Cullen writes:

Good afternoon,

I just finished listening to TWiP 153. I almost didn’t submit a guess for the last case study because I thought I was going to be late, but I am very glad I did now. I was also pleased to hear someone else follow up on the term “peeps.” Yes, peeps is short for people. I’m glad you guys got a kick out of that. I was not at ASM Microbe, but my boss was there looking for a new sequencer and MALDI-TOF. I always enjoy listening to your podcast. Thank you for everything you do on TWiM, TWiP, TWiV, and Immune. I wish I could have seen you in action at ASM Microbe, but I guess that means I’ll have to catch a live recording later.



Lucian writes:

Dear Twipanosomes,

This is a minor comment, but I think an important one. I think it was when Daniel was speaking about soldiers in the Middle East getting Leishmaniasis where he used the past tense: “when we had soldiers in the Middle East” (I am paraphrasing).

I just want to remind folks that the US still has regular troops in Iraq, Syria, and Afghanistan. Last year, there were 26,000 troops deployed to the three countries, though the Pentagon announced a drawdown in Iraq starting in February of this year; I am not sure the total now. The wars in the Middle East and central Asia never truly ended.

Case guesses:

Alex writes:

Hello all,

Given how my guess went last time I figured I would try again to see if I can do it again.

So I have to say that I like how Parasitic Diseases is laid out, made it really easy to go to the back of the book towards the section I needed.

My guess would be that the Man in the City, has crab lice (Phthirus pubis), or the papillion d’amour. Crab lice can produce a “Blue spot”. They are often transmitted through sexual contact.

Crab lice can be treated by applying a pediculicide to the affected areas, yet another word for me to look up, a quick Wikipedia search led me on to seeing that ivermectin was approved for treatment of pediculosis and that gasoline was also used to treat head lice (Pediculus humanis capitis). Resistance to drugs was also noted. Per Parasitic Diseases, permethrin 1% is the recommended treatment for head lice, which the book also said that head and crab lice can be treated similarly. Clothing should be washed and dried by exposure to heat, about 70 degrees Celsius for 30 minutes. Also I would suggest that recent partners also get checked out and treated to prevent spread.

Is there any chance for louse-borne diseases?

On another note, every time I have looked for the TWiP webpage I have always gotten the “This Week in Photography” page, I have learned my lesson and just bookmarked your page.

Chris writes:

Hello Professors,

It is a sunny and beautiful day at 82 F with  a slight breeze here on long island. I believe that the patient from episode 153 is suffering from  a case of genital lice. based on the symptoms presented and the fact that he is sexually active with multiple partners means that he could have easily picked  up this parasitic louse that is known to cause itching of the genitals. Additionally, because you could see it with just a magnifying glass leads me to believe that it is pubic lice.  Another possibility for what it could be is also scabies, as this parasite can also cause intense itching of the genital region although these tend to present with visible lines and also infect the hands. If I win the book please let someone else get it as I already have a copy that I have displayed proudly in my office.

On an unrelated note, I recently went sampling in Alaska for parasites and I have attached a picture of the parasite Schistocephalus solidus because I thought you might all enjoy seeing how large this parasite is in comparison to its host. This tapeworm species has a three host life cycle between a copepod, the three spine stickleback, and some sort of waterfowl. Schistocephalus solidus can make up to 90% of its host body mass! Truly fascinating.

Warm regards,


Courtney writes:

Dear Vincent, Dickson, and Daniel

Greetings from Omaha, Nebraska where it is approximately 79 degrees Fahrenheit and cloudy.  Our weather the past few days has been relatively mild.

I am a masters of biology at the University of Nebraska-Omaha studying bee populations at Glacier Creek Preserve, a prairie owned and managed by the university.

My guess for this week is  Phthirus pubis, or the crab louse.  I’ll admit, I’m a bit too lazy right now to do a differential.  

Here is an interesting article I found on reddit regarding malaria test without using blood.  Mr. Gitta had been tested four times for malaria with the first three reflecting negative results. He then designed and made a device that clips on the finger and scans the blood for changes.

The best,

Peter writes:

Bonjour professors TWIP,

You commented on how my current working in Montpellier France may prevent the TCD parasitology group from sending in answers. Although we did not reach the time synced approach of Bill Gates that Daniel suggested, (rhymes with twipper it’s) Gwen Deslyper and I did email back on forward on what it might be.

Vincent is right though that it is a lot of fun trying to solve the case as a group. It has also been a good excuse for us all to get together as we are in different offices throughout the building. I will be travelling for a few weeks, but when I get back to France I will see if I could get people here listening with me before I return to Ireland. I’m not sure if an Irish guy, they don’t know very well yet, saying he has something interesting for them to listen to and then playing two guys talking about pubic lice would be the best first impression though!

So yes I believe the gentleman has pubic lice or the crab louse (Phthirus pubis) due to the characteristic blue spots. Blue spots resulted in the ruling out of stongyloides, but I am curious if Daniel knows of any other pathogens that may cause blue spots? Lice can be confirmed by trying to comb them out and viewing under microscope. According to PD 6th edition treatment with dusts, creams lotions and shampoos. Also heat treating any sheets, combs, clothes etc. that may have been contaminated.

Also I know at TWIP you are very interested in science communication. I thought I should mention labmate Maureen Williams, who did a great job winning many rounds of the famelab science communication competition, championing parasitology all the way. Here is her national final talk on protecting parasites (

A bientot,

Peter Stuart


Eric writes:

Hello TWiP hosts,

This patient’s history of recent new sexual contact, intense itchiness, and seeing “things” (like moving, living lice?) all suggest that he has acquired pubic lice, Phthirus pubis. But as a habit I should also consider what else it could be.

A very common cause of itch in the groin would be tinea cruris. Tinea is the growth of any of several fungus species on the surface of moist skin, including athlete’s foot and ringworm. When tinea occurs in the folds of skin at the groin, it is called tinea cruris. However, I posit that the presence of the itch even in abdominal hair hints that the rash follows the hair, not the moisture. Also, blue spots are not associated with tinea, I read, but describe pubic lice bites. Lastly, I’m sure there are non-infectious itchy rashes in the groin as well, though I do not know any off the top of my head.

Should our patient be screened for other sexually-transmitted infections?

And a question that popped into my head: Do we know how common pubic lice is nowadays compared to 50 or 100’s of years ago? Do the lice taxa that evolved with our species now qualify as endangered insect species, or are lice far from eradication even in developed countries?

Thanks again for the intriguing cases.


Los Angeles

Daniel writes:

Yo peeps!

My guess is that your patient with itchy private parts has pubic lice.

The organism – Pthirus pubis – is a blood-feeding obligate ectoparasite of humans. The lice are transmitted by close physical contact and occasionally via fomites. They live on coarse body hair. As described, the moving crab-like insects are visible with the aid of a simple magnifier. The blue spots or maculae cerulae are caused by intradermal haemorrhage from louse bites. The itching is caused by delayed-type hypersensitivity to the saliva and may take 2–6 weeks to develop.

Treatment is with topical permethrin or malathion. This does not kill the eggs, so treatment is repeated after 10 days to kill newly-hatched survivors. Bedding and clothing should be washed at high temperature. His partner and other recent sexual contacts should also be treated, although Daniel alluded to the difficulties with contract tracing when people use an anonymised app to hook up.

I was interested to hear about Daniel’s forthcoming visit to the global health programme in Glasgow. I go up there a few times a year for an exam committee at the Royal College of Physicians and Surgeons. I don’t think I’ll be in Glasgow in January but if he becomes a regular visitor, our paths might cross IRL.

I already have the hardback 6th edition – gratefully received – so please leave me out of the prize draw.

As ever, thanks for an unmissable podcast.


London, UK

Trudy writes

Dear TWiPers,

The guy from TWiP 153 has a crab louse infestation caused by Phthirus pubis. Crab lice are most frequently transmitted by sexual contact. They are known for causing intense itching and producing the characteristic blue spots identified by the patient.

The infestation can be treated with both over-the-counter and prescription medications. Common over-the-counter medications include a louse-killing lotion containing 1% permethrin or a mousse containing pyrethrins and piperonyl butoxide. A second round of treatment is recommended within the following seven to ten days to kill newly hatched nymphs.

To prevent re-infestation it is usually recommended to wash clothing and bedding followed by drying at high heat. Shaving pubic hair may help as well.

Lastly, I would particularly recommend staying away from person who caused infestation to begin with. Monogamy may reduce risk, too. Just a thought.

Kind Regards,


Octávio writes:

Dear L3

The symptoms and signals manifested by the man described in last case should be caused by an infestation of Crab Louse, Phthirus pubis. In Portugal we call those “Chatos” (pronunciation CHÁ, as in “Hugo Chavez” + TOS as in “Risottos“). “Chatos” can be translated as “someone or something immensely annoying”.

Pubic pediculosis is usually sexually transmitted but can occur after contact with fomites such as clothing, bedding and towels used by an infested person.

Treatment can be performed by:

Oral dose of Ivermectin

Topical application of Lindane or Permethrin.

In Portugal topical products with Permethrin are no longer available for Human use, therefore the affected have to choose one of several over-the-counter products for head and body louse containing Dimeticone, a kind of “glue” that covers and dessicate the parasite.

In my work as a trainer for pets ectoparasitic products I learned that in some places Fipronil Sprays (for treatment of fleas or ticks in dogs and cats) are very popular for the resolution of this kind of problem. Users only complain a little because the spray’s alcoholic solution “burns a little bit”, probably because the skin is more or less severely scratched, due to the intense itching.

Thank you very much for your invaluable service teaching, informing and spreading the words of Science, please, please carry on.



Alice writes:

Hello TWIP team!

Imagine my delight upon returning from Canada to find my signed copy of PD6 on my desk! Thank you very much for this beautiful book, which I will reference here for my guess for TWIP #153’s case study.

I’m originally from Maryland, and we have a notorious t-shirt that says “We Have Crabs.” Well, perhaps this gentleman should procure one of these t-shirts for himself, since I’m pretty sure he does, in fact, have crabs. Phthirus pubis, to be exact, obtained through sexual contact while in the city. According to pages 472 of PD6, crab lice produce characteristic blue spots, which are noted on this patient. Besides the intense itching and visualization of the “papillon d’amour” with a magnifying glass, the patient is otherwise healthy. Treatment is topical insecticide in the form of a lotion, cream, or shampoo. For crab lice specifically, PD6 mentions applying pediculicide and repeating after 10 days, as well as frequent clothing washes and changes. Dry-cleaning bedding is also recommended.

Cloudy and rainy here in Syracuse today with a cool 18.9C. I’m looking forward to more TWIP episodes, especially now that I have such a great reference to use for the case studies!


Alice Wood Fox

Senior Research Support Specialist


Syracuse, NY 13210

Kevin writes:

Chicago Weather: wettest May on record, or near enough. Illinois reports its first West Nile case.

The subacute course (a few weeks) and largely external nature of the symptoms should restrict our speculations to skin conditions, dispensing with lengthy differential diagnoses that would include skin manifestations of systemic illness. The patient has not had any woodland exposures, having confined his activities to cosmopolitan locations. The presence of ‘blue spots’, also known as  sky-blue spots or maculae ceruleae (a further note on this below), inexorably drag us into the lair of the crab louse (Phthirus pubis), also formerly known as Phthirus inguinalis. The generic name is derived from the Greek theiriasis-to be infested with lice. A quaint description of this pest is seen in John Stephenson’s 1831 Medical Zoology, “This disgusting parasite inhabits the eye-brows, pubes, &c. of men and women….it is a frequent cause of local prurigo…”

A less direct and more Victorian description was found in an 1867 English encyclopedia where the pubes are only suggested by a prim ‘et cetera’ :

“and lastly, the P. pubis of Linnaeus, which constitutes Leach’s genus Phthirus. This species inhabits the eyebrows, etc, and is commonly known by the name Crab-louse.”

The crab louse is about 1mm long, very dorso-ventrally flattened and rather translucent in appearance, making initial detection a bit difficult. This obligate blood sucker keeps a tight grip on the hairs and lives closely adhered to the skin, which can mimic a small scab or excoriation. The pubic hair, male escutcheon, eyebrows and eyelashes are common habitats, but many other hairy areas can be incidentally infected. I’ve seen them on the ventral aspect of the forearm. A reference is appended that describes a scalp infestation. Transmission is almost universally person to person via intimate contact, but some wiggle room is afforded to afflicted partners in monogamous relationships by rare reports of transmission by fomites. I was amused to see that PD6 still invokes the legendary ‘toilet seat defense’ as a mode of transmission. I will suggest that the conventional smooth plastic toilet seat is a very unlikely launching pad for the clumsy wingless louse. However, in defense of PD6 (a lovely book which I consult frequently) I have appended a photograph of a plush fabric toilet seat that might answer to the needs of a wandering crab.

Crabs reproduce on the host and lay their nits (eggs) on the hair shaft. According to Nuttall (1917), the nits of Pediculus (body and head lice) differ from the Phthirus nits, but this is only of academic interest. (illustration provided).

Unlike the human body louse (Pediculus humanus) which can transmit Rickettsia prowazekii (epidemic typhus), Bartonella quintana (trench fever), and Borrelia recurrentis (relapsing fever), the crab louse transmits no known illness. In the early days of the HIV epidemic there was a great deal of interest in the theoretical transmission of HIV from human ectoparasites (lice and bed bugs), and other blood-sucking insects. Some of the early speculations and research on this fear can be seen in the 1987 Office of Technology Assessment monograph,” Do Insects Transmit AIDS?”

Treatment in the early 1800s might include mercuric oxides. Fortunately now one can go to the local pharmacy and pick up the 70s favorite A-200 (piperonyl butoxide and pyrethrins) or RID. These agents are not ovocidal and so require retreatment in 7-10 days. Scrupulous adherence to package directions is essential for complete cure. Eyelash infestations managed by manual removal of the insects or the use of ophthalmic grade petrolatum ointment applied 2-4 times a day for 10 days. Everyone seems to love ivermectin, but 4 ounce tube of the topical form costs $280.

I would like to close with a note on the curious blue spots, a phenomenon that I first heard of on TWiP 153. A fascinating article in the journal Parasitology (March 1924) : Maculae coeruleae and Phthirus pubis. The microdissestions of crabs and bizzare human experimentation (presumably done on Russian military recruits) are a glimpse into medicine’s sordid past. A quote from the article:

“The blue spots induced by the bites of Phthirus pubis in man’s skin are due to the action of a ferment emanating from the bean-shaped salivary glands of the insects. This ferment acts apparently upon the haemoglobin which, becoming discoloured, causes diffuse bluish coloration of the skin to appear in situations where the insect injects its saliva.”

Thanking you all for your sublime educational service.


Medical zoology, and mineralogy; or Illustrations and descriptions of the animals and minerals employed in medicine, and of the preparations derived from them: including also an account of animal and mineral poisons. 1831, John Stephenson

Charles Knight’s 1867 Natural History: Or, Second Division of “The English Encyclopedia”, Volume 4

Sept 1987, from the Office of Technology Assessment, Do Insects Transmit AIDS?

Scalp Infestation With Phthirus pubis Robert J. Signore, DO; John Love, MD; Michael C. Boucree, MD, MPH Arch Dermatol. 1989;125(1):133. doi:10.1001/archderm.1989.01670130135025

Maculae coeruleae and Phthirus pubis E. N. PAVLOVSKY, M.D., A. K. STEIN, M.D., Clinical Assistant in Dermatology and Syphilis,

Military-Medical Academy, Petrograd Parasitology Volume 16, March 1924 , pp. 145-149


Plush toilet seat:

plush toilet seat

Nutall, Comparison of Pediculus and Phthirus ova

Lauren writes:

Hello TWIP

Case study for episode 153 “Gentlemen from the clinic.” My diagnosis is Phthirus pubis, (pubic lice or crabs); “The usual characteristic of infestation by all types of lice is intense itching. Constant scratching can lead to secondary bacterial infection of the wound. Crab lice produce characteristic “blue spots””. Parasitic Diseases, 6th Edition

Diagnosis depends on identification of lice or eggs, Eggs must be identified by microscopy. But it sounds like you got a positive ID of the lice.

Treatment may be hard and tedious do too the risk of re-infestation. when speaking with the gentlemen stress the importance of informing and treating the domestic partner as well. Simply washing affected areas with soap does not kill lice or nits (eggs).

All current sexual partners and subsequent partners of both gentlemen from clinic and his domestic partner must follow regiment of treatment or be excluded from sexual encounters due too the risk of re-infestation during infection. May be easier to treat if closed relationship during infection.


  • Over-the-counter treatment or prescription of shampoos, lotions, and creams with low concentrations of insecticides permethrin and Benzene hexachloride
  • All bedding, towel, clothing must be washed and dried on a hot cycle daily and clothing should be exchanged for clean clothing after every application. All daily grooming equipment needs to be heat treated to 70 or 158 for 30 mins for best results.
  • Nit comb (combs with closely spaced teeth to scrape nits)

Eyebrows and beard needs to be examined for pubic lice if found a thick layer of petroleum jelly will bring the lice to the surface and then must be pulled out with tweezers, do not use insecticide on the face.

I recommend for our gentlemen nit combing, Oral ivermectin and or Benzene hexachloride (lindane, Kwell) for second line therapy due to persistence of lice. And concerns regarding benzene hexachloride toxicity.  For his domestic partner permethrin 1% is recommended and nit combing. Gentleman and his partner could treat each other. Allowing for more accurate treatment. It is important to be thorough because most treatments do not affect eggs pubic lice can produce 30-50 eggs. The egg stage lasting around 10 days. With a lifespan of 3-4 weeks. Adults need a daily blood meal. Nits do not until they are newly hatched. Goal is to disrupt the lifecycle of the pubic lice before they can lay eggs.

Bedside manner is also important so he does not feel embarrassed and hopefully will come in for treatment for STI’s earlier next time. I know you guys are truly caring doctors thank you for taking time for making TWIP.


Cullen writes:

Hey twipers,

My guess for the man with an itching pubis and umbilicus is Phthirus pubis (common name: crab louse). Given the distinct wounds and constant itching, I would say these bugs are living at the base of his pubic hairs and consuming their blood meal causing small wounds that can be bluish in color. As always, thank you for a fun podcast I can listen to while pipetting and plating.



Atlanta, GA

Lawrence writes:

Dear TWiP team,

I’m a regular listener, but unfortunately I’m typically several weeks behind on listening to my podcasts, so unable to venture a guess case study.

I had a more general question that I hope you can help with: how do you stay current with the literature?

I subscribe to newsletters from a handful of journals and organizations, but I imagine that there is a lot of research that is not covered in these sources. Is there something like an ‘infectious disease digest’ that summarizes recent research? I’ve tried searching with Google for something similar but to no luck. How do you stay on top of current research? I enjoy listening to the TWiX podcasts, but hope there might be a regular publication that highlights notable research and advances in the field (which might also include things outside peer-reviewed publications).

All the best,


Anthony writes:

Cannibalism was far from unknown in our species’ history. Through this route, polio in the CNS would not be a dead end.  Polio disabling a host that’d then be easy prey would encourage transmission.

Baylisascaris larva migrans cripples small birds and mammals and so makes it easy for raccoons to catch them.  Might polio have so helped its favored hominids to have their neighbors for dinner?


Noah writes:

Dear TWiP Team,

This page (533, see attached) of Parasitic Diseases is inexplicably confused about the singular “nucleus” and plural “nuclei”. There must have been some sleepy copy-pasting.

Yours, Noah

Andrea writes:

Hello Again Twipitos!

This must have been my month to find these articles, have you seen this one?

I am guessing that this is pretty common but since I’ve been listening to your podcast I now find these kinds of situations fascinating and repulsive at the same time.

What can I say we grow them, that is me, weird up here in the Northwest where it is 43F at 1 AM and no rain but it is cloudy, of course, so we in Seattle missed the Super/Blue Moon.

Courtney writes:

Dear Professors,

Greetings from Omaha, Nebraska. It is ~32 Fahrenheit and nice enough to wear just a sweater.

I hail from University of Nebraska- Omaha where I am a master’s student. My research involves bee and if they prefer a homogeneously managed or patchily managed landscape. I’ve been a listener for over a year but this is my first time emailing into TWIP.

On one of your most recent podcasts (either 146 or 145) you spoke about polyploidy and it’s prevalence. I thought I would point out that plants can get all sorts of freaky with their genetics and many times have much more than two or three chromosomes. For instance Celosia argentea and Spartina angelica have 12!

Fun fact: platypi (or is it platypuses?) have 10 sex chromosomes.

On to my first ever guess. My method of narrowing down possibilities was opening your lovely book and ctrl+f’ing “ulcer”. The first thing to pop up was Cutaneous Leishmaniasis. Reading the description it fit it quite well, however it is always best to double check. Going through the “ulcer” list, it seems most of them were internal ulcers or cause diarrhea. None of which describes our patient. Acathamoeba was a possibility, but the immune systems seems to be “ok” and the ulcer wasn’t near the eye. The last remaining two were Dracunculus medinensis aka guinea worm, but our patient is not from one of the four countries it is currently residing. Lastly, tularemia was an option, but there wasn’t any myalgia, fever, or enlargement of lymphs.

I would really like it if you did do arthropod and fungal parasites.  It would also be nice sometime to hear more papers about those things and not just from a molecular side.

Thanks for the wonderful podcast,

Luke writes:

Dear all,

I’m a first-time listener recently introduced by one of my friends, studying biology at Aberystwyth University in Wales.

I first thought of Guinea-worm (Dracunculiasis), primarily due to the presentation on the foot and the waterborne nature of the GWD (as the rafting seemed key). After checking symptoms, distribution and images, it doesn’t seem to match up. GWD is restricted to Africa and India, where the patient had only been South America. GWD is also noted as having a range of symptoms, such as fever and inflammation on infection, and allergic responses later due to responses to worm secretions, which the patient surely would’ve noted. The key here is that the blister/ulcer formed would be painful and would not have the white fibrous coating et cetera noted in the clinical inspection. It’s noted in the book that GWD may seem like some dermatological conditions, seeing as this is “This Week in Parasitism” not “This Week in Dermatological Conditions”, we can discount this.

My friend pointed out cutaneous leishmaniasis, which seems to fit the bill much more closely. Firstly, the non-tender lesion with a white fibrous coating is key to the diagnosis, it’s the only non-tender ulcer noted in the book. The time scale also matches better to CL than to GWD, as GWD takes over a year to present with an ulcer, while CL would present within a month, as the patient said. Leishmaniasis is also common in South America, Costa Rica is noted for tourists especially ( Cutaneous leishmaniasis does not often present on the foot, but as was noted in the notes, if the patient wore sandals extensively, and was bitten there, it’s possible that CL could show here.

Ultimately, the deciding factor for me was that Dr. Despommier seemed to get the diagnosis straight away. Problem solved.

I’ve really enjoyed the show so far, listening to the back-log of episodes as I work. All the best,

Luke, Aberystwyth, Wales.

Steve writes:

Could be one for Daniel. 🙂

Keep them coming. (y)

Steve Hawkins




Weather pleasantly warm and sunny…

Maureen writes:

Interesting cattle worm parasite case you might want to discuss:

Worm in woman’s eye leads to unique discovery

Ted writes:

Hi TWIPers,

I came across this article that I thought might make a neat case study on an upcoming TWIP.


Ted Diehl

William Diehl

Postdoctoral Fellow

Program in Molecular Medicine

Mass Medical School

Eric writes:

Hello again,

From the description of a chronic, painless ulcer with a raised edge originating from a papule, I think our patient has cutaneous leishmaniasis.

Before hearing of a trip to Costa Rica, I first thought of diabetic foot ulcers. However, they usually are purulent and on the bottom of the foot, and late complications of diabetes are unusual in an otherwise healthy young man.

Actually, the very first thought that flitted through my imagination was Buruli ulcer, because it is a neglected tropical disease. Buruli ulcer is caused by a prokaryote (Mycobacterium ulcerans) and is endemic in Central Africa, not Costa Rica.

I searched PubMed to help me guess which of the 15 New World species listed in your textbook were found in Costa Rica specifically. In this review by a familiar author*, I found that L. panamensis, braziliensis, and infantum can be found west of Panama, with L. panamensis the most commonly seen clinically in Panama. I also found some similar case reports from Costa Rica that were L. panamensis. In these reports, PCR was used to identify the species. Don’t know if the species identity was needed for this case, but I’m interested to find out!

*Hotez PJ, Woc-Colburn L, Bottazzi ME. Neglected tropical diseases in Central America and Panama: Review of their prevalence, populations at risk and impact on regional development. International Journal for Parasitology. 2014;44(9):597-603. doi:10.1016/j.ijpara.2014.04.001

Thanks again for the podcast!


Los Angeles

Lana writes:

Dear Leishmanics,

I’m a longtime fan, but only an armchair biologist. Therefore this reply is not intended to be a substitute for professional medical advice, diagnosis, or treatment. I want a signed book, though, so here goes!

The painless ulcer on the foot of the recent Costa Rica visitor is likely New World cutaneous leishmaniasis. The infection is caused by a protozoan parasite and is transmitted through the bite of an infected sandfly.

The various strains and clinical manifestations of leishmaniasis respond best to different treatments, so the strain of the infection should be determined whenever possible. In Costa Rica, Leishmania (Viannia) panamensis is the most common strain, but other strains have been isolated there as well.

Treatment choices are complicated, but I found a few possibilities. Some of the more effective treatments carry a risk of systemic toxicity and many of them aren’t available in the U.S., so that simplifies the task somewhat.

Since the patient only has one lesion, if mucosal involvement is judged to be unlikely, local therapy may be preferred. This might include cryotherapy or thermotheraoy. Topical paromomycin cream also looks promising, but may not be available in the U.S. According to the CDC’s website, it might be available through a compounding pharmacy or could possibly be imported under a single-use treatment protocol. For systemic treatment, pentavalent antimonials have traditionally been the go-to therapies, but the only one that is currently available in the U.S. is sodium stibogluconate, which has many toxic side effects. The oral medication miltefosine has been shown to be effective against most strains found in Costa Rica, so it might be an alternative worth considering.

Thank you for all of the great work you do on the podcast and around the world.

Allan writes:

Greeting Professors TWIP,

My guess for the patient with the lingering painless ulcer and river exposure in Costa Rica would be cutaneous leishmaniasis transmitted by a sand fly.

Have been teaching in SE Nepal for 3 weeks (and introducing medical students to your excellent online Parasitic Diseases 6th Ed) and was just talking with a local physician about the the low but persistent prevalence of cutaneous leishmaniasis both in Nepal and in the refugees here from Bhutan. You podcast seemed like a timely reminder that this infection is still around places beyond just Afghanistan. Hope this gets in before your next segment.

Keep up the great work.


Allan Robbins,

University of the Nations

Global Health


Anthony writes:

The Black Rat (Rattus rattus) originated in India, but spread throughout Europe. The fleas that live on the Black Rat are thought to have transmitted the Plague to people in Europe during the Middle Ages.  The Brown Rat (Rattus norvegicus) came from Asia and generally replaced the Black Rat in Europe. The observation/speculation is that the flea of the Brown Rat is species specific and this limits the spread of the Plague.  

The Black Rat came to the West Coast of the US on ships from China.  The Black Rat is thought to have brought the Plague to San Francisco in 1900.  

Here’s an interesting article on the Plague in San Francisco, though not focusing on rats:

The Black Rat is thought to be responsible for the introduction of Plague to Prairie Dogs.  


# # #

Whitney writes:

Greetings Dear TWIP Trio,

I found this paper today published in Scientific Reports by a group of researchers from the University of Notre Dame about how dominance rank of animals might affect parasite risk:

I thought that this might be an interesting paper to discuss on your podcast as I also study parasites in a vertebrate animal system and have recently become interested in how parasitic infection connects to animal behavior.

It is presently 54 degrees Fahrenheit in College Station, Texas and partly cloudy.



Steve writes:

Hi Twipsters,

Just a quick heads up about Nature’s ‘Scitable’, which I’ve not seen before. Here, with some nice graphics, is the story of the discovery of the apicoplast.

Listening to TWiP, I hadn’t looked at the diagrams before, and had not realised that the apicomplex was separate from the apicoplast. (From the name, it sounds like they’d both be together at the apex–which is a bit misleading.).

The Scitable piece was linked from another piece in ‘The Conversation‘ , by Lilach Sheiner of Glasgow University, on the discovery of a possible new approach to tackling Toxoplasma gondii:

Direct link to pdf of the Wellcome comic:

All the best,

Steve Hawkins



Where it is trying to be Winter again.

Anthony writes:

Perhaps this rates a mention:

Rich writes:

Excuse the terseness, but just saw this on the MIT news page and wanted to be sure you’d seen it. Seems like a truly monumental advance in the study (and hopeful irradication) of Malaria!

Human malaria parasites grown for the first time in dormant form

The weather here in Boston is, well, still too damn cold!

Thanx for all your hard work helping to make science more accessible to the rest of us humans! Even computer geeks like me can understand at least some of what y’all talk about!  Your shows are fun, engaging, and I think I’m actually learning something about biology!

Take care all!

— Rich

Lindsey writes:

Dear Triasites,  

I am a mechanical engineer who has used the back catalog of Twip for several road trips.

I am also a regular listener to Twievo and Twim.

Fortunately, I know some microbiologists and entomologists that I have put onto Twip.

I suspect that I am the only mechanical engineer with a copy of Parasitic Diseases 6th on my phone.

The only case study that I have been able to get was when Daniel snuck in the Recluse case.

And this is only from having watched a bite point grow on the inside of my left elbow.

The only problem that I have had in discussing the twip podcast is that my wife has forbidden it during mealtimes, I’m not exactly sure why.

With the book, I’ll start more serious attempts on the case studies.

Keep up the good work.

All the best.


BTW, at Texas A&M University, high today 80F

Two weeks ago in Big Bend, had 3 days bumping 90F

David writes:

Dear and esteemed parasitism panelists,

It is Wednesday evening and I suspect the case is due for tomorrow – although sometimes the intervals vary.

Initially I thought that the sick boy with the distented belly and the occasional cough had an ascaris lumbricoides infection. But that did not seem to explain the pale character, low weight and lack of responsiveness.  A hookworm infection would be rather in line with these symptoms. I browsed our beloved handbook for quite a while on the various symptoms – the lack of teeth and dry skin seemed to suggest something else still.

In the end, although I am probably wrong, I would guess it’s a coinfection of both ascaris and hookworm.  Both are common and are associated with dirt floors. I guess the combination of the two might well lead to fever, thus dehydrating the child without diarrhea.

It’s better to have played and lost than to not have played at all, so for this case this is my humble guess.

Yours sincerely from Jinotepe,