Greetings TWiP team. Here are my thoughts on the TWiP 150 Case Study.
From the description of the rash as ‘1 cm long brown lines, clotted blood deltas at end’ my first thought was Cutaneous Larva Migrans caused by migration of animal hookworm larvae into the human epidermis.
However the locations of the rash and the short length of the brown lines make me think that a more likely diagnosis is scabies, caused by small mites Sarcoptes scabiei burrowing in the skin.
Further reading reinforces this idea, the itch of scabies is described as insidious and relentless and often worsening over a period of weeks and is typically worse at night. The scabies burrows are described as brownish irregular lines with scaling at one end and sometimes a vesicle at the other end.
The scabies mites are less than half a millimetre long but should be visible in skin scrapings with a low power microscope.
Scabies will not resolve without treatment. It can only be cured with prescription medications that kill the mites, there is also a danger that scratching could lead to secondary bacterial skin infections.
Permethrin is approved for use in people 2 months of age and older and is considered to be the safest and most effective treatment for scabies. Ivermectin is also effective but is contraindicated in young children.
While medications can kill the mites and eggs quickly the itching and rash may initially become worse, there can be a persistent allergic reaction to the dead mites. Antihistamine pills can help control the itching and topical hydrocortisone cream may also be of benefit as can antibiotics to treat secondary bacterial infections.
A cháirde (ah khawr-djeh) TWIP,
Greetings from Dublin where the sun has finally appeared, temperatures at a relatively scorching 16 C.
To investigate this case study I was joined by parasitology lab mates Gwen Deslyper and Paula Tierney.
The rash made us think of hookworm, schistosomes and scabies. Schisto was quickly dismissed due to the line marks observed. After lots of consulting images of cutaneous larval migrans and scabies rashes while micro dissecting Daniel and Dickson’s description of the images, we settled on scabies. This was largely due to the lines being described as linear and also 1cm long which does seem too short for hookworm. I know Daniel said that he would like it if people were able to realise that they can start making diagnosis based on what they have already learnt, without consulting the literature, but we are currently 5 for 5 on TWIP, so are not taking any chances. Literature confirmed that scabies is endemic in Panama, common in children, found on all the body parts where it was observed on the boy and itching increases at night. So we would like to lock in our answer as scabies caused by the skin mite Sarcoptes scabiei. Confirmation by examining skin scrapings under microscope for adult mites or eggs. Permethrin treatment of the whole family.
I have been slowly listening to the back catalogue of TWIP on my commute. Every now and then I come across something I would like to comment on but put it off until I am fully caught up. However something was said in episode #105 that I didn’t want to forget. Vincent mentioned having a copy of J.D. Smyth’s “Introduction to Animal Parasitology”, signed by W.C Campbell. How cool! Dickson said Smyth was a British parasitologist. I will have to indulge in the popular Irish pastime of correcting famous Irish people being called British. James Desmond Smyth was born in Dublin, Ireland 1917. I walk past his portrait every morning on my way to the lab. One of my favourite stories of his time at Trinity College Dublin is how he enthused a young student in the field of parasitology by inviting him to join him dissecting a fish, which he removed tapeworms from. The young student was W.C. Campbell. Whenever I see students getting excited when finding their first parasites in wildlife hosts, I now think another potential future Nobel laureate.
Another point that keeps coming up when listening to the back catalogue is the debate over the ability of Toxoplasma gondii to influence non rodent host behaviour. It may come up in an episode I have not gotten to yet, but just in case I thought you might be interested in this paper “Morbid attraction to leopard urine in Toxoplasma– infected chimpanzees” Poirotte et al. 2016 Current Biology.
Alice writes: – winner!
Good morning, hosts!
Alice here writing from Syracuse where it is a beautiful spring morning: bright sunshine, blue skies and 3C right now, warming to 10C later today. The best part: no snow for next few days! As you may know, Syracuse is the frequent winner of the Golden Snowball Award, a snowfall accumulation contest between five central New York cities. We are set to take the crown again with 153.6 inches (390.1 centimeters) of snow so far this season.
But enough about the snow…on to the case of the six-year old boy with Cutaneous Larva Migrans. I base my diagnosis on the intense itching, rash location/morphology, and presence of definitive hosts (dogs). It was mentioned that many children in this village have this rash, which they likely picked up playing in soil contaminated with Ancylostoma braziliense larvae. Dickson mentioned that the rash had a “serpiginousity” while Daniel remarked it was more linear which is a little puzzling, but given the length of the lines and lack of other symptoms, it sounds like creeping eruption. Oral anti-helminthics such as ivermectin or albendazole would take care of the worms, and not playing in contaminated soil would prevent re-infection.
I look forward to the next podcast! Thank you for all that you do.
Alice Wood Fox
Senior Research Support Specialist
Hi TWiP hosts,
I’m going to jump straight into the case study this week! My guess is scabies, caused by the human itch mite Sarcoptes scabiei. The fertile female parasites burrow into the hosts skin to lay her eggs, and the molts/faeces of the young in the tunnels are what cause the itchiness and rash, though this is usually delayed by a week or more. Scabies is known to be worse at night, which is experienced by the boy. I suspect the “1cm brown lines” are the tunnels dug by the females. Diagnosis is commonly completed by viewing a skin scraping under a microscope, and would treat with an antiscabetic such as Permethrin. However the symptoms may last a little while after treatment as the dead mites would still cause irritation.
Thanks for the great case study! I really enjoy using them to keep my parasite knowledge up to date.
I am writing in with my case guess for the itchy children from Panama described in TWiP 150. I vowed to guess again no matter what the case as I heard you read the responses to the case in TWiP 149. I didn’t write in with a guess even though I would have got it right – my diagnosis was cutaneous Leishmania but I thought it was too soon after the last case of Leishmania so I searched for an alternative explanation and found none. My stupidity lost me another shot at winning a book! Oh well… My guess for the new case will have to be cutaneous larva migrans. It’s caused by larvae of animal hookworms ending up in human hosts and not being able to complete their life cycles due to missing/different environmental clues. Where animals are free to wander and defecate in soil hospitable to the L3 larvae humans can pick them up when they penetrate the skin. Daniel mentioned that the rash he saw is common in children in this area. My thinking is that young children crawling/sitting on dirt floors in combination with a wide variety of animals being around could easily lead to CLM. According to PD6, an inflammatory reaction to the migrating larvae develops within days of penetration and PD6 also lists the common areas of the body where such rashes occur – including the arms, trunk and genital area as reported in our case. Treatment of choice is oral antihelminthic therapy such as albendazole or ivermectin.
If I am right and I happen to win the book I’ll add it to ScienceGrrl Glasgow’s ever-growing library and take it out with me on our outreach missions. Fingers crossed!
Sara in Glasgow
Centre for Virus Research
greatly enjoyed your recent podcast, which I just discovered. I studied parasitology and medical entomology in 1980 and the Liverpool School of Tropical Medicine but haven’t really worked directly in the world of parasitology. TWiP 150 cries out for an immediate diagnosis, but in order to avoid the ‘availability heuristic’, where one relies on the first thing that the memory recalls, I suggest making a little list of possibilities. (ref for the availability heuristic: Thinking Fast and Slow, Daniel Kahneman, 2011). I used to exhort medical students and residents to make a 3 item differential diagnosis (at the very least) before fixing a definite diagnosis. Your last podcast involving the ulcer of cutaneous leishmaniasis could have benefited from a little digression into other ulcer etiologies such as cutaneous tuberculosis, yaws, sarcoidosis etc. before fixating on the ‘one true thing’.
Differential diagnosis for TWip 150:
poultry lice bites, e.g. Menacanthus stramineus
fungal infection, e.g. ringworm though not very consistent with clinical case
However, the likeliest candidate diagnosis is infestation with Sarcoptes scabiei. The dermoscopy findings are typical (see reference) as are the facts of the rash distribution and itch that is worse at night. Children are often more affected due to their tendency to increased skin to skin contact. I saw a case at the Salvation Army clinic in Chicago in the 1990s in an alcoholic who lived in a shelter. He appeared to have typical ‘Norwegian scabies’. I was able to obtain skin scrapings and identify the mite under low power microscopy. I applied lindane from the neck down, thinking him incapable of fastidious application of the remedy to every nook and cranny. A few weeks later I saw him, vastly improved.
Please consider mentioning delusions of parasitosis, which can afflict more sensitive patients who are diagnosed with worms and ectoparasites. The diagnosis can get under their skin.
Thanks for a great educational and entertainment service!
Kevin Carney MSc(Liverpool), MD
Crusted Scabies Marta Elosua-González, M.D., and Elena García-Zamora, M.D.August 3, 2017
N Engl J Med 2017; 377:476
recent study in Fiji using ivermectin
December 10, 2015
N Engl J Med 2015; 373:2305-2313
Mass Drug Administration for Scabies Control in a Population with Endemic Disease
Good dermoscopy picture.
BMJ Case Reports 2009; doi:10.1136/bcr.06.2008.0279
Diagnosis of scabies by dermoscopy
It’s been a while since I was in central America, but I don’t need to travel far to find a kid with scabies. The intense itching, excoriation and distribution of the rash put this high up in the differential for this case.
The symptoms are caused by an immune response to female Sarcoptes scabiei mites tunnelling through the epidermis, depositing eggs and feces as they go. Transmission is by person-to-person contact. Dermoscopy is an accurate and practical way to confirm diagnosis. Dr Griffin described a characteristic appearance of a linear (or serpiginous) burrow trailing behind the triangular head of the the mite.
Treatment is with topical permethrin for the whole family, repeated after 2 weeks. Oral ivermectin also works well. Secondary bacterial infection is common. Scabies is a disease of poverty, apparently endemic in that part of Panama. Community health education and access to primary care can reduce its impact. Mass drug administration may be an option.
It was great to hear more about the Floating Doctors – volunteering with them is on my to-do list. If it ever happens I’ll send you a case study.
iHasta la próxima vez!
I’ve really enjoyed your show since a colleague in my lab introduced me to it a few weeks ago, and I was tempted to send in my diagnosis last week, but didn’t trust my own judgement even though I had thought cutaneous leishmaniasis so I thought I’d give it a go this time round.
I admit that most of it has been through googling the symptoms and some quick searches of pubmed but let’s see if it’s right. I won’t go into too much detail, but I’ve arrived at the conclusion of ectopic cutaneous schistosomiasis. Having skimmed a few papers on the subject after googling the symptoms it seems to fit, the presence of the water toilet, and the close proximity to rivers, streams etc in the area lead me to this conclusion, along with the characteristic rash, which according to the paper cited below is a common sign of this type of schistosomiasis. It makes mention of groin, genital area rash, with spread to the trunk as well. Photos I have seen in the process of looking up these symptoms seem to match your descriptions as well, so I am hazarding a guess, I look forward to hearing your next show.
I thought I’d add a bit about my work as well here, as it could be interesting, especially with regards to diagnosis in these remote settings, and I decided I’d include this when you mentioned about the lack of pcr etc in these resource limited settings.
I’m currently working on a project at the University of Bristol, in the virology dept, on LAMP, which if you’re not familiar is an isothermal pcr like assay which uses 6 primers which form dumbbell structures with self annealing loci, allowing for exponential target amplification, and a strand displacing polymerase which removes the need for expensive thermocyclers. We have been optimising this for dengue virus diagnosis, but it can also be applied to parasites and bacteria as well. We use a colourimetric detection method based on pH change, so no downstream analysis is needed, and it can be used as a single tube assay with a high degree of sensitivity. Using a device plugged into a laptop or portable power pack, or even a smartphone all that is required is to heat the reaction mix to 63c for 1hr to achieve detection of down to several ng of target dna, or rna due to rt inclusion in the mix. I thought this might be an interesting topic for discussion as this area of diagnostics for resource limited settings is an area I am very interested in and I believe that this assay has great potential to expand the diagnostic capabilities of mobile clinics/Drs like you described in your show.