When the fever is absent or insignificant, we consider the malaria latent. The syndrome of such a case frequently rouses less a suspicion of malaria than of the disease imitated by the symptoms.

We must confess that this separation of latent fevers is scarcely justified. The possibility of diagnostic error should not be regarded as a principle on which to base a division, and if it were, all forms of pernicious fever should be placed in the category of latent fevers.

Formerly latent fevers comprised those malarial diseases that ran a completely apyretic course, and it was thought that this was a sufficient basis for classification. Apart from the fact that the presence or absence of fever makes a very weak foundation for a classification, the thermometer has shown that the apyrexia was only apparent, and that in almost all these cases there was an elevation of temperature of from 0.5° to 1.0° and over (Jaccoud). With this discovery the principle fell to the ground, yet the group of latent fevers has been preserved, even though it thrives with difficulty.

The broad, almost immeasurable, field of latent fevers described by Alibert, Bonnet, Griesinger, and others contracts every year. It is especially striking how little has been said about latent fevers since Laveran's discovery. This was surely the time to diagnosticate them as true malaria , yet, instead, we find only isolated reports of examinations, not a few of which were negative. The last word is still to be spoken, though it seems to us to day as if the days of latent fevers were passed.

We will here discuss, first, those facts which stand under a modern criticism, and later the assertions which require corroboration. We may state at once that latent fevers belong among the rarities, and that, remarkable to say, we have almost no examples from severe tropical regions.

During his five years' residence in Algiers Laveran did not observe a single case, although he had the opportunity of treating hundreds of malarial infections of the most different kinds. In contrast to this Bernhardt, in Berlin, observed and treated 20 to 25 cases (trigeminal neuralgia).

Whether latent fevers are more common in cold latitudes than in the severe malarial regions of the south we cannot say. Their relative frequent occurrence in certain localities is striking. In recent years several interesting publications have come from the Caucasus (TriantaphyHides, Zakhariane, Kondriourzkoff), which are especially valuable since the observations are supported by positive blood examinations. Zakhariane had, among 320 soldiers, 148 cases of malaria , of which 27, or 18 per cent., were latent, an enormous figure in comparison to other malarial regions. The so called latent fevers are produced by parasites of the first as well as the second group.

The symptoms, as a rule, are typically intermittent. The most frequent form is the quotidian, the tertian comes next, and the least frequent is the quartan. Continued and remittent symptoms have likewise been observed, though even more rarely. Those affected have usually suffered previously from ordinary malaria or show signs of cachexia. It sometimes happens that normal attacks alternate with latent ones-for instance, after an ordinary tertian the relapse occurs in a latent form.

According to Griesinger, it is particularly irritable people, especially after the fortieth year, who manifest latent attacks. The paroxysms similar to the ordinary malarial paroxysms usually occur in the forenoon hours, and last only a short time-one half to four to six hours.

Sometimes only one definite local symptom is present; again the principal symptom is ushered in by malaise, horripilation, and yawning, and is followed by sweating. The spleen may be enlarged, but this is not usual. The different manifestations, in order of frequency, are:


This is the most common and least contested form of latent fevers.

The neuralgia occurs most frequently in the trigeminal nerve, especially its frontal branch, though occasionally in the infra orbital and mandibular branches. Intercostal and occipital neuralgias, sciatica, hemicrania,* and other complicated neuralgic symptoms,

* For the sake of the historic interest, the personal anamnesis of the celebrated Richardo Morton is here introduced (Pyretologia, Exercitat i, Cap. ix, Historia xxvii): "Anno 1690 a frigore suscepto, Ego ipse, ad quatriduum, insolito faciei calore periodico, praesertim a pastu, affectus sum. Dein per tres vel quatuor dies conas cardialgia, angina pectoris, and enteralgias, have been much less frequently recorded.

The paroxysms of trigeminal neuralgia are often accompanied by a circumscribed flushing and slight swelling of the forehead near the point of exit of the nerve branches. To this are not infrequently added injection of the corresponding eye and increased excretion of tears, associated with photophobia, nausea and vomiting (ophthalmic intermittente). After the termination of the paroxysm sweating may occur on the previously flushed places.

I have seen two cases of such supra orbital latent forms. One was a gentleman of forty five, who suffered, shortly before, from tertian, and who now manifested daily, exactly at midday, a latent paroxysm, accompanied by more or less nausea. The ramus frontalis was not sensitive to pressure. Immediate cure followed the administration of quinin.

The second was a man of fifty who had frequently before suffered from fever paroxysms, looked very cachectic, had a large splenic tumor and edema of the legs. He manifested daily, about 4 o'clock in the afternoon, a right sided frontal headache that continued two to three hours. In the blood only a few crescents were found. During the pain the temperature rose each time to 37.8° to 38.2°. After the treatment with quinin and iron the paroxysms disappeared.

Duboue (de Pau) described a case of sciatica lasting several weeks which yielded to quinin and which he considers as malarial sciatica. In this case the pain was continuous, or at least remittent.