Monthly Archives: September 2011

Deadly Organism of the Fortnight: Lonomia obliqua.

This fortnight’s selection is a vicious caterpillar from the rainforests of Brazil & its neighbours.

Lonomia obliqua.

As you can already see, this critter has vivid aposematic colouration (Bright colours can indicate danger to predators, especially in caterpillars) and lots of urticating hairs. Now most caterpillars with urticating hairs can be a major hazard insofar major dermal irritation and itching is concerned, but Lonomia obliqua is exceedingly lethal due to its venom.

Envenomation often occurs when people accidentally brush against a group of these caterpillars on tree bark or on the floor et cetera, the results aren’t pretty; Lonomia obliqua envenomation is due to a venom with haemolytic properties; post-onset, recently healed wounds may re-open and start to bleed, there is massive internal bleeding that manifests in haematuria (blood in the urine) and out of other orifices, there can also be brain haemorrhages to compound the misery of anyone who experiences envenomation from these caterpillars.

The venom contains fibrinolytic proteases that breaks down fibrin (which is essential in the coagulation of blood) and also causes bleeding elsewhere by sequestering clotting factors. Light was shed on what the venom contained and the relevant cDNA sequences after someone did a little study. I hope you will find the paper illuminating insofar understanding the mechanics of Lonomia envenomation is concerned. You can find the paper here.

The paper also has in significant detail a census of the protein families involved and putative targets in the human clotting cascade that stand to be affected. Happy reading.

That paper is slightly outdated, but still provides valuable insights with respect to cataloging the overall composition of Lonomia venom. A newer paper, which I’ll link to later in the post, explains the points of action of components of the venom wrt the human clotting cascade.

Rather paradoxically, Lonomia obliqua venom works by activating the blood clotting system, which consumes the resources needed by the body to prevent bleeding elsewhere, and consequently leads to the massive bleeding described above. A protein called Losac activates Factor X and a protein called Lopap activates Prothrombin.

The blood clotting cascade is as follows, and may help you locate the points of action of the aforementioned proteins.

Blood clotting cascade; should help you locate points of action of L.obliqua venom.

The paper I mentioned is a case study, and may be found here.

That is all from me with respect to this fortnight’s deadly organism. I’ll leave you with some particularly nasty Ecchymoses (large bruises under the skin) from the case study.

Ecchymoses from Lonomia envenomation , Image credit; Canadian Medical Association