Respiratory Parasites of Dogs and Cats Presentatio

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Respiratory Parasites of Dogs and Cats


Life cycle diagram Paragonimus is a trematode that may inhabit the lungs of a variety of mammals. Paragonimus kellicotti is the species of importance to domestic animals in the U.S. Like most flukes, the adult stage is not highly host specific and P. kellicotti may be found in a number of mamma1ian definitive hosts. The mink is regarded as being the usual final host in the U.S. but a large reservoir for this parasite exists in other wild animals (including the muskrat, oppossum, raccoon, skunk, bobcats, fox and others). Paragonimus is therefore considered to have a primarily sylvatic epidemiologic cycle in which dogs, cats and rarely, the pig may become infected as “secondary” or “accidental” hosts. Louisiana and the Great Lakes area have a high incidence of wild animal infection but P. kellicotti has been reported from most states in the Eastern half of the U. S. The life cycle involves a snail intermediate host and a crayfish second intermiate host. Another species, Paragonimus westermani (Oriental Lung Fluke) is a serious parasite of man in the Orient. Paragoniums kellicotti


Adult flukes in the lung release operculated eggs into the bronchial tree which are subsequently coughed up, swallowed and shed in the feces. Paragonimus egg Paragonimus eggs are yellow to brown in color, 80-118 by 40-65 M in size and have an operculum set into a characteristic col1ar-like thickening.


After 2-3 weeks development within eggs in an aquatic environment, short-lived, ciliated miracidia emerge which must find a suitable snail intermediate within 24 hours or perish. Paragonimus kellicotti Miracidia


In the U.S., amphibious snails (Pomotiopsis spp.) serve as the first intermediate host. Snail intermediate host


Miracidia initiate a complex asexual reproductive phase in snail tissues and produce large numbers of free swimming cercariae. P. kellicotti redia


Cercaria. Cercariae penetrate through the exskeleton of the crayfish second intermediate host, encyst as metatacercaria and await ingestion by the final host. Crayfish(Cambarus spp.) A number of species of crayfish in the U.S. may serve as second intermediate hosts.


Metacercariae become infective to the final host in a period of several weeks. An immature fluke is present within the cyst wall at this time. Metacercaria in crayfish heart muscle


After ingestion, metacercariae excyst in the intestine, young flukes penetrate the gut wall into the peritoneal cavity and then migrate across the diaphragm to the p1eura1 cavity. They migrate in lung tissues for 3-4 weeks before pairing up cysts which are radiographically visible 4 weeks after infection. Mature flukes are found in fibrous pulmonary cysts 5 to 6 weeks afer infection at which time patency occurs. Definitive host


Cysts of Paragonimus are usually found close to the lung surface and appear as nodular elevated masses of 1-2 cm beneath the pleura. Migration of young flukes through thc pleura is sometimes marked by small hemorrhages which progress to small scars. P. kellicotti lung cysts


During migration through the lung parenchyma, young flukes pair up and are generally found with two adults within individual cysts. Paragonimus are small, thick flukes, are reddish-brown in the living state and measure 1 by 11/2 cm. P. kellicotti lung cysts


Adult parasites are often found in what appears to be a greatly dilated bronchiole surrounded by reddish fluid containing fluke eggs and cellular debris. A patent fistulous communication to the bronchial tree is present for passage of eggs. Eggs may escape to lung tissues and cause granulomatous inflammation, particullarly where there is no communication for escape of eggs to the bronchio1es. Eggs sometimes find their way into thc general circulation and are fi1tered out in the major capillary beds, inciting small foci of granulomatous inflammation in other areas of thc body. Paragonimus adults in cross section and microscopic in canine lung


Infections may be diagnosed by finding the very characteristic eggs using routine fecal flotation procedures. (Eggs of many fluke species sink in flotation media). Eggs can also be readily detected by tracheal swabs or tracheal washes. Diagnosis may also be made by radiography, particularly when eggs are not being passed. Cysts are seenas circumscribed pulmonary soft tissue densities. On rare occasions, cysts are contained in a radiolucent area (an air bubble in the cyst). This “signet ring” morphology, when it occurs, is patbognomonic of Paragonimus. Paragonimiasis is usually manifested clinically by relatively mild respiratory distress and a persistant hacking cough. Lung sounds are often normal unless many flukes are present and the pleura is involved. In heavy infections, the exertion will initiate a coughing seizure. Signs are likely to be more severe during the migratory and growth phase as flukes establish themselves. Hemoptisis is sometimes seen at this stage. Fatal cases have been reported due to pulmonary hemorrhage or secondary infection following simultaneous entry of a number of flukes into the lungs. Pneumothorax may occur if subpleura1 cysts rupture. Diagnosis


Treatment Fenbendazole and albendazole are effective at the level of 25 mg/kg BID for 14-21 days. Praziquantel reprted to be effective at 25 mg/kg TID for 2 days. Bithionol no longer manufactured. Nodular radiographic leasion resolve within 2 months after successful therapy.


There are three species of nematode lungworms in the genus Filaroldes (Family Metastrongylidae) which infect dogs: Filaroldesosleri, F. milksi, and F. hirthi. All are of relatively low incidence and are generally considered to be of low pathogenicity. The life cycle for Filaroides spp. is unique in being infective at the L1 stage. It is thus directly infective when passed in feces or sputum. Life cycle possibly evolved for transmission via fecal-oral route or by regurgitated food by carnivores in neonatal period. Filaroides


F. osleri resides at the bifurcation of the trachea in elevated wartlike granulomatous nodules. The worms are small in size (0.5 to 1.5 cm in 1ength) and several are usually present in each nodule which has a medusa head appearance when worms are extracted partially. Lesions are covered by columnar epithelium and ovoviviparous female worms release larva forms through “pores” in the mucosa. Females deposit larvae encapsulated by a single shell membrane which hatch immediately, move up the trachea, and are then swallowed. Infected dogs may have a persistant, harsh cough, especially after exercise, and sometimes have gradual emaciation and loss of condition. Litters of pups typically develop signs of disease after 10 weeks post-partum. Filaroides osleri


F. osleri diagnosis is made by finding larvae by fecal examination or by trachea swabs. Large lesions may be visible radigraphica1ly, ZNSO4 (sp. gr. 1.18) flotation if 100 x thc accuracy of Baermann. The larvae may be differentiated from other parasites (ea. Strongyloides stercoralis) by tbc presence of an S-shaped notch in the tail. Direct bronchoscopic examination of nodules or radiography may also lead to a diagnosis. Notch tailed larvae


These species occur in the lung parenchyma in lesions that are evident as blister-like granulomatous foci beneath the pleura or as scattered foci through deeper lung tissues.Tissue reaction occurs due to congregated nests of adult and larval forms. Infections are generally regarded as asymptomatic, although fatal granulomatous pneumonia has been reported. F. hirthi has been recently described as a separate species following a 1973 report of 40% asymptomatic incidence in a commercial beagle colony in New York. (Hirth and Hottendorf Vet. Path. 10:385). This parasite may become endemic in kennels, reducing the value of animals (I.E. beagles) for toxocologic trials and other experimental uses because of the pathology seen. F. hirthi and F. milksi


Effective treatment for Filaroides spp. has not been established. F. osleri F. or F. osleri, oxfenbendazole (10 mg/kg for 28 days) and ivermectin (400 mg/kg) are reported to be effective. Beagle colonies may be freed of F. hirthi infection by ABZ treatment of breeding animals and hand-raising caesarian-derived pups. Treatment and Control


Aelurostrongylus abstrusus causes a chronic respiratory disease in cats which is unresponsive to antibiotic therapy and characterized by coughing and sneezing. In severe cases spasms of coughing, dyspnea and progressive wasting are seen. The adult worms reside deep in the lung parenchyma in the termina1 bronchioles and alveolar ducts. Aelurostrongylus abstrusus Cat host


Eggs are non-embryonated when laid by adults in the lungs. After embryonation in alveoli the first stage larvae batch and attempt to ascend the bronchiolar tree. First stage larvae are coughed up, swallowed and pass in the feces. Continual development occurs after infection of the intermediate host, the snail or slug, and most often gain entry to the cat definitive host after ingestion and encysted larvae in one of several paratenic hosts. Aelurostrongylus abstrusus Life cycle


Notch-tailed larva-Aelurostrongyus These notch-tailed larvae can survive in moist soil for up to 51/2 months.


Several, genera and species of moluscs can serve as true intermediate hosts. The first stage larvae actively penetrate the foot of the molluscs and develop to infective third stage larvae. Infective larvae remain viable in snails for as long as 6 months . Slug intermediate hosts


Paratenic host Cats can become infected after ingestion of molluscs containing lungworm larvae, but this probably happens only rarely. Transport or paratenic hosts which feed upon molluscs (including rodents, amphibians, reptiles and birds) serve as the principle source of infection for cats.


The most typical gross lesions are subpleural greyish nodu1es that project slightly above the surface of the lungs. The nodules may vary from pin point to 10 or more mm’s in diameter. In severe cases lesions may coalesce to form larger areas of consolidated tissue. A. abstrusus Gross lesions


The presence of worms, eggs or larvae in bronchioles and alveolar ducts is associated with an inflammatory exudate, hyperplasia of the bronchiolar epithelium and hyperttrophy of hypertrophy of peribronchiolar glands. If a nodule is incosed, a small amount of creamy exudate containing numerous eggs and larvae as well as neutrophils, eosinophills, lymphocytes, plasma cells, and giant cells is expelled. Histological lesions


Hypertrophy of smooth muscles in walls of bronchio1es and alveolar ducts occur early in the course of the infection and is progressive. Muscular hyperp1asia of pulmonary arteries begins later in the course of the infection (at about the 4th week). The medial layers of many vessels become 3 to 12 times thicker than normal. This change is not specific, however, and occurs in other conditions in the cats each as ascarid migration and feline dirofilariasis. Although signs of parasitic pneumonia regress after the 4th month of infection, the arterial hypertrophy and hyperplasia 1argely remain for 2 years and may persist for the lifetime of the cat. Histological lesions


Most affected cats show litt1e clinical disturbance, but whether because of heavy infection or decreased resistance, a few exhibit definite illness that occasionally results in death. Clinical Signs


Typical signs of illness include a chronic cough with gradually increasing dyspnea, inanition, anorexia, and fever. Lung sounds include harsh or moist ra1es. Occasionally there may also be sneezing and oculonasal discharges. The disease tends to be self-limiting and the most dangerous period is 6 to 13 weeks after infection when great numbers of eggs and larvae are produced. In very severe infections the simultaneous disposition of a large number of eggs in the lungs may cause sudden death. Outward signs and passage of first stage larvae in the feces may cease within 2 to 3 months and recur when the cat is subjected to stress. There are no age, sex, or seasonal variations. Clinical Signs


Diagnosis Clinically, cats exhibiting a chronic cough (perhaps accompanied by gradual weight loss) that is unresponsive to antibiotic therapy should be considered suspects for lungworm infection due to Aeleurostrongylus . Eosinophilia may be seen, but many other diseases, including other respiratory diseases, may be accompanied by eosinophilia.


Fecal examination for the characteristic notched or S-shaped tail of first stage larvae is the most accurate and practical diagnostic technique. A. abstrusus larvae are 360-400m in length and commonly are coiled upon themselves. Methods available are the direct smear, fecal flotation, and the Baermann method. The direct smear is the least accurate, as the irregularity of larvae passage and the size of the sample tend to be limiting factors. The flotation method is more accurate, but certain limitations must be considered. Because of the high osmotic pressure, concentrated salt solutions draw so much water out of the larvae that the specific gravity of the larvae becomes greater than that of the salt solution so that the larvae tend to shrivel and sink. With sugar solutions, the viscosity of concentrated so1utions reduces the speed of flotation of the larvae. For short periods (5 minutes or less) of flotation, a 50% sataurated solution floats most larvae, but if enough time (8 minutes or more) is allowed, saturated sugar solution floats the greatest number of larvae. The Baermann method has been found by most to be the most accurate. A simplified Baermann-type procedure can also be used-i.e. , feces are placed in a dish containing a little water. The larvae will migrate from the feces into the water which can be examined microscopically after approximately 1 hour .


The active period when larvae are found in the feces usually lasts about 2 to 3 months and rarely over 2 years. Fecal examination will not reveal early infections (less than 5 to 6 weeks) when adults are not yet mature, nor late infections when worms are no longer laying eggs. Trachea swabs may also be used to recover larvae. Diagnosis


Aelurostrongylosis tends to be se1f-limiting and demonstrable immunity develops. Good supportive therapy and care may suffice in mild or longstanding cases. L-Tetramizole has been tried by various investigators but only causes temporary reduction in larvae production. Ivermectin ( 400 µg/kg) and fenbendazole (25 mg/kg BID for 1 week) are reported to be effective. It appears from experimental evidence that administration of small doses of infective 1arvae on several occasions protects cats from a massive challenge for at least a year. Persistence of immunity is likely to be related to persistence of adult worms in the pulmonary tissues. Treatment


Capillaria oerophila - histosection canine lung Capillaria aerophila The Fox Lungworm


Capillaria oerophila is a member of the Family Trichuroidea and is closely related to the whipworm, Trichuris. Adult lungworms are 1.5 to 4 cm in length and inhabit the trachea, bronchi, and bronchioles of dogs, foxes, and cats. The life cycle is direct ( no intermediate hosts are required) although earthworms are reported to serve as transport hosts. The eggs bear a close resemblance to those of the dog whipworm, Trichuris vulpis and are passed in the feces after being coughed up from the trachea and swallowed. Eggs are quite resistant to cold and other adverse conditions and develop to the infective stage on the ground in 5- 7 weeks. After ingestion by the definitive host they hatch and migrate via the bloodstream in 7-10 days and become mature about 40 days after infection. Differentiate from C. boemii (nasal capillariasis) in dogs. Capillaria aerophila


In cats, differentiate eggs from Capillaria putorii a non-pathogenic intestinal species of smaller egg size (<66x28u). C. aerophila are confusable with Trichuris but can be differentiated by its slightly smaller size, paler color , roughened shell and blunt ends. Capillaria aerophila is most common in young animals and occurs especially in outdoor dogs such as hounds. Light infections are asymptomatic but heavy discharge and progressive debility in association with bronchitis. Infection is often much more severe in foxes.


FBZ or ADZ at 25 mg/kg BID for 14-21 days or ivermectin (600mg/kg) reported to be effective. Control consists of the same rigid sanitation in kennels necessary to prevent whipworm and roundworm infections. Treatment


Linguatula serratais a member of the Phylum Pentastomida (Tbe Pentastomes). It is a rare parasite found in the nasal passages and frontal sinuses and sometimes the eustachian tube and inner ear of dogs and related carnivores. Linguatula is a blood sucker and causes no clinical signs in many cases. In others there is sneezing, bleeding, dyspnea, and inflammation. Eggs pass in nasal discharges and are ingested by one of a variety of herbivorous animals, especially rodents which serve as intermediate host. The nymph stage has a very low host specificity. Nymphs develop in the mesenteric lymph nodes, liver or other tissues where they await further development after ingestion of viscert by the final host. Infected ruminants are thought to be the most common source of infection for dogs. The life cycle may be completed in approximately six months. Linguatula serrata (tongue worm)


Linguatula serrata in situ.


Diagnosis of Linguatula is made by finding larvated eggs in nasal discharges or by direct examination of nasal passages with an otoscope. The organism is elongate, flattened and have a series of conspicious body rings. They attach firmly to the mucous membranes by two pairs of retractable hooks on either side of the mouth. L. serrata removed


Anterior hooks and the characteristic morphology listed above distinguish Linguatula from other parasites. Linguatula has a longevity of 2 years and are then passed. Surgical removal is the only known treatment. L. serrata anterior hooks


The mite Pneumonyssoides caninum is infrequently found in the nasal sinuses of dogs. No signs are observed except perhaps a catarrhal rhinitis. Pneumonyssoides caninum (nasal mite)

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