Possibie reasons for this decline in Medicine and Public Health Proiect. the prevalence of C. sinensis metacercariae are: ( I ) the disappearance of pig farms Bangkok. Thailand around the lake: (2) increased awareness of .~ 3 VV'an~,j.3. e al. (1980) Naaonal Science the trematode by the lakeside inhal,;tants; ~ CouncilMonthly ROC 8. I i 3 -122

Neosporaand Neesporacanlnum:

During t:,e p-:st decade, the cyst-forming coccidian parasite Neospora coninum has be_on recogn:zed as a cause ot neuromuscuIar disorde~ in dogs. Furthemlore. Neospora.llke organisms have been shown to be a major ca~;e of abortlon in cattle, worldwide. Until 1988. the oa~sit~ ...~.; misdiagnosed as To,,'.~plasma gond~i. Neosporo caninum h~s a wide host ~noe and also p,'oduces mortality in sheep, goats, horses and deer 1. It has be_en sugge.s,ed ,.hat Ne0spu, u ;n dn~s and cattle may not be the same sl" ~.cles? Unti: -ecently there were four known catllne iso!ates o~" N. cu~,num ( N C - I - 3 and NC-Liv) and five ~:vine Ne0spora isolates (BPA I-5). AI! but NC-I iv were isolated in the USA. It has previously been showh that the two species N. caninum and T. ~endii are phylogeneticall K very closely related, based on the high Oe~ree ot -~ouence homology

shortcomings in such a syste, n provided the selective pressure for the origin of imlnunoglobulin antibodies and the vertebrate lymphoid system.

betwee;~ ~heir 16S-like ribosomal RNA (rRNA)-% 16S-like rRNA has been the molecule of choice to study phylogcnetlc rNaticnships because it is the most si," 4,. evolving of the rPNA genes and it has an adequate size. When comparing Neospora iselate~ (bovine as well as canine) originating from the USA. no relevant differences were found wh~!~ ~lionin~ their respccti ~e IG$-iike rRNA sequences s. Recently, we have i':.olated N~:aspora organism~ flora a ~illrJorn calf in bweden 6. The isolate has been designated NCSweBI. Characterization of the i~orate has !nduded ~equence analysis of the ~6S-!ike rRNA and the internal transcribed .%'~cer (ITS ~) ~ well as electron microscopy and ,o~otein analysis. N o differences were recorded with this bovine isolate and IN. cGninom I'~C- I, Previously we have not found any differences in thu

HonE-Kean Ooi Chln~-I Chert Department of Veterirur-i Medicine National Chun8 Hsing University Taichun8 Taiwan

ITSI sequences between the two canine iso'ates NC-I and NC-Liv". In the ITS1 a la~e number of sequence differences exist between N. cantnJm and ~...jondsL Thts does not contradict the previou=~y demonstrated close phylogenetic relationship between N. coninum and T. gondii, as the tTSI is mere vanable than individual rRNA genes. However, within species the ITS1 is consl,~ered to be conserved e Jardine ~ arguea that. mere are nu ukt-astructural morphologLcal criteda differenbating N. caninu:-, In dogs from the Neosporo-like protozo~n of cattle. Furthermore. since no sequence differences have been recorded between Neosporu isolates of bovine and canine origin, for the future we would like to ~uggest mat Oovlne Neu:,pura is rcfen'ed to as N. con+hum until other evidence is presented. References I Dubey, J.P.and Lc,,'+qy. D.S. (t993) PrJrasitol Toddy 9. 452- 458 Pcr~.'~sitolo'~yTodrJy, voi 13, no. I, I'277