Phoneutria - toxicity

Bites from spiders of the genus Phoneutria are common in Brazil. Therefore, and because of the potent venom of some species, studies on the effectivity and composition of their venom have been conducted since the 1920s. During the years it could be clarified that Phoneutria venoms contain a wide variety of peptides and proteins including neurotoxins, which act on the ion channels and chemical receptors of the neuromuscular systems of insects and mammals. This causes excitatory symptoms such as salivation, lachrymation, priapism, convulsions, flaccid and spastic paralysis of the anterior and posterior members and can lead to death following intracerebral injection in mice (Richardson et al. 2006). More than 150 peptides/protein components have been identified and four fractions of neurotoxins could be isolated so far, namely PhTx1, PhTx2, PhTx3 and PhTx4 [PhTx1 acts on Ca2+-channels, PhTx2 affects Na+-channels , PhTx3 acts on Ca2+ or K+- channels and PhTx4 slows down Na+-current inactivation due to glutamate release at neuromuscular junctions but has no effect on mammalian Na+ -channels]. The latter has been proven to be extremely toxic to insects of the orders Diptera (flies) and Blattodea (cockroaches), but also to have much weaker effects on mammals (Richardson et al. 2006). Other results clearly confirmed that venoms of three compared Phoneutria species show qualitative and quantitative differences, despite an overall similarity in components. The most obvious difference is between venom of P. nigriventer (the “synantropic” species) and P. reidy. Venom of the latter species contains a much higher concentration of the components strongly acting on insects rather than on mammals (mice). The whole venom of P. reidyi is about 20 times more toxic for insects than the venom of P. nigriventer. On the other hand is the venom of P. nigriventer more toxic for mammals (mice), than that of P. reidyi (Richardson et al. 2006).

It may be worth mentioning here that another interesting study on P. nigriventer has shown that males are less toxic than females, and females guarding an egg sac are a bit more toxic than females without egg sacs (Ramos et al. 1998, Herzig et al 2002, Martins & Bertani 2007).

Since it is an important aspect of Phoneutria, we offer here some more details from studies concerning Phoneutria bite envenomation. Clinical-epidemiological studies give differentiated information about the severity of Phoneutria bites.

However, we emphasize that even if some of these studies show that these spiders are rarely extremely dangerous for humans, this should nobody entrap to see it as a challenge or an invitation to “handle” Phoneutria species incautiously!

Throughout several years Bucaretchi and coworkers studied effects of arthropod venoms on humans, including that of Phoneutria: from a clinical-epidemiological study summarising 422 cases of patients (9 months to 99 years old) bitten by Phoneutria ssp. (data collected from January 1984 to December 1996) they report that 75.2 % were bitten in limbs (feet 40.9%, hands 34.3%). Most patients presented only local complaints, mainly pain and edema. Patients were classified due to their symptoms as presenting mild (89.8%), moderate (8.5%) or severe (0.5%) envenomation. Few patients (1.2 %) did not present signs of envenomation at all. The severe envenomations were only confirmed in two children (9 months and 3 years old). Both developed acute pulmonary edema, and the older died 9 hours after the accident. Patients older than 70 years, had a significantly higher frequency of moderate envenomations compared to the 10-70 year old patients. Groups with the highest risk are therefore children under 10 years and patients older than 70 years. Only 2.3% of the patients (two cases classified as severe and eight as moderate, eight of them in children) were treated with i.v. antiarachnid antivenom. In conclusion, accidents involving the genus Phoneutria are common but cases of systemic envenomation in adults are very unusual (Bucaretchi et al. 2000). Until 2008, ten deaths were attributed to Phoneutria spiders in Brazil, but in only two of these cases were sufficient details provided to allow comparison with other series of patients (Bucaretchi et al. 2008).