Tick (parasite)

“ The next important step was taken in 1889 when Smith and Kilbourne conclusively showed that the so-called Texas fever of cattle, in the United States, is due to an intracorpuscular blood parasite transmitted exclusively by a tick. This discovery, antedating by eight years the work on the relation of the mosquito to malaria, had a very great influence on subsequent studies along these lines.
While much of the recent work has dealt with the true insects, or hexapods, it is now known that several of the most serious diseases of animals, and at least two important diseases of man are tick borne. ”

“ Symptoms of a successful infection by the tick appear in from five to seven days.
It would seem that the various insect transmitters act merely in a more or less mechanical way and that there is no essential biological relationship between the parasite and the transmitter, as is the case with the malaria parasite and the mosquito, or with the trypanosome and the tse-tse fly. The spirochæte is abstracted with the blood when the insect transmitter feeds ”

“ Think what a life-history this parasite has! Living in the blood-corpuscles of a dog, sucked up by an adult tick, passed through her body until it reaches an egg, laid with that egg, being present while the egg segments and slowly develops into the larva, living quiescent during the larval stage and the nymph stage, surviving the metamorphosis, and only leaping into activity when the adult stage is reached. This most remarkable story probably indicates that the Piroplasma undergoes a series of changes comparable to those of the malaria organism when it is inside the mosquito ”

“ The investigations made by the Bureau of Animal Industry demonstrate that the ticks which adhere to cattle from the infected district are the only known means of conveying the infection to susceptible cattle. The infection is not spread by the saliva, the urine, or the manure of cattle from the infected district. In studying the causation and prevention of this disease, attention must therefore be largely given to the tick, and it now seems apparent that if cattle could be freed from this parasite when leaving the infected district they would not be able to spread the malady. ”

“ Any tick now commonly infesting some wild animal, may, as its natural host becomes more uncommon, attach itself to some domestic animal. Since most of the hosts of ticks have some blood-parasites, the ticks by changing the host may transplant the blood-parasites into the new host producing, under suitable conditions, some disease. Numerous investigators throughout the world are studying this phase of tick-life, and many discoveries will doubtless signalize the coming years. ”

“ Ricketts showed that the reservoir of the virus was to be found in ground squirrels, chipmunks, mountain rats, etc., and that ticks feeding on these rodents become infected and transmit the disease to man. The guinea pig, white rat and monkey are also susceptible.
The virus can be propagated indefinitely in guinea pigs without loss of virulence by weekly blood inoculations in another animal. The virus seems to be transmitted by the salivary secretion of the tick and a tick once infected remains infective for the remainder of life. ”

“ Infection of another person may then occur from a subsequent bite by the infected tick, the virus not passing into the body from the salivary glands or mouth, but entering the wound after having been excreted by the attached tick. As occurs with the tsetse-fly carriers of sleeping sickness, only a part, in this case about one third, of the ticks feeding upon a person with relapsing fever become infected themselves. Of those which do, however, some may transmit the infection to their offspring, which are then capable of infecting man with the virus thus received. ”

“ After a varying time it also drops to the ground, undergoes a metamorphosis, and gives rise to the eight-legged adult tick. Here at last we reach the infective stage; the adult tick is alone capable of giving the disease to the animal upon which she feeds, and then only when she is descended from a tick which has bitten an infected host. ”

“ While given species of ticks show a preference for particular genera of animals, yet ticks generally in their vagabond life will leave the long grass and brush where they have been hatched to become temporarily the guests of any passing animal. It is, therefore, premature to seek to identify any single species of tick as the only bearer of the infection, and it is quite possible that any one of several species may contribute to its propagation. ”

“ Prophylaxis and Treatment
Prophylaxis.—The sole question is the avoidance of places infested with ticks, bedbugs and lice. In Africa, the habitations of the natives, where infected ticks may hide themselves in cracks in floors and walls, are to be especially avoided. As the tick feeds at night a night light is of value.
Destruction of the spirochaetes by salvarsan injection is important prophylactically as well as therapeutically—the reservoir of infection for lice or ticks being gotten rid of. ”

“ Natives seem to suffer severely from tick fever in childhood but in adult life possess a sufficient degree of immunity so that the disease shows itself in a very mild form in those harboring spirochaetes.
The immunity conferred by an attack is not lasting and a second infection may occur within a year. Such second attacks, however, do not present the relapses so important in a clinical diagnosis. As a matter of fact there may be no symptoms and such cases with spirochaetes in their blood make ideal carriers for the infection of ticks or lice. Ticks can be infected by these carriers. ”

“ The wood ticks are familiar to inhabitants of uncultivated lands, and prove troublesome parasites to man and beast alike. The tick lives on bushes, and attaches itself to the mammal only to secure a feast of blood, for when gorged it drops off to sleep off its debauch on the soil. The tick produces great irritation by boring into the skin with its armed proboscis. If pulled out, the head and thorax are often left in the skin. They may be covered with oil to shut out the air from their breathing pores, or by touching them with a hot penknife they will be impelled to let go their hold. ”

“ The parasites are not hereditarily transmitted in Rhipicephalus, but when taken by the transmitter at one stage of its development the tick is infective in its next stage (e.g., if the larva becomes infected, then the nymph is infective; if the nymph becomes infected, then the adult is infective) .
An animal recovered from Theileria parva is incapable of infecting ticks, but few animals recover from East Coast fever. Animals suffering therefrom do not show hæmoglobinuria. ”

“ Again, animals may die from distemper or be eaten up with lice or troubled with itch or mange—you will note these facts as you go along with your work.
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In the South, where Texas fever is so prevalent, you should look for ticks, as these bring death to thousands of animals each year. Look for the wee tiny ones—they cause the trouble. When cattle are fairly covered with the large ticks death does not ordinarily follow, since the animal has practically become immune to the poison caused by the tick. ”

“ Hooker, Bishopp and Wood (Bull. 106, U.S. Dept. Agric., Div. Ent., 1912, p. 189) state that a number of cases have been brought to their notice where the bite of this tick has caused considerable local inflammation, which in some cases required physicians’ attention. It has been supposed to be connected with Rocky Mountain spotted fever, but it is doubtful if it is concerned in its transmission. The engorged female is steel grey, the dorsum with an olive-green surface colour, which covers the grey except in small spots, giving a mottled appearance. ”

“ It was found that the southern cattle in the region where the ticks occur normally, usually have a mild attack of the disease when they are young and although they may be infected with the [Pg 31] parasite all the rest of their lives it does not affect them seriously. These cattle are almost always infected with ticks, and when taken north where the ticks do not occur naturally and where the cattle are therefore non-immune, some of the mature ticks drop to the ground and lay their eggs which in a few weeks hatch out and are ready to infect any animal that passes by. ”

“ Lyme disease is a potentially debilitating bacterial infection, transmitted to humans by the bite of a very small tick, that merits the attention of all Americans. These ticks—which frequently appear to be no larger than a freckle—feed primarily on deer, but other hosts may include horses, dogs, cats, birds, and cattle. Although most cases are concentrated in the coastal Northeast, Wisconsin, Minnesota, northern California, and Oregon, Lyme disease has been reported in nearly all States, and the number of recorded cases has been increasing each year. ”

“ All infective disease of sheep, inoculated by ticks, and producing a meningo-myelitis, with drowsiness, hyperæsthesia, irritability, paresis and other nervous disorders.
Animals susceptible. This is almost exclusively a disease of sheep, yet Meek and Greig-Smith claim to have seen it in swine that have eaten the raw carcasses of louping-ill sheep, or that have ranged the tick infested pastures, and in rabbits inoculated with the microbe from the wound caused by the tick. W. Williams claims to have seen well marked cases in cattle, and heard of cases in horses and swine. ”

“ The ticks differ from the insect bearers of disease inasmuch as the tick that attacks an ox or a dog does not itself convey the disease, but it lays eggs—for I regret to say here, as with the Anopheles, it is the female only that bites—and from these eggs arises the generation which is infective, and which is capable of spreading the disease. The tick which conveys the Piroplasma from dog to dog is called Hæmophysalis leachi. The brilliant researches of Mr. Lounsbury have shown that even the young are not immediately capable of giving rise to the disease. ”

“ The species which are of particular interest to the human pathologist are Ornithodoros moubata, O. savignyi, Argas persicus, and Dermatocentor venustus— the first two being the transmitters of tbe spirochæte of African relapsing fever; the third, of the spirochæte of the miana disease (Balfour) . It is quite likely that other species will in the future ba found to be concerned in the transmission of disease germs to man. Important animal diseases due to Spirochœtœ and Babesiœ are also known to have tick transmitters. ”

“ This form of tick disease is manifestly different from Rocky Mountain fever, as it is non-febrile, is unattended with eruption, and is not communicable by inoculation. Possibly it is produced by a poison instilled by the'tick during haustellation. The wound it makes is very painful, is attended with œdema and, on forcible removal of the tick, with free bleeding as if some anticoagulin had been introduced. In sheep the favourite points of attachment of the tick are on the back along the course of the spine; in man, the nape of the neck. ”

“ It is called bibo in Uganda, moubata in Angola, and tampan on the Lower Zambesi. It feeds on animals and birds as well as man. Its bite is very painful. This tick is found in native huts, living in cracks and crevices and in the thatch roofs.
The female tick infected with the spirillum transmits the infection to the eggs and the next generation. They appear to be able to live without food a long time, and probably live for years. They lay their eggs in masses on the ground or in crevices, and when they hatch they are in the nymph stage with four pairs of legs. ”

“ Ticks should also be carefully exterminated, as they are sometimes responsible for such diseases as Rocky Mountain spotted fever, African tick fever, and other infections. The bedbug is also by no means the harmless creature which it is generally regarded. ”

“ Because Lyme disease can pose a significant health threat, and because no completely reliable test for detection of the infection has been developed, prevention is very important. Hikers, outdoor workers, and other individuals who enter wooded, tick-infested areas should take precautions to avoid being bitten by the deer tick. These include staying away from long grass or brush, covering up well with light-colored slacks and long-sleeved shirts, using tick repellents, and carefully examining oneself afterwards for ticks. ”

“ But the end is not even yet, for these same animals often suffer from diseases similar to those of man and like them transmissible through or carried by insects. Ticks are not insects, but the economic entomologist is often expected to deal with them, hence we may just mention the cattle tick in connection with Texas fever, which has destroyed and still destroys its thousands and causes enormous money losses. ”

“ This tick seems to prefer the crevices and open joints of bamboo beds, laying its eggs and moulting in the hiding places. It comes out at night to feed on the occupants of the bed. Two white rats were inoculated with an emulsion made from ticks taken from a suspected bed. Both rats developed a spirochaete infection. A man inoculated with blood of one of these rats developed relapsing fever on the sixth day. A second man was inoculated subcutaneously with an emulsion of ticks collected from a bed and showed spirochaetes in his blood on the eleventh day. ”

“ General measures along the line of tick eradication must be carried out if the disease is to be controlled. That such measures are feasible has been shown by the work which has been done in controlling the tick-borne Texas fever of cattle, and by such work as has already been done against the spotted fever tick, which occurs on both wild and domestic animals. ”