Pathology of Laboratory Animals

PATHOLOGY OF LABORATORY ANIMALS (nosology) is very diverse in both its manifestations and anatomical changes. The pathology of guinea pigs, white mice and rats, and especially rabbits, has attracted the greatest attention from researchers. The diseases of dogs, cats and birds are also fairly well known. As for other laboratory animals, for example monkeys and mainly various cold-blooded animals, their pathology has been studied comparatively little at present, and for example, diseases of frogs are almost unknown, if we exclude several parasites of these animals with unclear pathogenic significance. A. Rabbits. Diseases of rabbits (with the exception of very rare ones) can be reduced to the following groups: diseases of bacterial origin (infectious rhinitis, pleuropneumonia, hemorrhagic septicemia, subcutaneous abscesses, pseudotuberculosis, spontaneous spirochetosis, etc.), a number of diseases caused by a filtering virus (rare), fungal diseases (scab, ringworm), diseases of protozoan nature (coccidiosis, infectious inflammation of the brain and spinal cord), helminthiases, diseases caused by mites (various types of scabies), various tumors and finally a large number of sporadic diseases, which also include all those diseases whose etiology and pathogenesis have not yet been studied. Of the listed rabbit diseases, infectious rhinitis deserves special mention—a very widespread disease in our rabbit breeding farms affecting the nose with subsequent involvement of the rest of the respiratory tract in the process ('malignant rhinitis'). This disease occurs most often in cold and humid seasons. Its etiology has not been sufficiently studied and at present there are reasons to consider this disease polybacterial. The disease first manifests as slight moisture around the nostrils as well as general signs of malaise, then abundant mucopurulent discharge from the nose, sneezing and significant emaciation. The course is acute or chronic (more often), but almost always the disease ends in death. Patho-anatomically, the disease is expressed mainly in inflammatory processes of the respiratory tract along with manifestations of various complications (inflammation of the middle ear, meninges and brain, subcutaneous abscesses, mainly in the head area, etc.). Diagnosis in pronounced cases presents no difficulties. Treatment, as well as preventive vaccinations, to date has not given practical results. Hemorrhagic septicemia—a fairly common disease caused by Bac. bipolaris septicus and most often ending in the death of sick animals after an acute (often lightning-like) or chronic course. Clinical manifestations are not characteristic: elevated temperature, general weakness, disorders of respiratory and digestive organs. Patho-anatomical changes are very characteristic (especially in acute cases), expressed mainly in hemorrhagic inflammation of the serous and mucous membranes of the organs of the chest and abdominal cavities, often accompanied by pleurisy and pneumonia of various nature and degree of severity, as well as significant enlargement of the spleen. The diagnosis is facilitated by the discovery in the blood of a specific microorganism in the form of a very small bipolarly staining bacterium. Treatment does not give any valuable results, and only ordinary preventive measures systematically carried out in farms make it possible to avoid the widespread spread of this deadly disease.--Pseudotuberculosis (see)—a chronic disease, often taking on a widespread distribution in rabbitries. The causative agent is Bac. pseudotuberculosis rodentinum, causing a similar disease among various rodents. Recognition of the disease during life is extremely difficult, therefore only strictly carried out preventive measures contribute to the cessation of epizootics in affected farms. Spontaneous spirochetosis—a chronic disease, very common among rabbits (other animals and man are not susceptible to this disease) and expressed mainly in the lesion of the genital area and the anus. Also known under the name 'genital disease' and 'rabbit syphilis'. Sometimes in farms spirochetosis affects almost all rabbits. The causative agent is Treponema cuniculorum. Transmission of infection occurs by direct contact between animals, mainly during sexual intercourse. The disease begins with edema and hyperemia of the mucous membranes of the affected areas, after which ulcers form on these places, covered with crusts. Subsequently, foci of warty dry growths appear in various areas of the skin (especially in the head area). The disease lasts for months, often ending in spontaneous healing, but sometimes relapses are observed. The infection is easily transmitted experimentally, with the incubation period lasting 3-12 weeks. Patho-anatomical changes are limited exclusively to the places of external manifestation of the disease. Diagnosis presents no difficulties due to the characteristic appearance of the lesions of the mucous membrane and skin and the easy detection by bacterioscopic means of spirochetes, which are usually found in significant quantities in the secretions of the lesions. Exceptionally good results are obtained from a single application of neosalvarsan (intravenously 0.06-0.09 per 1 kg of animal weight) or salicyl bismuth (intramuscularly 0.5-0.8 g of 10% oil emulsion per 1 kg of weight). Prevention consists in isolating sick and suspicious for spirochetosis animals, not allowing them to breed and thorough cleaning of cages. Subcutaneous abscesses ('wandering pyemia')—a fairly common disease in rabbits, expressed in the formation of one or several subcutaneous abscesses of various sizes with a white purulent or curd-like mass inside. In the latter, microorganisms (mainly staphylococci) are sometimes found. The disease often ends in spontaneous healing, relapses are often observed, but usually an untreated animal falls victim to secondary infections. Treatment consists in surgical intervention, which however is often difficult due to the multicameral nature of such abscesses.--Coccidiosis (see Coccidia)—the most common disease of rabbits, occurring in acute (mainly in young animals) or chronic form, characterized by high mortality and widespread distribution in affected rabbit breeding farms, where often all animals die in a short time. It can be considered that 85% of rabbits dying from all infectious diseases die from coccidiosis. The special danger of this disease lies in the fact that affected adult rabbits with their usual chronic course do not give characteristic symptoms, due to which for many years they are carriers of parasites, infecting the young. The course of the disease in young animals (usually up to 3 months of age) is distinguished by exceptional severity, and death sometimes occurs so quickly that it is not possible to detect any visible signs of the disease. Usually, the latter are expressed in diarrhea (in liver coccidiosis they are absent), polyuria, loss of appetite, severe weakness and emaciation, yellowish coloration of the mucous membranes; in acute cases, an increase in body temperature and often convulsions are also noted. Autopsy of carcasses of dead animals reveals in the liver form the presence in the liver of grayish-yellow nodules of various sizes; they are filled with a purulent mass containing a huge number of parasites. In the intestinal form, the main changes are found in the area of the small intestines: the mucous membrane is hyperemic, thickened, covered with mucus and often completely covered with white spots similar to semolina; in most cases the intestine is filled with gases. Treatment with various means, including numerous chemotherapeutic preparations, does not give practical results, therefore the destruction of coccidiosis rabbits is recommended to prevent the spread of epizootics. As complications, coccidial inflammation of the nasal mucosa and meningoencephalitis are noted.--Helminth invasions—see Rabbits. It is necessary to pay attention to the circumstance that experimenters using rabbits completely erroneously do not pay attention to the necessity of le-

PATHOLOGY OF LABORATORY ANIMALS

Rabbit scabies: this disease in all its manifestations cannot but affect the results of experiments with rabbits and often leads them to complete exhaustion and death from secondary infections (see Rabbits).--Tumors are observed mainly in old or very old rabbits (most often at the age of 6 years), which explains the relatively small number of cases of spontaneous tumors in these animals, which are rarely kept alive to the critical age. The most common site of tumor localization is the uterus (secondly--the kidneys). Epithelial neoplasms are observed much more often than tumors of connective tissue nature; among the former, glandular-epithelial tumors of the uterus are most common.--Traumatic diseases among rabbits are noted very often. These include various wounds inflicted constantly by rabbits on each other when kept together, with subsequent complications in their course, increased hair loss (mainly as a sign of metabolic disorders in the body), various digestive disorders under the influence of various irregularities in the keeping of rabbits (it should be noted in particular the often observed bloating of the abdomen by gases formed under the influence of fermenting feed in the digestive tract), elongation of the incisors due to insufficient grinding of teeth in the absence of coarse feed, "wet muzzle" (stomatitis vesiculosa), catarrh of the upper respiratory tract, sometimes very persistent conjunctivitis, often observed prolapse of the rectum, etc. B. Guinea pigs in relation to their P. are less studied than rabbits, and regarding the diseases observed in them, there are quite a few contradictory indications in the current specialized literature. A characteristic feature of P. of guinea pigs is the fact that some of their diseases proceed completely unnoticed by observers and end with spontaneous healing; on the other hand, these animals are distinguished by exceptional susceptibility to infectious diseases, which contributes to their widespread use for laboratory purposes, as well as explains the devastating epizootics, often observed in guinea pig nurseries. Spontaneous diseases observed in guinea pigs are currently known in a relatively small number (see Guinea pig). Infectious inflammations of the lungs--the most common diseases of guinea pigs, observed in nurseries mainly in cold and damp time of the year and lasting in the form of persistent epizootics for a very long time (often for years), then temporarily subsiding, then again exacerbating, until in most cases the entire stock perishes either from the disease or due to the cessation of reproduction of animals from significant weakening of the body by the same infection. The disease most often affects females at the end of pregnancy, often causing abortions or the birth of weak offspring, and usually ends in the death of the mother. The course in most cases is protracted, although acute infections are also common (especially among the young). Symptoms: weakness, difficult breathing, cough, more or less noticeable discharge from the nose, cyanotic coloration of visible mucous membranes, significant increase in t°, rales easily audible through the chest wall; the animal loses appetite, becomes less mobile, often groans, quickly weakens and then dies; cases of recovery are rarely observed. Path.-anat. changes: various stages of pneumonia, expressed more or less strongly (in young animals, rapidly dying from infection, the inflammatory phenomena are usually not sharply expressed), sometimes inflammation extends to the pleura; the right half of the heart is dilated, the myocardium is fatty degenerated, the liver usually has signs of fatty degeneration or resembles nutmeg. Attempts to treat infectious pneumonias in guinea pigs do not give positive results. Measures to combat these diseases should consist in prevention (not allowing guinea pigs brought from outside into the nursery without sufficiently long quarantine, possible early isolation of animals suspicious of the disease, etc.); with a significant size of the epizootic, the only rational measure should be considered the destruction of all guinea pigs of the affected nursery and their subsequent breeding (after carrying out appropriate measures) from fresh producers, which undoubtedly saves money, time and labor. Pseudotuberculosis is often observed among guinea pigs, in contrast to the very rare detection of cases of true tbc. In guinea pigs with poorly expressed clinical symptoms of pseudotuberculosis, the often observed paralysis of the hind limbs attracts attention (the simultaneous presence of lymphadenitis allows to differentiate this symptom from paralysis of other origin). Ante-mortem diagnosis: an antigen made from a culture of the pseudotuberculosis causative agent is injected into the skin after preliminary removal of the hair at this site, and after two days in case of a positive result, redness and swelling of the test site are detected. - Hemorrhagic septicemia (see above)--a similar disease in rabbits. - Paratyphoid diseases are often found in the form of "epizootics of guinea pigs and are caused by a microorganism identical with Bac. paratyphi B (cases of diseases with the causative agent from bacteria of the Hertner group have also been described). Clinical manifestations are most often expressed in diarrhea, vomiting, a significant increase in body t°, chills, rapid exhaustion. The course of the disease is acute (sometimes guinea pigs suddenly die without preliminary signs), or chronic. Path.-anat. changes: pronounced emaciation, effusion in the abdominal cavity, the spleen is significantly enlarged, as well as the mesenteric lymph nodes, the small intestines are hyperemic, their mucous membrane is swollen and with numerous hemorrhages, filled with mucous-liquid contents, sometimes there are signs of peritonitis; in the lungs, nodules of various sizes with caseous contents are found, sometimes fused with the pleura. Correct diagnosis is possible only by bacteriological means. A positive effect is sometimes obtained by the use of highly active paratyphoid serum, but usually only by appropriate preventive measures can devastating epizootics be avoided. - Paralysis are observed in guinea pigs as a symptom of various diseases (pseudotuberculosis, plague, hemorrhagic septicemia, etc.), as well as in the form of a special disease meningo-myeloencephalitis infiltrativa. The latter is expressed first in a paralyzed state of the hind limbs, rapidly growing weakness, tremors, shortness of breath, urinary incontinence, convulsions of the limbs. The disease ends after several days with the death of the animals. The causative agent has not been found, but the brain (cerebral and spinal) is a carrier of the virus, since the introduction of brain emulsion of sick animals into the body of healthy ones causes a similar disease in the latter. Path. changes in the bodies come down to sharp hyperemia of internal organs and especially the meninges. Avitaminoses--a common phenomenon among guinea pigs in the absence of green feed. They are most often observed in early spring and are expressed mainly in a significant depletion of the hair coat, paralysis of the hind limbs (one- or two-sided), a sharp weakening of the body, and the absence of the ability to reproduce. The transition with the onset of summer to fresh green feed, as well as intensive feeding of sick animals with vitamin-rich feed quickly eliminates such disorders. - Helminthiases and skin parasites--see Guinea pig. - Coccidiosis is often observed in guinea pigs (however, much less often than in rabbits), and more often the invasion is not accompanied by pathological disorders of the body, and only in young animals is it sometimes possible to observe in such cases diarrhea, loss of appetite, sharp emaciation and death in the presence of convulsions. The parasite--coccidia Eimeria caviae (Sheather, 1924), which does not invade other animals besides guinea pigs. Path.-anat. changes are expressed by the presence of yellowish nodules in the liver and hyperemia of the intestine (in young animals), in which coccidia are found (the thick and rectum).-Plague of guinea pigs--a rather rare disease, caused by a filterable virus, which is located in the brain. Symptoms: slow exhaustion of the body, before death, convulsions, difficulty breathing, convulsive movements, cyanosis of visible mucous membranes. Changes in the corpse are characterized almost exclusively by sharply expressed hyperemia of internal organs and meninges. - Tumors in guinea pigs are observed very rarely. The most common localization of neoplasms in them is the lungs (adenoma-like tumors), then the ovary (epitheliomas of the chorion, etc.) and the mammary glands (adenomas, lipomas, etc.). V. Rats until recently have attracted too little attention in the study of P. l. a. and therefore the number of diseases currently known in rats is insignificant. Pneumonia--one of the most common diseases of rats. The causative agent has not yet been established with accuracy.

Symptoms: loud, labored breathing, loss of appetite, drowsy state, sitting with a bent back, cloudiness of the eyes, paleness of the ears and tip of the nose, moist nostrils, the coat loses its gloss and smoothness. The course of the disease is usually acute, ending in death; in chronic cases, death of the animals occurs after several weeks. On autopsy, clearly expressed inflammatory phenomena are found in the lungs, along with other less characteristic pathological changes. Placing the animals in a warm place and enhanced feeding (warm milk with sugar, meat juice, administered into the animal's mouth using a glass pipette) often contribute to rapid recovery, but it is better to destroy sick rats to prevent the development of an epizootic. - Inflammation of the middle ear is observed quite frequently among rats. At the beginning of the disease, animals hold their head slightly to one side, then circular movements appear. The etiology is unknown, which is why the isolation of sick animals is recommended. - Avitaminoses are very common in rats. A deficiency of vitamin A in the animals' food is manifested by disorders in the growth of rats and inflammatory phenomena in the area of the eyes; with deficiencies of vitamin B, growth defects are also found along with symptoms of polyneuritis, similar to similar symptoms in humans; finally, a special vitamin E causes the inability to reproduce even in young sexually mature animals. Feeding with food rich in the corresponding vitamins brings the rats back to a normal state. Other, less frequently observed diseases of rats: pseudotuberculosis, paratyphoid disease, hemorrhagic septicemia, mange, a special leprosy-like disease (see Leprosy), tularemia (see), plague (see), bartonellosis (see Bartonella-Bartonella muris), etc. Diseases caused by animal parasites - see Rats. - Tumors in rats are observed very rarely, and they are found mainly in not-young animals (older than 1½ years). Most often, new growths were found in rats in the liver (in most cases sarcomas), then in the chest area (fibroadenomas, cancer), in the kidneys, followed by the stomach and other organs. - Elongation of the incisors in rats is observed particularly frequently (compared to other laboratory animals). Mice, in relation to their pathology, like rats, began to be studied only relatively recently. Paratyphoid diseases are one of the most frequent manifestations of the pathology of mice. The causative agent belongs to the group of bacteria, mainly Breslau or Hertner's group, along with very frequently found in mice paratyphoid group bacteria. The course of the disease and pathological-anatomical changes are similar to those observed in a similar disease of guinea pigs (see above). Combating the rapidly developing epizootic is possible only on the basis of preventive measures. - Other infectious diseases of mice: pneumonia, various types of septicemia, pseudotuberculosis (somewhat different in its causative agent from that observed in this disease in other rodents), colibacillosis, mange, etc. - Animal parasites - see Mice (attention should be paid to the wealth of species of these parasites found in mice). Tumors are observed in mice quite frequently, which distinguishes mice in this respect among all other laboratory animals. Females are predominantly affected by tumors, and at an age not younger than 6-8 months. As for the localization of new growths, modern statistical materials irrefutably prove the possibility of the occurrence of new growths in all organs and in all parts of the body. Finally, multiple and often different tumors are often found in mice. (See also Frog, Monkeys.)