Chapter XLV: Blood Examinations in the Diagnosis of Tropical Diseases (3)

_Trypanosomiasis._—While the blood, when examined in ordinary smears or with thick-film methods, does not give as good results as by examining the gland juice for trypanosomes, yet, by taking 5 or 10 cc. of blood in citrated salt solution with 2 or 3 centrifugalizations, we may obtain greater success in finding the parasites in this way than when using gland juice.

In wet preparations we may note the clumping of the red cells.
This is the phenomenon of auto-agglutination thought by some to be
rather characteristic of trypanosomiasis.

We may carry out the leucocyte attachment test using the inactivated serum of the suspected patient.

As the disease progresses we get a secondary anaemia. The leucocyte
count is usually normal but the differential count shows an
increase in the large mononuclears. Bacterial infections often
supervene when a leucocytosis will be noted.

_Kala-azar._—Quite recently there has been success in the diagnosis of kala-azar by culturing the blood of the suspect on N. N. N. medium. The key to success when culturing from the blood is to wait for two or three weeks before giving up the examination of the cultures. It will be remembered that almost invariably leishman bodies are present in the blood only in extremely small numbers so that there is not time by the end of a few days for sufficient development to have taken place. In probably 80% of cases the parasite of kala-azar may be found in stained smears from the peripheral blood but only after prolonged and patient search. They may be found phagocytized by large mononuclears or polymorphonuclears. Of course splenic puncture examinations show far greater abundance of parasites than blood smears but it is not without danger.

The marked anaemia of kala-azar does not appear until the earlier
symptoms of fever and splenic enlargement have gone on for some
time. Very characteristic and important in diagnosis, however, is
the marked leucopenia of kala-azar, approximating 2000 leucocytes
on the average. Again the white cells are only about in the
proportion of 1 to 1000 red cells. There is an increase in the
percentage of large mononuclears. Some authorities have reported an
acidosis of the blood serum. Coagulation rate is delayed.

In kala-azar the coagulability of the serum is altered as shown by
the formol-gel test. In this test, a drop of clear serum from the
patient is placed on a slide which is then inverted over a watch
glass containing a few drops of liquor formaldehyde. In cases of
kala-azar the serum will solidify, appearing as an opaque, stiff
jelly which adheres to the slide; while other sera will remain
fluid, running off the slide when it is tilted. The reaction
appears not to be specific since it has been reported for syphilis
and other diseases.

_Relapsing Fever._—The spirochaetes are not so numerous in the blood of the peripheral circulation in tropical relapsing fevers as in those of Europe.

The spirochaetes can best be seen in stained smears but the
agitation of the red cells in a wet preparation by the motile
spiral organisms is of assistance in their recognition. Dark-field
illumination, India ink smears and Fontana’s silver method are used
as well as Giemsa staining.

During the afebrile period the parasites disappear from the peripheral circulation.

If the disease is first seen during the afebrile stage we may try
Lowenthal’s reaction, which consists in taking a drop of the blood
of the suspected patient, mixing it on a vaseline ringed slide with
the blood of a patient showing spirochaetes, then covering with a
cover-glass and incubating for thirty minutes at 37°C. A positive
reaction shows clumping and loss of motility of the spirochaetes.

Reports vary as to the white count but on the whole there would
seem to be more evidence in favor of a moderate leucocytosis
although some observers have noted a fall from the normal. The
usual statements give a leucocytosis of from 12 to 15 thousand with
a polymorphonuclear increase to between 75 and 80%. The statement
is usually made that the normal percentage of large mononuclears
helps in the differentiation of malaria. Kieseritzky has reported
leucopenia and slight increase in lymphocytes.

The leucocyte count tends to be higher about the time of crisis.

_Weil’s Disease._—This spirochaete infection is due to _Leptospira icterohaemorrhagiae_. The spirochaete has been found in the blood and has possibly been cultured anaerobically from the blood. The practical method is by inoculating guinea pigs with blood or urine sediment. Spirochaetes are found in the liver smears of the sick guinea pigs. In the first week of Weil’s disease we have a leucocytosis—later on a leucopenia.

_Filariasis._—The sheathed embryos of _Filaria bancrofti_ are found in the peripheral circulation at night only, hence _F. nocturna_, while those of _F. loa_ are only to be found in the daytime, hence _F. diurna_. In the islands of the South Pacific the filarial infection is considered as of _F. bancrofti_ but the embryos are present in the peripheral circulation both by day and by night.

Instead of being uncommon it seems rather to be the rule to fail
to find embryos in the blood preparations in cases showing marked
evidences of filarial disease, as in elephantiasis, calabar
swellings, etc. The positive blood findings are most frequent in
those who do not as yet show symptoms. There has not yet been
sufficient obstruction in the lymphatics to keep the embryos from
reaching the blood stream.

In some countries where a large percentage of the population may show embryos in the peripheral circulation, manifestations of the disease are very rare.

We may examine the blood either with fresh preparations, when the
movements of the embryos assist in their detection, or by staining
dried smears. Haematoxylin staining is better than the Romanowsky
one as the break in cells and other points are better brought out.

An eosinophilia is usually considered as constantly present but
this is not invariable. The leucocyte count is about normal.

_Dengue and Phlebotomus Fever._—In these diseases a leucopenia, which begins to show itself by the second day, is very characteristic.

The average leucocyte count is about 3500 and along with this we
have a reduction in the percentage of polymorphonuclears to about
50%. Towards the end of the terminal fever we have an increase in
the percentage of large mononuclears.

_Bacillary Dysentery._—The agglutination tests are of little value in diagnosing the presence of or type of an infection with dysentery bacilli, as the agglutinating power does not appear until during convalescence.

It is now customary to use a polyvalent antidysenteric serum
in treatment so that it is not very essential to ascertain the
strain involved in an infection. As a practical matter we make our
diagnosis of the presence as well as type of dysentery bacillus
involved in an infection by isolating the organism from the
dysenteric stool.

During the fever we may have a moderate polymorphonuclear
leucocytosis.

_Enteric Group of Fevers._—In fevers of atypical course in the tropics one must always remember that _typhoid_ and the _paratyphoid fevers_ are anything but uncommon and blood cultures should always be made when such suspicion arises. In some tropical regions paratyphoid A infections seem most common although the usual experience is to encounter the paratyphoid B infection more frequently. In temperate climates the noting of a moderate leucopenia with an absence of eosinophiles is important in the diagnosis of typhoid, but in the tropics there are so many intestinal parasites and skin infections productive of eosinophilia that we cannot attach any importance to such a finding.

_Typhus Fever._—Plotz attaches importance to the culturing of _B. typhi exanthematici_ from the blood of typhus cases, but the relationship is now regarded as not causal. _Rickettsia_ bodies, which can be demonstrated in the louse or in capillaries at autopsy, are now considered to be the exciting organism.

A mononuclear leucocytosis has at times been reported.

_Spotted Fever of the Rocky Mountains._—Injection of the blood of the patient into guinea pigs produces the disease in the animal. Frick has reported the finding of chromatin-staining bodies in the red cells of such pigs and Wolbach has found chromatin-staining bacteria in the endothelial cells of such animals. These bodies are now classed as _Rickettsia_.

These findings cannot as yet be considered of diagnostic value.

_Various Helminthological Infections._—In the earlier stages of ancylostomiasis and schistosomiasis we have a rather notable increase in the percentage of eosinophiles but with the advanced stages of these infections, with severe anaemia, the eosinophiles may even be absent.

One should always keep in mind the very characteristic and marked
eosinophilia of _trichinosis_ when such a blood finding is
encountered. There is often a leucocytosis of 15,000 to 20,000 in
this disease.

In the _urticarial fever_ stage of _Japanese schistosomiasis_ the marked eosinophilia is of great assistance in diagnosis. One trouble about attaching importance to eosinophilia in the tropics is the confusion which is difficult to eliminate and which arises from infections with the more common but less important group of intestinal parasites such as _Ascaris_, _Trichuris_, etc.

The eosinophilia-producing characteristics of many skin diseases
must also be kept in mind.