CHAPTER X

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA [_Continued_]

ARTHROPODS AND SPIROCHAETOSES OF MAN AND ANIMALS

The term spirochaetoses is applied to diseases of man or animals which are due to protistan parasites belonging to the group of slender, spiral organisms known as spirochaetes.

There has been much discussion concerning the relationship Of the spirochaetes. Formerly, they were regarded as bacteria closely related to the forms grouped in the genus _Spirillum_. The results of the detailed study which the spirochaetes have received in recent years, have led most of the workers to consider them as belonging to the protozoa. The merits of the discussion we are not concerned with here, but rather with the fact that a number of diseases caused by spirochaetes are arthropod-borne. The better known of these we shall discuss.

AFRICAN RELAPSING FEVER OF MAN--It has long been known to the natives of Africa and to travelers in that country, that the bite of a certain tick, _Ornithodoros moubata_, may be followed by severe or even fatal fever of the relapsing type. Until recent years, it was supposed that the effect was due to some special virulence of the tick, just as nagana of cattle was attributed to the direct effect of the bite of the tsetse-fly. The disease is commonly known as "tick-fever" or by the various native names of the tick.

In 1904, Ross and Milne, in Uganda, and Dutton and Todd on the Congo, discovered that the cause of the disease is a spirochaete which is transmitted by the tick. This organism has been designated by Novy and Knapp as _Spirochaeta duttoni_.

_Ornithodoros moubata_ (fig. 142), the carrier of African relapsing fever, or "tick-fever," is widely distributed in tropical Africa, and occurs in great numbers in the huts of natives, in the dust, cracks and crevices of the dirt floors, or the walls. It feeds voraciously on man as well as upon birds and mammals. Like others of the _Argasidae_, it resembles the bed-bug in its habit of feeding primarily at night. Dutton and Todd observed that the larval stage is undergone in the egg and that the first free stage is that of the octopod nymph.

[Illustration: 142. Ornithodoros moubata. (_a_) Anterior part of venter; (_b_) second stage nymph; (_c_) capitulum; (_d_) dorsal and (_e_) ventral aspect of female; (_f_) ventral aspect of nymph; (_g_) capitulum of nymph. After Nuttall and Warburton.]

The evidence that the fever is transmitted by this tick is conclusive. Koch found that from five per cent to fifteen per cent, and in some places, fifty per cent of the ticks captured, harbored the spirochaete. The disease is readily transmitted to monkeys, rats, mice and other animals and the earlier experiments along these lines have been confirmed by many workers.

Not only are the ticks which have fed on infected individuals capable of conveying the disease to healthy animals but they transmit the causative organism to their progeny. Thus Mollers (1907), working in Berlin, repeatedly infected monkeys through the bites of nymphs which had been bred in the laboratory from infected ticks. Still more astonishing was his discovery that ticks of the third generation were infective. In other words, if the progeny of infected ticks were fed throughout life on healthy animals, and on maturity deposited eggs, the nymphs which hatched from these eggs would still be capable of carrying the infection.

The developmental cycle of the spirochaete within the tick has not been fully worked out, though the general conclusions of Leishman (1910) have been supported by the recent works of Balfour (1911 and 1912), and Hindle (1912), on the life cycle of spirochaetes affecting fowls.

_Spirochaeta duttoni_ ingested by _Ornithodoros moubata_ apparently disappear within a few days, but Leishman believed that in reality they break up into minute granules which are to be found in the alimentary canal, the salivary glands and the Malpighian tubes of the tick. These granules, or "coccoid bodies," as Hindle calls them, are supposed to be the form in which the spirochaetes infect the new host. We shall see later that Marchoux and Couvy (1913) dissent wholly from this interpretation.

According to Leishman, and Hindle, the coccoid bodies are not injected into the vertebrate host with the saliva of the tick, as are the sporozoites of malaria with that of the mosquito. Instead, they pass out with the excrement and secondarily gain access to the wound inflicted by the tick.

Nuttall (1912) calls attention to the fact that the geographical distribution of _Ornithodoros moubata_ is far wider than our present records show for the distribution of the relapsing fever in man and that there is every reason to fear the extension of the disease. Huts where the ticks occur should be avoided and it should be remembered that in infected localities there is special danger in sleeping on the ground.

EUROPEAN RELAPSING FEVER--There is widely distributed in Europe a type of relapsing fever which is caused by _Spirochaeta recurrentis_. It has long been supposed that this disease is spread by the bed-bug and there is some experimental evidence to show that it may be conveyed by these insects.

In 1897, Tictin found that he could infect monkeys by inoculating the contents of bed-bugs which had fed upon a patient within forty-eight hours. Nuttall, in 1907, in one experiment succeeded in transmitting _Spirochaeta recurrentis_ from mouse to mouse by bites of bed-bugs. The bugs, thirty-five in number, were transferred at short intervals from one mouse to another, not being allowed to take a full meal on the first, or infected mouse.

On the other hand, there is much clinical evidence to show that the European relapsing fever like various other types of the disease is transmitted from man to man by head and body lice (_Pediculus humanus_ and _Pediculus corporis_).

Interesting supplementary evidence is that of Bayon's observations (1912), in Moscow. "Having visited the big municipal night hospitals at Moscow I soon noticed that they were kept with such scrupulous cleanliness, disinfected so lavishly, the beds of iron, the floor cemented, that it was not possible for bed-bugs to thrive to any extent on the premises. The people sleeping there were allowed, however, to sleep in their own clothes. The introduction of these model homes had not had any effect on the incidence of relapsing fever, for the places were still hot-beds of the fever during winter. On the other hand, though I changed my rooms several times, I found bugs in every successive lodging, and I was told in Moscow, this can hardly be avoided. Yet no foreigner, or Russian of the better class, ever catches relapsing fever. To this may be added the fact that when I asked for clothes-lice and promised to pay a kopec for two, the attendants from the night hostel brought me next morning a small ounce bottle crammed with _Pediculus capitis_ (= _P. humanus_), and _Pediculus vestimentorum_ (= _P. corporis_) collected off the sleepers. If relapsing fever were transmitted by bed-bugs, it would be much more disseminated than it is at present in Moscow."

Direct experimental evidence of the agency of lice in transmitting relapsing fever is especially clear in the case of a type of the disease prevalent in parts of North Africa. We shall consider this evidence later.

OTHER TYPES OF RELAPSING FEVER OF MAN--In addition to the three types of human relapsing fever already referred to, several others have been distinguished and have been attributed to distinct species of spirochaetes. The various spirochaetoses of man are:

African, caused by _S. duttoni_; European, caused by _S. recurrentis_; North African, caused by _S. berbera_; East African, caused by _S. rossi_; East Indian, caused by _S. carteri_; North American, caused by _S. novyi_; South American, caused by _S. duttoni_ (?).

Nuttall (1912) in his valuable resume of the subject, has emphasized that "in view of the morphological similarity of the supposedly different species of spirochaetes and their individual variations in virulence, we may well doubt if any of the 'species' are valid. As I pointed out four years ago, the various specific names given to the spirochaetes causing relapsing fever in man may be used merely for convenience _to distinguish strains or races_ of different origin. They cannot be regarded as valid names, in the sense of scientific nomenclature, for virulence and immunity reactions are not adequate tests of specificity."

NORTH AFRICAN RELAPSING FEVER OF MAN--The type of human relapsing fever to be met with in Algeria, Tunis, and Tripoli, is due to a _Spirochaeta_ to which does not differ morphologically from _Spirochaeta duttoni_, but which has been separated on biological grounds as _Spirochaeta berberi_.

Experimenting with this type of disease in Algeria, Sergent and Foly (1910), twice succeeded in transmitting it from man to monkeys by inoculation of crushed body lice and in two cases obtained infection of human subjects who had received infected lice under their clothing and who slept under coverings harboring many of the lice which had fed upon a patient. Their results were negative with _Argas persicus_, _Cimex lectularius_, _Musca domestica_, _Haematopinus spinulosus_ and _Ceratophyllus fasciatus_. They found body lice associated with every case of relapsing fever which they found in Algeria.

Nicolle, Blaizot, and Conseil (1912) showed that the louse did not transmit the parasite by its bite. Two or three hours after it has fed on a patient, the spirochaetes begin to break up and finally they disappear, so that after a day, repeated examinations fail to reveal them. They persist, nevertheless, in some unknown form, for if the observations are continued they reappear in eight to twelve days. These new forms are virulent, for a monkey was infected by inoculating a single crushed louse which had fed on infected blood fifteen days before.

Natural infection is indirect. Those attacked by the insect scratch, and in this act they excoriate the skin, crush the lice and contaminate their fingers. The least abrasion of the skin serves for the entrance of the spirochaetes. Even the contact of the soiled fingers on the various mucosa, such as the conjunctive of the eye, is sufficient.

As in the case of _Spirochaeta duttoni_, the organism is transmitted hereditarily in the arthropod vector. The progeny of lice which have fed on infected blood may themselves be infective.

SPIROCHAETOSIS OF FOWLS--One of the best known of the spirochaetes transmitted by arthropods is _Spirochaeta gallinarum_, the cause of a very fatal disease of domestic fowls in widely separated regions of the world. According to Nuttall, it occurs in Southeastern Europe, Asia, Africa, South America and Australia.

In 1903, Marchoux and Salimbeni, working in Brazil, made the first detailed study of the disease, and showed that the causative organism is transmitted from fowl to fowl by the tick _Argas persicus_. They found that the ticks remained infective for at least five months. Specimens which had fed upon diseased birds in Brazil were sent to Nuttall and he promptly confirmed the experiments. Since that date many investigators, notably Balfour and Hindle, have contributed to the elucidating of the life-cycle of the parasite. Since it has been worked out more fully than has that of any of the human spirochaetes, we present Hindle's diagram (fig. 143) and quote the brief summary from his preliminary paper (1911_b_).

"Commencing with the ordinary parasite in the blood of the fowl, the spirochaete grows until it reaches a certain length (16-19u) and then divides by transverse division. This process is repeated, and is probably the only method of multiplication of the parasite within the blood. When the spirochaetes disappear from the circulation, some of them break up into the coccoid bodies which, however, do not usually develop in the fowl. When the spirochaetes are ingested by _Argas persicus_, some of them pass through the gut wall into the coelomic fluid. From this medium they bore their way into the cells of the various organs of the tick and there break up into a number of coccoid bodies. These intracellular forms multiply by ordinary fission in the cells of the Malpighian tubules and gonads. Some of the coccoid bodies are formed in the lumen of the gut and Malpighian tubules. The result is that some of the coccoid bodies may be present in the Malpighian secretion and excrement of an infected tick and when mixed with the coxal fluid may gain entry into another fowl by the open wound caused by the tick's bite. They then elongate and redevelop into ordinary spirochaetes in the blood of the fowl, and the cycle may be repeated."

[Illustration: 143. Spirochaeta gallinarum. After Hindle.]

Hindle's account is clear cut and circumstantial, and is quite in line with the work of Balfour, and of Leishman. Radically different is the interpretation of Marchoux and Couvy (1913). These investigators maintain that the granules localized in the Malpighian tubules in the larvae and, in the adult, also in the ovules and the genital ducts of the male and female, are not derived from spirochaetes but that they exist normally in many acariens. They interpret the supposed disassociation of the spirochaete into granules as simply the first phase, not of a process of multiplication, but of a degeneration ending in the death of the parasite. The fragmented chromatin has lost its affinity for stains, remaining always paler than that of the normal spirochaetes. On the other hand, the granules of Leishman stain energetically with all the basic stains.

Further, according to Marchoux and Couvy, infection takes place without the emission of the coxal fluid and indeed, soiling of the host by the coxal fluid diluting the excrement is exceptional. All of the organs of the Argasid are invaded by the parasites, but they pass from the coelom into the acini of the salivary glands and collect in its efferent canal. The saliva serves as the vehicle of infection.

Thus, the question of the life cycle of _Spirochaeta gallinarum_, and of spirochaetes in general, is an open one.

It should be noted that _Argas persicus_, the carrier of _Spirochaeta gallinarum_, is a common pest of poultry in the southwestern United States. Though the disease has not been reported from this country, conditions are such that if accidentally introduced, it might do great damage.

OTHER SPIROCHAETE DISEASES OF ANIMALS--About a score of other blood inhabiting spirochaetes have been reported as occurring in mammals, but little is known concerning their life-histories. One of the most important is _Spirochaeta theileri_ which produces a spirochaetosis of cattle in the Transvaal. Theiler has determined that it is transmitted by an Ixodid tick, _Margaropus decoloratus_.

TYPHUS FEVER AND PEDICULIDAE

Typhus is an acute, and continued fever, formerly epidemically prevalent in camps, hospitals, jails, and similar places where persons were crowded together under insanitary conditions. It is accompanied by a characteristic rash, which gives the disease the common name of "spotted" or "lenticular" fever. The causative organism is unknown.

Typhus fever has not generally been supposed to occur in the United States, but there have been a few outbreaks and sporadic cases recognized. According to Anderson and Goldberger (1912_a_), it has been a subject of speculation among health authorities why, in spite of the arrival of occasional cases in this country and of many persons from endemic foci of the disease, typhus fever apparently does not gain a foothold in the United States. These same workers showed that the so-called Brill's disease, studied especially in New York City, is identical with the typhus fever of Mexico and of Europe.

The conditions under which the disease occurs and under which it spreads most rapidly are such as to suggest that it is carried by some parasitic insect. On epidemiological grounds the insects most open to suspicion are the lice, bed-bugs and fleas.

In 1909, Nicolle, Comte and Conseil, succeeded in transmitting typhus fever from infected to healthy monkeys by means of the body louse (_Pediculus corporis_). Independently of this work, Anderson and Goldberger had undertaken work along this line in Mexico, and in 1910 reported two attempts to transmit the disease to monkeys by means of body lice. The first experiment resulted negatively, but the second resulted in a slight rise in temperature, and in view of later results it seems that this was due to infection with typhus.

Shortly after, Ricketts and Wilder (1910) succeeded in transmitting the disease to the monkey by the bite of body lice in two experiments, the lice in one instance deriving their infection from a man and in another from the monkey. Another monkey was infected by typhus through the introduction of the feces and abdominal contents of infested lice into small incisions. Experiments with fleas and bed-bugs resulted negatively.

Subsequently, Goldberger and Anderson (1912_b_) indicated that the head louse (_Pediculus humanus_) as well, may become infected with typhus. In an attempt to transmit typhus fever (Mexican virus) from man to monkey by subcutaneous injection of a saline suspension of crushed head lice, the monkeys developed a typical febrile reaction with subsequent resistance to an inoculation of virulent typhus (Mexican) blood. In one of the three experiments to transmit the disease from man to monkey by means of the bite of the head louse, the animal bitten by the presumably infected head lice proved resistant to two successive immunity tests with virulent typhus blood.

In 1910, Ricketts and Wilder reported an experiment undertaken with a view to determining whether the young of infected lice were themselves infected. Young lice were reared to maturity on the bodies of typhus patients, so that if the eggs were susceptible to infection at any stage of their development, they would have every opportunity of being infected within the ovary. The eggs of these infected lice were obtained, they were incubated, and the young lice of the second generation were placed on a normal rhesus monkey. The experimenters were unable to keep the monkey under very close observation during the following three or four weeks, but from the fact that