Here is Dr. Prociv’s (and Dr. Carlisle's -they are married) reply to the questions. He is now retired, recently moved (his files are all in boxes where they are not ready to hand), so he is fielding some of these questions from memory without being able to refer to his papers. Ironically, I also have about a two-foot high stack of photocopies & reprints of journal articles on
Angiostrongylus cantonensis boxed and stored in a barn in the Sierra Nevada Mountains where they are completely inaccessible at the moment. Fortunately, however, there does appear to be quite a wealth of newer information available online regarding research on rat lungworm.
Following below Dr. Prociv’s replies are in plain text, questions for him are in italics, with parenthetical remarks and information from me inserted in brackets. He writes:
Thanks for your further communiques. They remind me of something I’d overlooked – the role of paratenic hosts. I recall in Tahiti and the Cook Islands there have been reported outbreaks after people ate raw shrimp [called freshwater "prawn" in Puna] salads, and also in parts of the Pacific, coconut crabs and land crabs have been recognized as sources of Angio for humans. Obviously, the infective L3 can survive passage into certain other host without undergoing further development and from them pass to rats or people. Crustaceans and land planarians have been confirmed, while other species may yet be discovered for this role. These are recognized scavengers that probably eat slugs and snails. I’d imagine that in such cases you’d probably be eating only small numbers of L3s from such paratenic hosts, but that’s all you need for symptoms.
The point about water filtration: from memory, the L3s are about 400 microns long by possibly 20 wide. Sorry, but this could be incorrect; I need my references for specific dimensions, but can’t access them yet -you could try searching online; I’d say a 20 water filter should remove most L3, but a smaller mesh would be even safer.
[Searching online I have located several notes saying
A. cantonensis L3-stage larvae measure 425 to 524 microns in length and from 23 to 34 microns in diameter. If anyone else finds figures different than these, then please do post them. If these figures hold up then they are good news as regards using 20 micron filters on catchment tank water. Research is needed to determine the effect of home in-line UV light sterilization units on L3 as well. My experience during several years in South America was that a combination of physical micropore filter and UV sterilizer worked much better than either method by itself.]
Q:
Here is another question together with some interesting comments in a post to the Punaweb discussion on angio. This is the first time I've heard of using anything prophylactically against angio; any comment on ivermectin as a prophylactic agent for angio in dogs? I've asked for a citation to track down how that 77.5% slug L3 infection number was determined (sounds very specific, perhaps more so than is certain to be the case, so I wonder about the method used).
A: Yep, the problem with killing the worms migrating thru the CNS is that this would simply exacerbate the clinical problem; a dead worm stops moving, starts disintegrating and so stimulates a much more aggressive inflammatory reaction, possibly even serving as a nidus for bacterial infection. If you have worms moving thru your brain, you want them to get out of there ASAP, which is what they’ll do, eventually, left to their own devices. In the young child who died here in 1998 there were hundreds/thousands of maturing worms in the pulmonary arterial system, just as you’d expect in a rat, so these had all obviously passed successfully out of his CNS and were about to complete their life-cycle, i.e. start sexual reproduction. Sadly, this child was simply overwhelmed by a massive infection. Now, the only drug I know that kills nematode larvae in tissues is ivermectin (and its relatives), but it has never been shown to work against migrating L3s in the CNS (and you wouldn’t want that there, anyway, as just explained). However, were you to take the drug just as the L3s were entering your system (from an ingested snail, say), and before they reached the CNS (the window of opportunity is only 1-2 days), then maybe ivermectin would work – as it does for heartworm in dogs (and probably
Toxocara, and even hookworms, and therefore maybe Angio.). So, if people suspect heavy exposure, it wouldn’t hurt to take ivermectin – but when do you stop taking it?!
[Searching online I have located records of animal studies on rat lungworm L3 therapies using albendazole, cucumin, interleukin-12, mebendazole, and a combination of interleukin-12 and mebendazole. The lattermost is intriguing enough to share these summary snippets and source info-
“Treatment with mebendazole in combination with IL-12, however, resulted in low levels of worm recovery and dramatic lessening of the eosinophilic meningitis....This study could be used in developing strategies for the treatment of human angiostrongylosis.”
and
“To address previous doubts that chemotherapy can lead to exacerbation of neurologic damage due to simultaneous death of a large number of
A. cantonensis organisms in the brain, chronological changes in the brains of mice treated with mebendazole at 4 dpi were monitored between 5 to 14 dpi (data not shown). Chemotherapy did not shorten the period before the onset of eosinophilic meningoencephalitis. Eosinophilic meningoencephalitis still first appeared around 11 dpi, as was the case for the nontreated mice. But the severity of meningitis was lessened to a moderate degree due to the lower number of worms.”
Combined Treatment with Interleukin-12 and Mebendazole Lessens the Severity of Experimental Eosinophilic Meningitis Caused by Angiostrongylus cantonensis in ICR Mice
Wen-Yuan Du,1 Jiunn-Wang Liao,2 Chia-Kwung Fan,1 and Kua-Eyre Su1*
Infect Immun. 2003 July; 71(7): 3947–3953.
doi: 10.1128/IAI.71.7.3947-3953.2003.
PMCID: PMC161979
Copyright © 2003, American Society for Microbiology ]
*Edit: Here is the link to the full text of this article; I forgot to insert it with the original posting. The numbers located by the authors' names tie to their contact info at this site.
http://www.pubmedcentral.nih.gov/article...tid=161979
Q:
What I keep not being able to understand is that scientists, including ones with the CDC, say that they find nematodes in the slime of the semi slug, just not that many, and that either no one knows how many nematodes have to be ingested or that you may only need a few to cause symptoms, but that it is doubtful that you can get the illness from the slime. Now, if you have ever gotten freshly slimed by a semi slug, you know it takes much scrubbing and something like clorox to get the slime off. It is incredibly viscous and I can imagine, particularly in this climate, the slime not drying for a little while, allowing the nematodes to stay alive. If you pick lettuce, or green pepper or anything else and just eat it right from the garden, which is what I used to do here years ago, and it happens to have slime on it, this means that you could be eating live nematodes, does it not?
A: Unless more recent work has been done on this, my impression from past studies was that the slime story was inconclusive. In slugs/snails, the L3s settle within muscle tissues, so it’s unclear how/why they’d be leaving for the outside world (although definitely possible). I’m not saying it’s wrong, but that I’d like to see more/better evidence. However, if there really were Angio L3s in slime, then you’d be wasting your time washing the lettuce, as the slime is so tenacious and, when dry, almost imperceptible. I’ve also found tiny snails right in the heart of a lettuce bought from a supermarket!
[This is why I, for myself and my family, will be using a 5 gallon bucket and doing a salt brine soak of veggies which may have infected little slugs hidden in them, then agitating the veggies and rinsing well. The salt brine should cause any little slugs and snails to immediately detach from the leaf surface; soaking veggies for awhile may dissolve any slime with live L3 (if any L3 are indeed present and alive in the slime of those particular veggies after all the rat control measures), and may disrupt the tissues of any L3 which are present. After agitating the veggies again in a second bucket of clean water, a final rinse with distilled water could further disrupt any L3 present in dried slime (which by that point would hopefully have dissolved).]
A, cont.: From my own backyard studies, I discovered that there were lots of different species of nematode larvae (which all look almost identical with each other) in these molluscs; unless you were a specialist in this area, you would confuse the free-living or other parasitic species with L3 of Angio (the differences are subtle, so you’d need to know what to look for, and to examine them very carefully). This might explain the high prevalence of larvae (77.5%) in the local semi-slugs - they might not all have been Angio. Also, finding nematode larvae in slime proves nothing, unless they were confirmed [as via clinical experiments feeding bits of slimed-with-L3-present veggie to certified parasite-free rats and then later, after the appropriate grow-out period for rat lungworm, sacrificing the rats and checking for presence of the worms] to be the culprit – and you’d also want to confirm they [the L3] were alive/infective.
[Indeed, searching online in following up on this comment I found several general surveys of parasites in tropical rats which identified multiple parasites of all different sorts in them. Illustrative and typical is the note that rats examined were “...found to be a host for 9 species of nematodes in Kuala Lumpur and Singapore by Schacher and Cheong (I960). On Tioman
R. sp.
tiomanicus is a host for "at least 7 species of nematodes. Three of these 7 (
Sypiacia maris, Angiostrongylus cantonensis and Ntpposlrongylus brasilieiisis) have been recorded from
R.
r. diardi elsewhere in Malaya. In addition.
R. sp. tiomanicus harbours at least four species of cestodes (tapeworms), one trematode (liver fluke) and a pentastomid (tongueworm). Thus, in numbers of species of parasitic helminths there is certainly no major difference between the commensal
R. rattus of the mainland and the principal commensal (and forest) rat of Tioman.” From: Notes on the Endoparasites, by Frederics; L. Dunn.
So, yes, there are all sorts of nematodes and other helminth larvae present in rats. It is tough to differentiate between some species of helminth larvae so this may affect species-accurate counts in some studies. The main actionable point I take from this, though, is "Kill the rats!"]
Q:
When the semi slug is tiny, and black in color it is does not carry the nematode, according to some studies. Only as it matures and turns grey which is when it is about 1/2 inch and gets up to its adult size of about 3 inches, is it infected with nematodes. Not that you would intentionally eat one of these things, but they could be overlooked and sliced up or put into a blender for a smoothie.
A: I’ve never heard of this study, but it shouldn’t be a difficult one to do. I’d like to see the original paper. It stands to reason that the larger a snail is, the higher worm load it’s going to carry, as these beasts keep on accumulating Angio larvae for life (the L3s stay in its tissues until it dies). However, if you’re going to ingest one of these accidentally, I suppose you won’t have an opportunity to examine it, for size or color! Given that it takes the larva at least 2 weeks to develop in the snail (from the first stage: L1, thru to the infective L3), then perhaps this is sufficient time for the snail to grow significantly in size. I have no idea how fast your slugs/snails grow, but ones I observed here [Queensland, Australia] years ago did it pretty fast, from egg to maturity in a few weeks. The larvae found in a very young one might simply not yet have attained the infective L3 stage.
That’s about all I can say in response to the postings so far, but please don’t hesitate to ask if you have more questions, or need clarification of some points. I reckon there’s a strong case for someone to be doing a little more basic research over there, as this problem sure does have local flavours and variations, and it wouldn’t cost too much to find some answers. (Isn’t your new President a Hawaiian? Maybe he’d be sympathetic . . . )
Dr. Prociv’s comments conclude there.
As Dr. Prociv has noted above, more research is needed. Quite frankly it does not seem to me like the questions which need answering would be too difficult or expensive to resolve at even a modest lab set up for conducting rodent research, as long as someone on the team has a bit of experience in tropical parasitology to oversee the process and confirm valid methods and results. If there are local researchers at the university or in the public health system who would like to lean into this issue with some simple basic experiments, but who lack funding and support, then if they identify themselves I am sure there would be a strong groundswell of enthusiasm from residents of Puna, Friends of Puna’s Future, and others for the Council and other entities to appropriate funds toward such research. This really is an issue for the state of Hawaii to take on (the business of government being business, all too often in practical effect) as it will be a disaster for tourism if more people come to grief and the tourists not only stop ordering salads at restaurants and resort hotels but stop coming altogether. Several Puna locals can sicken and die, apparently, without a big noise arising and heaven and Earth being moved on the issue but if just one tourist child dies then I'd predict all Hades would break loose in the national media. What a black eye for tourism PR that would be.
One last note, in our online discussion the question was asked
“Is there any research what those infected people had in common? Poor hygiene,weakened immune system,etc.?” I am sure the intention was constructive and the comment innocent of any intention to cast aspersion, nor has anyone seemed to take it that way so far, yet in my experience it is important to not unnecessarily associate a stigma of any sort (e.g., poor hygiene, weakened immune system) with an epidemiological issue. Stigma generates shame ...and shame leads to people hiding in embarrassment and fear rather than stepping forward and seeking assistance. When people hide then the accuracy of the picture painted by statistical reporting suffers and it becomes manyfold more difficult to identify and intervene in eliminating pockets of infestation.
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