Jason writes:

Hi Vincent and Dick.  My name is Jason Rohr and I study various parasites of humans and wildlife.  I just wanted to thank you for covering our recently published work on This Week in Parasitism (Halstead et al. 2018. Agrochemicals increase risk of human schistosomiasis by supporting higher densities of intermediate hosts. Nat. Comm.  9, Article number: 837). It was great – a lot of fun to listen to! And, Dick, we will be sure to mention vertical farming as a viable option for increasing food production and reducing the adverse of effects of agrochemicals in the future;)  Thanks again!


Jason R. Rohr, Ph.D.


University of South Florida

Jani writes:

Hello TWiPsters,

I’m a long time TWiX listener, first time writer.

In TWiP 149 professor Racaniello said that every virus that gets in the CNS is a mistake.

Seems to me that the rabies virus benefits from being in the CNS. The violent movements, uncontrolled excitement, confusion, and other behavior changes caused by the inflammation of the brain make the infected animal more likely to bite and infect other animals.

Hydrophobia prevents diluting the viral load in saliva. I assume the hydrophobia is also at least partially caused by the brain inflammation.

Jani (pronounced YAH-nee), a software developer from Finland

Rebecca writes:

Dear TWIP friends

I have been enjoying your podcast for many months now, even though I have no medical knowledge. In fact, I like to tell people that I am the wrong kind of Doctor – rather fewer people have the need for an ecologist than an MD. This doesn’t prevent my enjoyment of the podcast, as the diagnosis and treatment of parasites is as fascinating as their ecology.

I was very interested to hear the discussion in Episode 149 about the use of agrochemicals. I felt that I couldn’t let one assertion go unchallenged – that commercial farmers care only about profit. Have you ever known someone go into farming because they think it is a lucrative business? My experience is that they farm despite the level of profit rather than because of it.

Agrochemicals are used for many reasons, and profit is just one of them. One factor is that people like you and me choose and expect cheap food, and as a society we also don’t currently possess the knowledge and technology to feed the global population without the use of chemicals. If we want to change this, we all have the power to choose more sustainable diets. I therefore prefer that we first take a look at our own behaviour before putting all the blame on others.

You seem very knowledgeable about topics related to food production, so I am sure that you are aware of the land sharing vs land sparing debate. Your listeners, however, may not be, and I think it is an important one to be familiar with when discussing the use of agrochemicals. I’m therefore sharing a link they may enjoy: https://youtu.be/zTVC32Bfl-U. The challenge of building a sustainable food system is extremely complex and I am pleased to see it explored.

I look forward to future episodes, and hope to hear more about your sailing adventures as well.

Best wishes,


Case guesses:

David P. writes:

Dear Hosts,

I believe the 31-year-old man from Panama suffering from an ulcer on his leg has contracted a case of cutaneous leishmaniasis from the protozoan parasite Leishmania braziliensis or L. panamanensis. The man likely contracted this parasite from a local sandfly in his outdoor work in the field. The slow growth rate of the ulcerated lesion from a small papular bump to its current size of 4 cm over a month fits the diagnosis quite nicely, and Daniel’s description of the dermoscopic features of the lesion helped seal the diagnosis. Upon Googling the features of a cutaneous ulcer, I came across a paper that described this patient’s results to a word: “erythematous papular initial lesion” and “yellow tears”.

Thank you once again for the informative and entertaining podcasts.


David P.

Peter writes:

A cháirde TWIP,

If you would like some pointers in the pronunciation of “A cháirde”, your former president had a good go, as seen in this video recorded outside our university at about 2m16s.

To investigate this case study I was joined by Gwen Deslyper and Rachel Byrne.

Is Dr. Griffin trying to trick us? This was our first thoughts after hearing the case study. It definitely sounded like Cutaneous Leishmania, which was also the correct diagnosis of a very recent case study on TWIP. The literature we consult has now benefited from the addition of “Forgotten people, forgotten diseases” by Peter Hotez, which I was lucky to win from TWIV (Thanks again). Consulting that, we read the early stages of Cutaneous Leishmania resemble those of Buruli ulcers. Parasitic Diseases 6th edition also warns about confusion with leprosy. However, the small yellowish teardrops, as well as the white starbursts, appear more consistent with Cutaneous Leishmania, for example in this 2017 paper. Panama and insects bites also agree with Leishmania. So with some hesitancy we will go with Cutaneous Leishmania again. To confirm it is Leishmania and identify it to species level we would carry out PCR. Also important as treatment will be species dependent, as some species in Latin America may spread to the mucus membrane. When you last spoke of Leishmania you spoke of the stigma associated with CL infection. Hotez’s book contains the line “For instance in Afghanistan, even though CL is not transmitted by contact between people (it requires the sandfly vector), mothers with CL are prevented from touching their children”. How terribly sad and unnecessarily cruel. Highlights the importance of educational tools like TWIP.


Peter Stuart,


Chris writes:

Hello hosts,

This week was a nice and easy one so I didn’t feel the need to look up the symptoms for the answer.  I believe the man has cutaneous leishmaniasis based of the symptoms. Also once Daniel mention the yellow teardrop I became curios and Googled that and and found that it occurs in 41.7% of dermoscopic examinations and the white starbusts appear 60.4% of the time. Lastly it is a sunny 37° F here central jersey with rain scheduled for this week.

Warm regards from an aspiring parasitologist ,


Eric writes:

Dear TWiP hosts,

From what I learned in episode 147, I believe that Dr. Griffin’s patient has cutaneous leishmaniasis.

This review reports that Leishmania panamensis is the most prevalent species in Panama, as its name suggests*, and I’m guessing the patient acquired this species. I’m interested to hear about how this case was managed.

The teardrops and starbursts Dr. Griffin saw with his dermoscope sounded at first pass like the organisms or something they secrete. I was probably thinking about Leishman-Donovan bodies, but now I know that a dermoscope doesn’t magnify to the level of single cells. A quick search yielded me at least three case series of Old World cutaneous leishmaniasis — from Spain, Iran, and Turkey — describing these phenomena as areas of rapidly proliferating host skin cells.



David Geffen School of Medicine at UCLA

*One cannot assume a species’ scientific name is meaningful. There are many cases where the author of a new species used the wrong location to create the species’ scientific name. Furthermore, taxonomic rules prohibit changing a scientific name once published to avoid confusion. Only when someone finds a scientific reason to redefine the species can names be reassigned.

Random example: The mussel species Isognomon californicum (Conrad, 1837) is only found in Hawaii, but the species name has been around since 1837, I surmise.


Hotez et al.  https://doi.org/10.1016/j.ijpara.2014.04.001

Llambrich et al.  https://doi.org/10.1111/j.1365-2133.2008.08986.x

Taheri et al.  https://doi.org/10.1111/ijd.12114

Yücel et al.  https://doi.org/10.1111/j.1365-4632.2012.05815.x

Suellen writes:

First, let me tell you how super-happy I was that when I heard this case, I actually was immediately able to come up with a diagnosis in my head, without referring to Parasitic Diseases 6th Edition OR Dr. Google. That means that I am actually retaining some of the great material I get from TWIP.

My top-of-mind diagnosis was Cutaneous Leishmaniasis, because I remembered that it causes a lesion of the size mentioned in the case. But I also remember that this was the diagnosis for a case just a couple of episodes ago. Still, it seemed to fit the facts of the case, and although I did search both PD6 and Dr. Google, I was not able to find another parasitic disease that fit the case so well.

Other possibilities that I researched:

Guinea worm — while this does cause an ulcer on the foot, it is now both very rare and confined to a few countries in Africa. So not a good candidate

Toxicara — this produces those “serpiginous” lesions, which this patient does not have

So in the end I decided to go with CL, because it seems to fit the case best.

Lauren writes:

Dear Vincent and TWIP crew

Thank you for your enthusiasm to share science.  

Case Study for TWiP 149

31-year-old man with ulcer on his leg.

My guess is; cutaneous leishmania, panamensis (Mid stage).

This is based on, that it sounds like the case study for twip 146 of the 27 year old lawyer with ulcer from New York.

And Daniel is now back from Panama . Mid stage; because yellow droplets are early stage and white starbursts are late stage.

Sorry I did not have a well written out diagnostic or treatment to suggest at this time. I just wanted to participate in The case study.

Lauren from Sunny San Diego.

Patricio writes:


Based on the description of the ulcer and the place of living, I presume it is a case of cutaneous leishmaniasis.



Alice writes:

Greetings Doctors of TWIP!

My name is K. Alice Fox, and I am a Lab Manager/Technician to a Fish and Wildlife Disease Genetics lab at SUNY-ESF in Syracuse, NY. I have been listening to your podcasts since last September when I took a Parasitology course to learn more about the parasites I am working on in the lab (my background is actually plants, so this was new and fascinating territory for me!). I am finally all caught up with the podcasts, which I have been voraciously devouring during many long hours of running PCR, DNA sequencing, and bacterial cloning of various wildlife and their assorted parasites. Now that I am all caught up, I thought I’d give my diagnosis for #149’s case of the 31-year-Northern Panamanian with…..Leishmania!

This otherwise healthy man presents with a 4cm painless, reddish, raised-bordered leg ulcer that developed from a smaller papule over the course of a month. Given: his location, outdoor vocation, the lesion’s raised border and slow growth rate; the fact that it’s painless and he’s otherwise asymptomatic, I’m going to go with cutaneous leishmaniasis. Leishmania is a protozoan parasite that is transmitted through infected female sandfly bites.

Cutaneous leishmaniasis is the most commonly presented form characterized by skin lesions that develop over several weeks or months. The sores are usually painless (unless they become infected with bacteria) and take a long time to heal. Given he is in Northern Panama near Costa Rica, this is a New World Species of Leishmania of either the L. mexicana or L. braziliensis species complex. Diagnosis is by microscopy of skin lesion samples; PCR could also be run to determine the species.

Treatment depends on several factors, including species, geographic area, and the lesion progression. In general, healing the lesion is key. Cryotherapy, thermotherapy, and topical application of paromomycin are suggested on the CDC page. Systemically speaking, there are a few options for the New World Leishmania including Pentostam, Amphotericin, Miltefosine (listed to be effective against three New World species), and the “azoles” (ketoconazole, fluconazole) which have had mixed results but could work for our Panamanian with Leishmania.

I have really enjoyed exploring this fascinating field through your podcasts, and look forward to hearing your voices through my earbuds during many more hours of running PCR!



Alice Wood Fox

Senior Research Support Specialist


Rhonda writes:

Greetings to all the Twip team! My name is Rhonda and I work in a clinical microbiology lab in Washington State. I think cutaneous Leishmaniasis is likely the cause of this patient’s ulcers. The description of a bump escalating into an ulceration with raised hard borders fits in with the typical presentation, along with an absence of pain. Also, Central America is an endemic region containing Leishmania. The dermoscopic exam also seems to fit the picture of cutaneous Leishmaniasis although I must admit I had to consult google. I have just recently discovered your podcast and have been working my way through the backlog. Keep up the good work, I hope you never stop.

Elliott writes:

Stranger in a Strange Land

     T.W.I.P case #149

Hi, my name is Elliot I am an avid listener to T.W.I.P, T.W.I.V as well as T.W.I.M. I am a current student with double major epidemiology and bio-chem. I decided to do some research on this young man in northern Panama on the border with costa rica. I am going to hazard a guess that the diagnosis of hookworms specifically anclylostoma or duodenale family. The man is 31 years old who works with sugar cane an extremely dangerous profession. Now the ulcer could have aroused from a laceration from the equipment used in cutting the cane. however I remember how you stated that it started as a small papule which could be the penetration site of the hookworm. Most likely he picked it up from kneeling in tainted soil that they were using to fertilize the cane fields without proper ways of purifying the soil. The light smoking and drinking could have helped break down his immune system and allowed the small papule to turn into a fully ulcer. The redness around the wound could be early signs of infection of blood poisoning due to lack of proper sanitary conditions, which explains why his blood pressure is slightly elevated, this also points to the arrhythmia. Now for the blood smear showed signs of yellow teardrops could have been the pockets of live larvae before they burrowed into the bloodstream eventually ending up in the intestinal tract, if I was the physician I would have ran a stool sample however in a village like this it may not have been possible so I would try a 3 day dose of the antihelminthic drug family as these are relatively harmless and are very effective most often. Depending on iron levels or the presentation of any anemia I would also prescribe a months worth of iron supplements as well. I will keep trying different cases because I find these subjects extremely satisfying to the brain and my favorite thing to study thank you guys very much and have an awesome week  

Dylan writes:

G’day TWiPers,

Hopefully im not too late! My name is Dylan and I am currently finishing off my last semester of my Undergrad at the University of Queensland, hopefully going on to study parasitology in my honours!  I’m a recent listener to TWiP and the podcasts are so enjoyable to listen to on my daily train rides.

In terms of the case study for TWiP 149 my guess is Leishmaniasis, more specifically cutaneous Leishmaniasis. When the ulcer on the leg was mentioned in instantly thought of a Diptera vector, and googled to see what was found in Panama. Quite a few articles came up with Sandflies being quite prominent, and since they are a well known vector of Leishmania i instantly jumped on that. Looking further into the symptoms, I found that Erythema is always found with cutaneous Leishmaniasis, while teardrop structures and white-starburst patterns are found in 42% and 8.6% of dermoscopic examinations respectively. These findings really support my idea of the parasitic infection being a Leishmania protozoa!

Keep up the great and super interesting podcasts!



Konrad writes:

Dear TWiP team,

I’m a new listener, an undergraduate interested in global health, and am looking forward to going through the TWiP and other backlogs. I want to jump right in with an attempt at the case diagnosis for the March episode — hoping this email doesn’t come too late.

The patient is in generally good health, suggesting that the ulcer is not a sign of immunodeficiency or of a systemic infection. The ulcer also is painless, has no scab, and developed over time from a small bump or nodule. That is characteristic of localized cutaneous leishmaniasis, caused by protozoans of genus Leishmania, which are endemic throughout much of South and Central America, Asia, and Africa.

The size of the ulcer is within the expected size range for cutaneous leishmaniasis, and although I have no dermatology/pathology knowledge, the redness, starburst patterns, and teardrop-like structures observed on dermoscopy match known dermoscopic features of cutaneous leishmaniasis (Llambrich et al 2009). Phlebotomine sand flies transmit the parasite to the definitive host (human or other vertebrate). The patient works in the field, so he may well have encountered the sand fly on the job; since his home is exposed to the air, he may also have been exposed while sleeping.

Unlike more severe forms of leishmaniasis (most notably visceral), the patient shouldn’t be in serious danger. The ulcer should heal by itself after some time. Antiparasitic medications that are effective against leishmaniasis often are toxic; if the ulcer isn’t causing serious distress, monitoring with no active treatment may be the best option.

Thank you for the educational and engaging podcast,

Konrad Fondrie

University of Wisconsin Oshkosh
Paper used – Clinical and dermoscopic evaluation of cutaneous leishmaniasis (https://www.ncbi.nlm.nih.gov/pubmed/25208634)