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ARTIGO DE OPINIÃO/OPINION ARTICLE
Venomous mollusks: the risks of human accidents by
Conus
snails
( Gastropoda: Conidae) in Brazil
Moluscos peçonhentos: riscos de acidentes em humanos pelo molusco Conus
( Gastrópode: Cunidae) in Brazil
Vidal Haddad Junior
1, 2, João Batista de Paula Neto
3and Válter José Cobo
4ABSTRACT
Mo llusk s o f the ge nus Co nus pr e se nt a ve no mo us appar atus c o mpo se d o f r adulae , a c hitin str uc tur e link e d to glands, whic h inj e c ts po te nt ne ur o to xic pe ptide s, c ausing se r io us human e nve no matio n and e ve n de ath, asso c iate d with the b lo c k age o f c e r tain r e c e pto r s and musc ular par alysis. No r e po r te d e nve no matio n has o c c ur r e d in B r azil, b ut c e r tain po pulatio ns ar e at r isk o f ac c ide nts.
Ke y- wo r ds: Co nus. Ve no mo us animals. Ve no mo us mo llusk s. Human e nve no ming. B r azil.
RESUMO
Os mo lusc o s do gê ne r o Co nus apr e se ntam um apar ato ve ne no so c o mpo sto de uma r ádula quitino sa ligada a glândulas de pe ç o nha, c ausando e nve ne name nto s humano s gr ave s e me smo ó b ito s pe la aç ão ne ur o tó xic a induto r a do b lo que io de vár io s r e c e pto r e s e par alisia musc ular. Não há c aso s de sc r ito s de e nve ne name nto no país, mas de te r minadas po pulaç õ e s c o r r e m r isc o de ac ide nte s.
Pa la vr a s- cha ve s: Co nus. Animais pe ç o nhe nto s. Mo lusc o s ve ne no so s. Enve ne name nto s humano s. B r asil.
1 . Fac uldade de Me dic ina de B o tuc atu da Unive r sidade Estadual Paulista, B o tuc atu, SP. 2 . Ho spital Vital B r azil do Instituto B utantan, São Paulo , SP, B r azil. 3 . Pr o gr ama de Assistê nc ia à AIDS, Mo ç amb iq ue . 4 . De par tame nto de B io lo gia da Unive r sidade de Taub até , Taub até , SP.
Addr e ss to : Dr. Vidal Haddad J unio r. Caixa Po stal 5 5 7 , 1 8 6 1 8 - 0 0 0 , B o tuc atu, SP, B r azil. Te le fax: 5 5 1 4 3 8 8 2 -4 9 2 2
e - mail: haddadj r @ fmb . une sp. b r Re c e b ido par a pub lic aç ão e m 2 0 /4 /2 0 0 6 Ac e ito e m 1 0 /8 /2 0 0 6
M o l l u s k s i n c l u d e s o m e o f th e m o s t we l l - k n o wn inve r te b r ate s. Phyllum spe c ie s pr e se nt a spe c ialize d c hitin to o th- lik e fe e ding str uc tur e ( the r adulae ) that c an gr ind thr o ugh the she lls o f o the r animals1 9. The c lass Gastr o po da
inc lude s mar ine , te r r e str ial and fr e shwate r snails, limpe ts, nudib r anc hs, slugs and ab alo ne s.
CONUS SNAILS
The mo st spe c ialize d gastr o po ds may b e the c o ne snails, genusConus, in whic h the radulae is reduc ed to a few iso lated veno m-inj ec ting teeth, the so -c alled to xo glo ssate radulae, that ar e link e d to ve no mo us glands. The har po o n-lik e te e th ar e disc har ge d fr o m the e nd o f a lo ng pr o b o sc is that c an b e
e j e c te d r apidly to c aptur e its pr e y ( Figur e s 1 and 2 ) . The Co nus ge nus pr e se nts a unique spir ale d she ll.
The great majority of cone snails feed on other mollusks and bristle worms. However, some species are piscivorous, presenting the most potent toxins and they can cause fatal envenomation in humans7 1 3
. The most important piscivorous Conus are present in the Indo-Pacific area, such as C. geographus ( the species most asso c iated with human deaths), C. aulic us, C. mar mo r eus, C. striatus C. textile and C. tulipa. There are about two dozen Conus species in Brazil and the most important are C. centurio, C. clench, C. c lerii, C. ermineus,, C. jaspidus, and C. regius1 0. Moreover,
species like C. clerii, C. jaspideus and C. regius feed actively on marine worms and present active toxins2
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Ha dda d Júnio r V e t a l
Figur e 1 - Co nus snail in attack po sitio n, sho wing the pr o bo scis and the r adulae, str uctur es capable to enveno ming with gr avity human beings.
VENOM ACTION OF THE CONUS SNAILS
T h e ve n o m o f th e Co n u s s p e c i e s i s c o m p o s e d o f c o no to xins, whic h ar e ne ur o to xins o f lo w mo le c ular we ight. The ir ac tio n is e xtr e me ly fast, whic h is c o mpatib le with the slo wne ss o f the snail in its e nvir o nme nt and the c o nse que nt diffic ulty invo lve d in c aptur ing the po iso ne d pr e y.
Th e a c tio n o f th e c o n o to xin s o c c ur s b y b lo c k a ge o f musc ular and neur al r ec epto r s7. Ther e ar e two differ ent to xin
Figur e 2 - A live spe cime n o f Co nus o f Mo z a mbique – India n Oce a n – sho wing the pr o bo scis ( pr o ba ble Co nus impe r ia lis) .
effects in the venom. The first, the “lightning-strike” effect, causes immediate immobilization of the injected prey through peptides that inhibit voltage-gated sodium channel inactivation, as well as peptides that block potassium channels. Together, this combination results in a massive depolarization of any axons in the immediate vicinity of the venom injection site, causing an effect similar to electrocuting the prey. The second effect is achieved more slowly and involves total inhibition of neuromusc ular transmission through conopeptides, which act at sites remote from the venom injection site, such as neuromuscular junctions. The motor cabal effect, found in all fish-hunting Conus venoms examined so far, includes peptides that inhibit the presynaptic calcium channels that control neurotransmitter release, the postsynaptic nicotinic receptors, and the sodium channels that underlie the muscle action potential2 0.
Cur r e ntly, c o no to xins ar e a valuab le to o l o f sc ie ntific r e s e a r c h , d u e to th e i n te n s e p h a r m a c o l o gi c a l a c ti vi ty pr e se nte d b y the pe ptide s. One o f the dr ugs in c linic al te sts is zic o no tide , whic h is a pe ptide that b lo c k s the ne ur o nal c alc ium c anals with exc ellent effec t in the treatment of c hronic and se ve r e painful pr o c e sse s1 6.
CLINICAL ASPECTS OF THE ENVENOMATION
T h e e x a c t n u m b e r o f p r o ve n d e a th s c a u s e d b y e nve no matio n b y Co nus she lls is no t k no wn, tho ugh ab o ut 5 0 s uppo s e d o c c ur r e n c e s a r e c ite d. En ve n o m a tio n c a n simulate o the r c ause s o f de ath, lik e myo c ar dial infar c tio n o r c er ebr al isc hemia, and may no t always be c o r r ec tly identified. The inde x o f mo r tality o b se r ve d in e nve no matio n b y Co nus she lls r e ac he s 2 5 %7.
A typic al ac c ident invo lving Co nus shells, initially pr esents inte nse b ur ning pain at the site o f the sting, whic h e vo lve s in ab o ut o ne ho ur to pr o gr e ssive par alysis o f the b o dy musc le s witho ut o ther lo c al sympto ms o r signs. Histo r y o f c o ntac t with th e m o llus k a s s o c ia te d with in te n s e m us c ula r we a k n e s s sho uld r aise suspic io n o f an ac c ide nt. In late r phase s, the patient c an develo p palpebr al pto sis, blur r y visio n and speec h and de glutitio n diffic ultie s, unc o nsc io usne ss and dyspno e a, with po ssib le e vo lutio n to r e spir ato r y ar r e st that c an b e fatal and o c c ur s 4 0 minute s to 5 ho ur s afte r the sting3 7 9 1 2 1 3 1 5 1 7 1 8.
In B r azil, thr e e spe c ie s o f Co nus o f lar ge diame te r ar e po tentially danger o us: C. r egius, C. c entur io and C. er mineus, the last o f whic h is pisc ivo r o us3 1 1.
C. e r mine us was ide ntifie d in the Fe r nando de No r o nha Islands6, whe n studie s r e gar ding
its high toxic ity and the potential risk for human envenomation alr eady existed1 8 4. Currently, ho wever, there is no safe c linic al
info r matio n r e gar ding the spe c ie s o f Co nus fo und in B r azil o r th e o c c ur r e n c e o f p o s s ib le a c c ide n ts , a lth o ugh th e p o s s i b i l i ty o f e n ve n o m a ti o n , e s p e c i a l l y fo r B i o l o g y pr o fe ssio nals and she ll c o lle c to r s e xists.
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availab le antive no m e xists at pr e se nt1 5. Se ve r ity de pe nds o n
the time passed sinc e enveno matio n and o f the full installatio n o f the manife statio ns, with so me c o nside r atio n give n to the sting site . A lac k o f me dic al r e so ur c e s also influe nc e s the pr o gno sis. Enve no matio n b y the Co nus ge nus is r ar e , b ut it is po ssib le in r isk po pulatio ns and the gastr o inte stinal and ne ur o musc ular sympto ms in patie nts sho uld no t b e c o nfuse d with alime ntar y po iso ning.
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