Toxoplasma gondii: from animals to humans

A methodical gross examination should be undertaken in all births and the results incorporated in the patient’s record.

The Pathology of the Human Placenta

In this paper the history of Toxoplasma gondii and toxoplasmosis is reviewed. This protozoan parasite was first discovered in 1908 and named a year later. Its medical importance remained unknown until 1939 when T. gondii was identified in tissues of a congenitally infected infant, and veterinary importance became known when it was found to cause abortion storms in sheep in 1957. The discovery of a T. gondii specific antibody test, Sabin-Feldman dye test in 1948 led to the recognition that T. gondii is a common parasite of warm-blooded hosts with a worldwide distribution. Its life cycle was not discovered until 1970 when it was found that felids are its definitive host and an environmentally resistant stage (oocyst) is excreted in feces of infected cats. The recent discovery of its common infection in certain marine wildlife (sea otters) indicates contamination of our seas with T. gondii oocysts washed from land. Hygeine remains the best preventive measure because currently there is no vaccine to prevent toxoplasmosis in humans.

The history of Toxoplasma gondii--the first 100 years.

Electrical resistance of metals

History of the discovery of the life cycle of Toxoplasma gondii.

SummaryThe customary method of transmission of toxoplasmsis to man and to animals remains unknown. This report shows that infections are transmitted between swine and rodents when either animal is fed infected tissue from the other, likewise when pigs ingest infected swine offal. The feeding cycles described are reminiscent of those known in trichinosis. Similarities and differences are discussed, and implications for human disease pointed out. Whether there is a risk to the public, and if so, its extent, will require future studies on swine and on pork, under natural as well as experimental conditions.

Toxoplasmosis in swine and rodents; reciprocal oral infection and potential human hazard.

Today, toxoplasmosis is considered to be one of the very common infections of man—an opinion that is contrary to that held 10 years ago. However, most of these infections are well tolerated, and usually it is only the exceptional acute case that receives clinical attention and postmortem verification. Data on prevalence derive, therefore, not from clinical studies but from surveys based on serologic data or skin tests. These surveys, regardless of type, show roughly the same findings: The number of infected individuals 0-5 years of age is low, with the number increasing at 5 years of age. From this age onward the increase is progressive, reaching a peak sometime after individuals reach 40 years of age. It is not widely known perhaps that peak incidences in the United States range from 30 to 70% of the population at ages of from 40 to 60 years, the precise figures varying according

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Toxoplasmosis in man and swine—an investigation of the possible relationship

1. 1) The method described made it possible to cultivate T. gambiense and T. rhodesiense readily from patients. 2. 2) Cultures were established with equal ease from blood or from spinal fluid. 3. 3) The method proved to be sensitive, detecting blood and spinal fluid infections ignored by current diagnostic procedures. Thus, approximately 20 per cent. of “negative suspects” from an epidemic area were shown to be infected. Conventional methods were particularly poor for cerebrospinal fluid examination, detecting only 10 per cent. of those obtained by culture. 4. 4) The method is reliable. We have no evidence that trypanosomes failed to grow in pure culture. However, under African field and hospital conditions, many cultures were inconclusive because of contamination. 5. 5) An independent means for estimating the accuracy of conventional diagnostic methods is now provided. It is clear that these conventional methods are often in error, and that the error is always in one direction: that of underestimation. Accordingly, certain earlier investigations require re-evaluation, since failure to detect trypanosomes signifies not that the micro-organisms were absent, as was supposed, but only that the limit of sensitivity of the method had been reached. 6. 6) The culture method should prove to be a useful tool for the investigation of a number of problems which have hitherto resisted analysis.

Cultivation of the African sleeping sickness trypanosomes from the blood and cerebrospinal fluid of patients and suspects.

This paper deals with the African sleeping sickness trypanosomes, their cultivation and certain properties of the culture forms. To those who are not working on this problem, the status of the cultivation of Trypanosoma gambiense and Trypanosoma rhodesiense may not be clear. Standard references state that cultivation can be achieved, but only irregularly -or that such a worker in such a year claimed to have grown one of these species. Any reference to current field work in Africa shows that the method is not used for diagnosis.8 Thus, the net impression given is that successful cultivation is rather a rarity, perhaps achieved only with anomalous strains. Actually, with the isolation medium which I will describe later, successful cultures of fresh strains can be made from very nearly 100 per cent of all infected laboratory animals and in the neighborhood of 70-80 per cent of all attempts at isolation; that is, repeated cultures may be necessary in perhaps 20-30 per cent of all infected animals. Furthermore, since these cultures can be maintained indefinitely by serial transfer, there is no difficulty in carrying these organisms in the laboratory for experimental purposes. There are several media available, each with respective advantages and drawbacks. In general, isolation and maintenance media should be distinguished. Isolation from the animal will fail with certain media which are, however, perfectly satisfactory for subcultures, once growth has been established in vitro. The medium with which I have the greatest experience is a blood nutrient agar slant with only three peculiarities: it contains human blood; the blood contains sodium citrate as an anticoagulant (ACD mixtures are unsatisfactory) ; the human blood is inactivated; and the red cells washed before incorporation in the medium?’ This medium has given me throughout four or five years of study a greater number of isolations than any other and, consequently, I shall refer to it as isolation medium. For example, we are now working with a strain of Trypanosoma gambiense which could properly be called neurotropic. I t is of low virulence and mice die about 12 months after inoculation, showing paralysis of the posterior train. Yet trypanosomes are extremely difficult to demonstrate by any of the usual methods. It may require 15, 20, or 25 blood examinations before the animal is proved to be infected. Inoculation of fresh animals is no help, for the same type of infection is reproduced. Yet the cultures readily detect infection and this is the only method which can be easily and successfully applied to the live animals. Isolation medium may be indispensable for certain experimental work.

David Weinman

Papers

Toxoplasmosis in swine and rodents; reciprocal oral infection and potential human hazard.

Toxoplasmosis in man and swine—an investigation of the possible relationship

Cultivation of the African sleeping sickness trypanosomes from the blood and cerebrospinal fluid of patients and suspects.

African sleeping sickness trypanosomes: cultivation and properties of the culture forms

Trypanosoma cyclops n. sp.: A pigmented trypanosome from the Malaysian primates Macaca nemestrina and M. Ira☆