Relationship of UV exposure to prevalence of multiple sclerosis in England.

OBJECTIVE: To assess the potential relationship of ultraviolet B radiation (UVB) and Epstein-Barr virus (EBV) exposure in explaining the period prevalence of multiple sclerosis (MS) in England. METHODS: English national Hospital Episode Statistics covering all admissions to National Health Service hospitals in England in the 7 years from 1998 to 2005 were used to obtain the period prevalences of MS and infectious mononucleosis (IM) in England. The United States National Aeronautics and Space Administration's data on UVB intensity for England from the Nimbus 7 satellite was collected. The relationships among the 3 variables (MS prevalence, IM prevalence, and UVB intensity) were investigated. RESULTS: The regression of MS against UVB intensity for all seasons had an r(2) of 0.61; when including the interaction of IM with seasonal UVB, the r(2) rose to 0.72. CONCLUSIONS: UVB exposure and IM together can explain a substantial proportion of the variance of MS. The effect of UVB on generating vitamin D seems the most likely candidate for explaining its relationship with MS. There is a pressing need to investigate the role of vitamin D and EBV and how they might interact to influence MS risk to identify potential prevention strategies.

The evolution of human skin coloration.

Skin color is one of the most conspicuous ways in which humans vary and has been widely used to define human races. Here we present new evidence indicating that variations in skin color are adaptive, and are related to the regulation of ultraviolet (UV) radiation penetration in the integument and its direct and indirect effects on fitness. Using remotely sensed data on UV radiation levels, hypotheses concerning the distribution of the skin colors of indigenous peoples relative to UV levels were tested quantitatively in this study for the first time. The major results of this study are: (1) skin reflectance is strongly correlated with absolute latitude and UV radiation levels. The highest correlation between skin reflectance and UV levels was observed at 545 nm, near the absorption maximum for oxyhemoglobin, suggesting that the main role of melanin pigmentation in humans is regulation of the effects of UV radiation on the contents of cutaneous blood vessels located in the dermis. (2) Predicted skin reflectances deviated little from observed values. (3) In all populations for which skin reflectance data were available for males and females, females were found to be lighter skinned than males. (4) The clinal gradation of skin coloration observed among indigenous peoples is correlated with UV radiation levels and represents a compromise solution to the conflicting physiological requirements of photoprotection and vitamin D synthesis. The earliest members of the hominid lineage probably had a mostly unpigmented or lightly pigmented integument covered with dark black hair, similar to that of the modern chimpanzee. The evolution of a naked, darkly pigmented integument occurred early in the evolution of the genus Homo. A dark epidermis protected sweat glands from UV-induced injury, thus insuring the integrity of somatic thermoregulation. Of greater significance to individual reproductive success was that highly melanized skin protected against UV-induced photolysis of folate (Branda & Eaton, 1978, Science201, 625-626; Jablonski, 1992, Proc. Australas. Soc. Hum. Biol.5, 455-462, 1999, Med. Hypotheses52, 581-582), a metabolite essential for normal development of the embryonic neural tube (Bower & Stanley, 1989, The Medical Journal of Australia150, 613-619; Medical Research Council Vitamin Research Group, 1991, The Lancet338, 31-37) and spermatogenesis (Cosentino et al., 1990, Proc. Natn. Acad. Sci. U.S.A.87, 1431-1435; Mathur et al., 1977, Fertility Sterility28, 1356-1360).As hominids migrated outside of the tropics, varying degrees of depigmentation evolved in order to permit UVB-induced synthesis of previtamin D(3). The lighter color of female skin may be required to permit synthesis of the relatively higher amounts of vitamin D(3)necessary during pregnancy and lactation. Skin coloration in humans is adaptive and labile. Skin pigmentation levels have changed more than once in human evolution. Because of this, skin coloration is of no value in determining phylogenetic relationships among modern human groups.

Life cycle of Leishmania major (Kinetoplastida: Trypanosomatidae) in the neotropical sand fly Lutzomyia longipalpis (Diptera: Psychodidae).

The development of Leishmania major Yakimoff & Schokhor in the New World sand fly Lutzomyia longipalpis (Lutz & Neiva) was examined by light and electron microscopy. In this unnatural host, parasites differentiated into 10 typical morphological forms, multiplied at three sites, migrated anteriorly and established in the foregut, and attached to gut surfaces. In the blood meal, amastigotes divided and transformed into two successive dividing, stumpy promastigote stages. Elongate nectomonad promastigotes developed from stumpy forms and subsequently rounded up in some flies into paramastigotes and opisthomastigotes. Differentiation into round opisthomastigotes and the apparent fusion of paramastigotes in the blood meal were novel observations in this study. Three nectomonad promastigotes--elongate, short, and metacyclic--were free-swimming in the midgut lumen. Elongate nectomonad promastigotes were highly oriented in the midgut, with their flagella embedded between the epithelial microvilli. Short haptomonad promastigotes were the predominant form attached to the intima of the stomodeal valve, whereas pear-shaped haptomonad promastigotes and paramastigotes colonized surfaces of the esophagus and pharynx. Peripylarian attachment of promastigotes and paramastigotes in the pylorus, ileum, and colon was noted in 21% of flies, suggesting that suprapylarian leishmanias have not lost the ability to colonize the hindgut. L. longipalpis was a successful biological host for L. major, allowing complete development of the parasite.

Ultrastructural development of Leishmania chagasi in its vector, Lutzomyia longipalpis (Diptera: Psychodidae).

The development of Leishmania chagasi, etiologic agent of American visceral leishmaniasis, was studied by light and electron microscopy in the gut of the sand fly, Lutzomyia longipalpis, a natural vector. New aspects of suprapylarian Leishmania behavior were elucidated. In the sand fly midgut, amastigotes transformed into promastigotes (division promastigote I) during a first division sequence within the bloodmeal. Secondary division of these promastigotes resulted in a second form (division promastigote II), and these subsequently elongated into nectomonad promastigotes. Nectomonads existed in long and short populations which divided in the bloodmeal and throughout the midgut lumen after escape from the peritrophic membrane. Nectomonads adhered to the midgut cells in a highly organized manner, with their flagella embedded deep into microvilli and cytoplasm. Migration of parasites from the posterior midgut into the cardia/stomodeal valve region at 36 hr was associated with breakdown of the peritrophic membrane anteriorly. Posterior breakdown at 48 hr resulted in a peritrophic tube open at both ends containing some parasites within the digesting bloodmeal for up to 6 days postinfection. At the stomodeal valve, a myriad of slender and rounded promastigotes attached to the intima by flagellar hemidesmosomes; these may represent a transformation sequence from slender nectomonads to pear-shaped haptomonads. Pear-shaped forms appear to be precursors of paramastigotes, which also attached to the valve intima. Both rounded haptomonads and paramastigotes were found in the esophagus, dividing in a complex sequence initiated by posterior cleavage of the cytoplasm producing unique heart-shaped forms. Dividing paramastigotes also colonized the pharynx up to the cibarial valve. The ultrastructure of paramastigotes suggested that they may be infective forms, capable of some motility in the foregut. Free-swimming "infective" promastigotes were observed throughout the midgut and foregut, were attached in the pharynx (armature region), and were associated with the labrum-epipharynx of the proboscis in 3.6% of flies (16 days). The fine structure of hemidesmosomes in the foregut showed regional specializations, including the presence of plasmalemmar bridges in the gap space.

Ultrastructural biology of Leishmania (Viannia) panamensis (=Leishmania braziliensis panamensis) in Lutzomyia gomezi (Diptera: Psychodidae): a natural host-parasite association.

The development of Leishmania (Viannia) panamensis in a natural sand fly host, Lutzomyia gomezi, was studied by light and transmission electron microscopy. New aspects of peripylarian parasite behavior and morphology in the sand fly gut, early bloodmeal stages, and ultrastructural development in the anterior gut were documented. Eight distinct morphological forms were observed in the life cycle of the parasite within the insect. In the bloodmeal, amastigotes (1) transformed into stumpy promastigotes (2) which rapidly multiplied, resulting in spatulate-shaped nectomonad promastigotes (3) and elongate nectomonad promastigotes (4). These latter forms migrated primarily into the hindgut, where both were observed attached (=haptomonad phase) to the cuticular intima by hemidesmosomes within extremely shortened flagella. Spatulate haptomonad promastigotes predominated, colonizing the entire length of the hindgut, with the greatest density at 2 disjunct sites: the pylorus/ileum and the anterior rectum/rectal sac. Paramastigotes and dividing flagellates were rare. Some parasites migrated directly to the cardia/stomodeal valve region without a hindgut phase; however, major movement anteriorly was from the hindgut beginning at 6 days postinfection. In the cardia lumen, dividing short Type A promastigotes (5) predominated, intermixed with short Type B promastigotes with longer flagella (6). Paramastigotes (7) were free-swimming in the lumen as well as attached to the stomodeal valve. The primary colonizers of the valve were pear-shaped haptomonad promastigotes (8), with flagella of variable lengths and multi-segmented hemidesmosomal attachment points to the intima. Promastigotes and paramastigotes colonized the esophagus-pharynx region and attached to the foregut lining by flagellar hemidesmosomes. Both forms may represent infective stages of L. (V.) panamensis; however, no parasites were detected in the cibarium or proboscis. L. (V.) panamensis appeared well-adapted to the gut of Lu. gomezi, multiplying extensively at 2 sites, changing morphological form, and adhering to host surfaces by variously modified flagellar hemidesmosomes.