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TWiP 76 letters

Daniel writes:

Dear Vincent and Dickson,

I just returned from the annual meeting of the International Society of Travel Medicine (ISTM) where I enjoyed many fantastic lectures and caught more Cutthroat Trout fly fishing the upper Snake River during one evening than I could count. I will confess to using a hopper with a bead head dropper to achieve this. I was relaxing on this beautiful Sunday morning with a cup of coffee in hand and the August 1st issue of Science. To my delight I saw that the cover had a colorized scanning micrograph of a dog roundworm (Toxocara canis). This image on the cover directed the reader to a commentary and to two research reports about how infection with parasites influences the immune system in such a way that antiviral immunity is impaired.

I am an MD trained as an infectious disease specialist and am active in the care of immigrants, travelers and indigent patients suffering from infectious diseases. At NYU School of Medicine I received excellent training in parasitic disease from a dynamic visiting professor that has served me well in China, Africa, Nepal and here in the states. My PhD is in Immunology and my early work involved defining the phenotype of human B1 cells, an innate subset of B cells. My current work is on HIV latency in hematopoeitic stem cells. These research reports were thus as they say ‘right up my alley’. The commentary is readily accessible to a broad audience and explains how the two research reports demonstrate that helminth infections induce viral exit from a latent state. The two research reports contain the expected rigor one sees in Science.

These reports seem a perfect crossing of both your areas of focus, Vincent’s expertise in virology and Dickson’s expertise in eukaryotic parasites. Schistosoma mansoni is one of the parasites involved in the first article and one even my kids know about after swimming in Lake Malawi this past winter. Trichinella is used in the second paper and is not only dear to Dickson’s heart but something we still see up in Alaska, where I worked until recently. To fully disclose my fascination with parasites, the discussion my physician friend from Alaska and I were having as we caught cutthroat trout on the Snake last week was about the two cases of acute Trichinosis that he recently managed in a married Alaska couple from eating undercooked bear meat.

I am left thinking that Dickson needs to fish the upper Snake River in Wyoming, but more importantly he might consider writing a monograph entitled not People, Parasites & Plowshares but: Parasites: When Plowshares become Swords!


Daniel Griffin, MD PhD
Associate Research Scientist
Department of Biochemisty and Molecular BioPhysics
Columbia University

Francois writes:

Vincent, you’ve got French listeners, at least one!

I'm living in Montpellier (south of France) were the sun is shining.

Here two very visuals picks of the week.

You already know of the glass virus of Luke jerram, but here the malaria model

And also for sheer beauty ... Giant glass flower from Jason Gamrath


Robin writes:

Various items

Malaria prevalence
Can be so high that asymptomatic parasitaemia is the norm: it was 95+% among adults of some New Guinea tribes and over 70% among the adults in the territory of Anopheles gambiae.

French speakers
Among the reasons I am not a French speaker were Horatio Nelson and the Duke of Wellington, to neither of whom I have any affinity or allegiance. But they were among the reasons that the Raj was a British Raj, and not a French one. An important reason also why so many Indians (& Pakistanis) speak adequate if not good English, and little or no French.

Schizont pronunciation

Single vs multiple ring forms
Multiple rings in an RBC is bad news.

Parasites are doomed
As in the answer to the question about Bob Dole in the 1996 presidential election - "Does he wear boxers or briefs?": "Depends". Those that adapt well enough may become a necessary feature, as Dr. Dickson has explained with regard to intestinal parasites and autoimmune disorders of the gut (and perhaps elsewhere). And let's not forget the bacterium that invaded an Archean to produce the great*gazillion grandparent of all of today's eukaryotes. Mitochondria are no longer parasites.

Extra membrane protein in RBC cytoplasm
One reason for it may be to prolong the life of the RBCs. Think of a tire filled with tread that can migrate to the outside as the tread on the outside is worn away. RBCs are subject to plenty of wear as they squeeze through narrow capillaries.

Movement of Homo sapiens and other hominids outside Africa Extincted by human disease
There were two (known) non-sapiens lineages outside Africa in later times that we met: neanderthals and denisovans. We may have also met floresiensis but there is no genetic evidence for commingling. Just about all other hominid species were in Africa and were exposed to the infective load found there. Moreover, we coexisted with Neanderthals for ten millennia or more.

Within our species 14 disease-free millennia after crossing the Bering land bridge into the New World and several more disease-free millennia preceding in Siberia helped to make Native Americans susceptible to smallpox and measles, thus enabling settlement of vacated territory by Europeans who brought those diseases as naturally as their ectoparasites.

Homo habilis evolved into Neanderthal
I had the impression that it was a more advanced form: Homo heidelbergensis.

Colder climate - invasive species
The hairless ape is adapted to year-round tropical weather. Anywhere else it is an invasive species: to survive elsewhere it has a cultural/technological adaptation that proceeded much faster than evolution: shelter & clothing.

Cause of migration civil war
Not necessarily. It would be doubtful whether the migration across the Bering land bridge was due to civil war. The migration of Jews out of Europe in the time of the Third Reich was not quite due to "civil" war. Or of Armenians out of their lands annexed by Turkey.

Coming out of a vessel (vas=vessel). Could be a tubular vessel such as for blood or lymph, but also a sac-like vessel such as for urine or bile. Malarial parasites coming out of an RBC don't quite cut the mustard.
A reminder for the upcoming podcast:
Ask parasitologist from Mayo clinic about lice & anemia.

My personal guess is that it would not be due to depletion by volume, but perhaps the adaptation of the body of some substance injected by the lice to act as a signal that causes the body to make the blood less nutritious.

And in case Dr. Dickson wants to know what she looks like:

David writes:

Dear Vince,
Long long flight, yes.
What is a chief, but invisible, physiodynamic consequence of even short flights?
Deep vein thrombosis in lower extremities. Cuts loose as ambulating off plane. Throws embolis to lungs, even heart, brain. Pulmonary embolism is a big deal.
Prophylaxis? Wiggle your feet, ankles, calves regularly. Venous return is passive, and hydraulically driven by muscle massage of lower veins in the course of everyday activity.
Lack of activity lets blood accumulate above vein valves. Leg bent at knee, and dependent, further kinks veins. Unmoving blood begins clotting, especially in guys of a certain age. If not troubled in flight, they then walk off plane and collapse.
To prevent, extend legs, and isometrically flex and extend them even when bent. Get up and about in flight at any excuse, and for none.
Alcohol may repress clotting some. At minimally higher risk of uncontrolled bleeding, a bit of aspirin probably wouldn't hurt. Bloody Marys are nutritious.
Travel well. Wish I were there.

Tristen writes:

Dear Vincent and Dixon,
I'm not sure if you got my email a few weeks ago since I sent it from my personal email and not through the website so I'm sending it again just in case.

I have to tell you that I'm a huge fan of TWiP and I love listening to you guys! In November 2013 I did my first medical mission trip to Nzara, South Sudan. Vincent you probably already know an interesting virology fact about Nzara- it's one of the first places Ebola virus was discovered in 1976. After the short trip I enjoyed the work so much that now I am trying to gain funding so I can leave life here and continue the work in Nzara for a couple years. I appreciate how your podcasts are both educational and entertaining at the same time. My favorite one so far is when you had Peter Hotez on talking about neglected tropical diseases.

You guys should really do an episode about chronic malaria infection in children living in sub Saharan Africa and the connection between Epstein Barr virus and the high rate of pediatric burkitts lymphoma diagnosis. People get tired of hearing about malaria, but this would be a great podcast because it combines parasitology and virology. I find it quite interesting and happen to learn about this connection when I had plasmodium malariae after returning from my trip (despite taking malarone). Thank you both for your good work and for giving me such valuable information which I can take back with me to South Sudan!

Malaria-EBV-lymphoma research:



Zephyr writes:

Hello, Doctors Vincent and Dick,

In the episode TWiP 73 (Entamoeba histolytica) I heard the following misconception:

Dick Despommier: (44:33) "Name a mammal that has nucleated red [blood] cells. Camels." (44:35)

In spite of their rather peculiar elliptical shape and other abnormal features (see below), camelid red blood cells are by no means nucleated:

"The elliptical, anucleate erythrocytes of camels have been examined for the presence of marginal bands and their constituent microtubules. Lysis of erythrocytes under microtubule-stabilizing conditions readily revealed marginal bands in at least 3 % of the cells, as observed by phase-contrast and darkfield light microscopy. Microtubules plus a marginal band-encompassing network of material are visible in lysed cell whole mounts with transmission electron microscopy. Marginal band microtubules are also evident in electron micrographs of thin-sectioned camel erythrocytes identifiable as reticuloyctes on the basis of submaximal electron density (reduced haemoglobin iron content) and presence of polysomes. The results suggest that marginal bands may be involved in morphogenesis of camel erythrocytes but are not required for maintenance of their ellipticity after cells are fully differentiated."

“Among the mammals, members of the family Camelidae (camels, vicunas, guanacos, llamas, alpacas) are unique in that their erythrocytes, though anucleate, are elliptical (Andrew, 1965). The question thus arises as to whether MBs play a role in cell shape generation and/or maintenance in these species.”

— Cohen WD and Terwilliger NB. "Marginal bands in camel erythrocytes." J Cell Sci (1979) vol. 36 pp. 97-107
Open access: http://jcs.biologists.org/content/36/1/97.long

More pics of camelid red blood cells, this time from one of the camel’s close relatives, llamas:

• Azwai SM et al. "Morphological characteristics of blood cells in clinically normal adult llamas (Lama glama)." Veterinarski arhiv (2007) vol. 77 (1) pp. 69-79
Open access: http://hrcak.srce.hr/file/39723

It seems to be a rather widespread confusion in educational circles, I also succumbed to this false notion during my undergraduate years. Then one day I decided to look up the possible advantages that could offer the presence of nucleated cells in camels. My wild guess was that perhaps those red blood cells could work in tandem with their also rather peculiar subset of homodimeric immunoglobulins G to keep at bay particularly harmful parasites that might have infested those animals at some point. It turned out that it had nothing to do, and the characteristic elliptical shape of their red blood cells are thought to be an adaptation to extreme dehydration and rapid rehydration, and possibly to increase the efficiency for carrying oxygen at high altitude:

In camels (Cohen and Terwilliger):

“The occurrence of MBs in camel erythrocytes is possibly correlated with ontogeny of distinctive physiological properties. Camels are adapted to survive extreme dehydration and rapid rehydration. Their erythrocytes can withstand considerable osmotic stress, responding in a manner more similar to the elliptical, nucleated erythrocytes of non-mammalian vertebrates than to the biconcave diskoidal cells typical of other mammals (Ponder, 1942; Trotter, 1956). Camel erythrocytes are highly resistant to hypotonic haemolysis (Perk, 1963; Yagil, Sod-Moriah & Meyerstein, 1974), exhibit a low rate of water transport (Naccache & Sha'afi, 1974), and are also relatively stable under hypertonic conditions, in which crenation was not observed (Yagil et al. 1974). In addition, very young camels (6 months or less) apparently possess 2 populations of erythrocytes with respect to osmotic resistance: one population with adult-type response, the other with still greater haemolytic resistance (Pe
rk, 1966). Direct studies of the possible correlation between occurrence of MBs and osmotic resistance in camel erythrocytes would therefore appear to have potential value for understanding MB and erythrocyte function.”

In llamas (Azwai et al.):

“Llamoid erythrocytes were small (7.32 ± 0.95 × 3.9 ± 0.52 μm), elliptical, flat and their counts obtained in the present study (10.3 to 15.0 ×106/ μL) were higher than those in other domestic animals (FELDMAN et al., 2000). The flat shape and the presence of the few folded erythrocytes were attributed to the low thickness to diameter ratio of llama red blood cells (VAN HOUTEN et al., 1992). The small volume resulted in a high concentration of erythrocytes for any given PCV. The high MCHC of llama (38.6 to 48.0 g/dL) in comparison with those in other species might be due to the flat nature of the erythrocytes, which allowed more space for haemoglobin molecules to increase their efficiency for carrying oxygen at high altitude (HAWKEY, 1975). It was evident that llama bone marrow, unlike other ruminants except dromedary camels (MOORE, 2000), was normally releasing immature erythrocytes, including polychromatic rubricytes, metarubricytes (0.8%) and reticulocytes (0.4%) i
nto circulation.”

“In general, the unique elliptical, flat camelid erythrocytes facilitate their movement in capillaries at times of dehydration in arid areas, (SMITH et al., 1979; SMITH et al., 1980) minimizing the likelihood of sludging.”



Curtis writes:

Maybe you've already done a segment on Toxocara and it's hidden under a clever title, but if you haven't done one so far, would you consider doing a podcast?

I just discovered TWIP and what a treasure trove it is! Thanks for all your efforts.



John writes:

Dickson sometimes mentions how crows eat roadkill. They eat the contents of the animal's intestines, rather than its parasite-infested organs. I witnessed a crow eating a California Ground Squirrel and Dickson's explanation helped me understand that the crow was not playing with its food, but rather being picky.

I shot a video, which may be too graphic for some listeners:


Technically my crow is a raven, which is a fancy name for a crow with a big beak.



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