Recent Advances in Our Knowledge of the Myxozoa

In the last few years two factors have helped to significantly advance our understanding of the Myxozoa. First, the phenomenal increase in fin fish aquaculture in the 1990s has lead to the increased importance of these parasites; in turn this has lead to intensified research efforts, which have increased knowledge of the development, diagnosis. and pathogenesis of myxozoans. The hallmark discovery in the 1980s that the life cycle of Myxobolus cerebralis requires development of an actinosporean stage in the oligochaete. Tubifex tubifex, led to the elucidation of the life cycles of several other myxozoans. Also, the life cycle and taxonomy of the enigmatic PKX myxozoan has been resolved: it is the alternate stage of the unusual myxozoan, Tetracapsula bryosalmonae, from bryozoans. The 18S rDNA gene of many species has been sequenced, and here we add 22 new sequences to the data set. Phylogenetic analyses using all these sequences indicate that: 1) the Myxozoa are closely related to Cnidaria (also supported by morphological data); 2) marine taxa at the genus level branch separately from genera that usually infect freshwater fishes; 3) taxa cluster more by development and tissue location than by spore morphology; 4) the tetracapsulids branched off early in myxozoan evolution, perhaps reflected by their having bryozoan, rather than annelid hosts; 5) the morphology of actinosporeans offers little information for determining their myxosporean counterparts (assuming that they exist); and 6) the marine actinosporeans from Australia appear to form a clade within the platysporinid myxosporeans. Ribosomal DNA sequences have also enabled development of diagnostic tests for myxozoans. PCR and in situ hybridisation tests based on rDNA sequences have been developed for Myxobolus cerebralis, Ceratomyxa shasta, Kudoa spp., and Tetracapsula bryosalmonae (PKX). Lectin-based and antibody tests have also been developed for certain myxozoans, such as PKX and C. shasta. We also review important diseases caused by myxozoans, which are emerging or re-emerging. Epizootics of whirling disease in wild rainbow trout (Oncorhynchus mykiss) have recently been reported throughout the Rocky Mountain states of the USA. With a dramatic increase in aquaculture of fishes using marine netpens, several marine myxozoans have been recognized or elevated in status as pathological agents. Kudoa thyrsites infections have caused severe post-harvest myoliquefaction in pen-reared Atlantic salmon (Salmo salar), and Ceratomyxa spp., Sphaerospora spp., and Myxidium leei cause disease in pen-reared sea bass (Dicentrarchus labrax) and sea bream species (family Sparidae) in Mediterranean countries.     

Recent Advances in Medical Knowledge of Causes of Mental Retardation

A steady reduction of mortality owing to advances in medicine has altered the patterns of disease, increasing the proportionate importance of certain types of disease in the very young and the very old.Neonatal and infant mortality rates in mongolism remain very high. The mortality has nevertheless fallen considerably and this may well be so for other diseases causing mental retardation.Despite dramatic advances in the fields of biochemistry and cytogenetics, revealing many new causes of mental retardation, a large proportion of mentally retarded patients are still undiagnosable in respect of etiology.Other principles of causation, not so often discussed in the medical literature, deserve consideration, e.g. isoimmunization due to other antigens than those of the blood groups and diseases due to deficiency of some trace element. Peculiarities of distribution, geographical, seasonal, occupational or social, merit examination, and recent research along these lines has led to significant results. Whole classes of causes may not have occurred to us, and it may prove fruitful in this respect to turn our minds toward less fashionable paths of thought.     

Some Recent Advances in Our Understanding of Parasitic Protozoa*†

SYNOPSIS. Striking progress in our understanding of parasitic protozoa has been achieved thru the employment of advanced electron-microscopic, biochemical, immunologic, and cultivation methods. Some recent information gathered by means of these methods on trichomonad and trypanosomatid flagellates as well as on eimeriidian and plasmodiid haemosporiidian Sporozoa is discussed. It is emphasized that the parasitic protozoa when studied by the presently available sophisticated methods in the context of being parasites, not merely cells maintained on refined media, can aid us greatly in illuminating the highly complex functional aspects of host-parasite interactions.     

Recent Advances in Neuroblastoma

Neuroblastoma is one of the commoner tumors of infancy and childhood. There is great variation in the histological picture and even within one tumor. One unique feature is the apparently high rate of spontaneous regression, particularly during the first year of life. There is also a tendency for neuroblastoma to mature to the more benign ganglioneuroma and recent in vitro studies suggest that a serum factor may influence this process. Approximately 90 percent of patients with neuroblastoma excrete abnormally high quantities of various catecholamines, thus providing a useful diagnostic tool and a means for evaluating the effect of therapy.Treatment requires a multidisciplinary team approach involving a surgeon, radiotherapist and chemotherapist. Prognosis is influenced by a number of host factors and the most important of these seem to be the patient''s age at diagnosis and the extent of the disease, although some children with widespread disease appear to have a particularly good prognosis. It is difficult to evaluate the influence of chemotherapy on survival in patients with neuroblastoma but it has not been of great significance. The unique biologic characteristics of this tumor require further study in the hope of providing more effective therapy.     

Recent Advances in Hypertension

The possible relationship between the renal mechanism of volume control and blood pressure regulation is discussed. Expansion of the extracellular fluid (ECF) and plasma volumes was demonstrated following renal artery constriction in the rat; after about one month ECF volume returned to normal although hypertension persisted. Measurements of cardiac output in the unanesthetized rat by an implanted electromagnetic flowmeter showed an initial rise in cardiac output after renal artery constriction, returning to normal in 10 to 15 days. A homeostatic hypothesis for the production of renal hypertension is put forward in which changes in ECF volume, capacity vessel tone and myocardial contractility participate in the development of hypertension by elevating cardiac output. Autoregulation of peripheral flow then occurs and the consequent restoration of blood pressure at a renal pressure receptor results in return to normal of cardiac output by negative feedback. Thus in chronic hypertension the high peripheral resistance is maintained by autoregulation.