VETERINARSKI ARHIV 69 (5), 279-287, 1999

ISSN 1331-8055 Published in Croatia

Incidence and regional distribution of the lungworm Aelurostrongylus abstrusus in cats in Croatia

Zeljko Grabarevic¹, Stipica Curic¹, Ante Tustonja², Branka Artukovic¹, Zoran Šimec¹, Kristijan Ramadan¹, and Tanja Zivicnjak³

¹Department of General Pathology and Pathological Morphology,
Faculty of Veterinary Medicine, University of zagreb, Zagreb, Croatia

²Veterinary Station Krapina, Krapina, Croatia

³Department of Parasitology, Faculty of Veterinary Medicine,
University of Zagreb, Zagreb, Croatia

* Contact address:
Prof. Dr. Zeljko Grabarevic,
Department of General Pathology and Pathological Morphology, Faculty of Veterinary Medicine, University of Zagreb, Heinzelova 55, 10000 Zagreb, Croatia;
Phone: 385 1 23 90 313; Fax: 385 1 244 13 90; E-mail: zgrabar@vef.hr

GRABAREVIC, Z., S. CURIC, A. TUSTONJA, B. ARTUKOVIC, Z. ŠIMEC, K. RAMADAN, T. ZIVICNJAK: Incidence and regional distribution of the lungworm Aelurostrongylus abstrusus in cats in Croatia. Vet. arhiv 69, 279-287, 1999.

ABSTRACT

Lungworm Aelurostrongylus abstrusus is a cat's lung parasite with an indirect life cycle. Its predominant sites are terminal bronchioles and alveolar ducts. In the study, two populations of cats were examined. The first group consisted of feral cats (N=50) in the rural areas of the County of Zagorje (northwest Croatia), while the second group included cats from the urban area of the City of Zagreb. For the second group, data were collected from faecal examination (N=529) from the Department of Parasitology and the gross and histopathological findings of cats' lungs (N=128) at the Department of General Pathology and Pathological Morphology of the Faculty of Veterinary Medicine, Zagreb. In the first group, histopathological examination was carried out and the Ae. abstrusus was diagnosed in 22% (N=11); in the second group, Ae. abstrusus was diagnosed in 0.38% (N=2) of the faecal examinations in the eight year period (1990-1998) and 3.9% (N=5) on histopathological examination of cats' lungs, also in the same period. Histopathological examination showed alveoli, bronchiole, and alveolar ducts filled with eggs and larvae of Ae. abstrusus, disruption of alveolar septa, cellular infiltrate (mostly eosinophils, macrophages, lymphocytes and few multinucleated giant cells), peribronchial cell infiltration, and a striking hyperplasia and hypertrophy of smooth muscle, i.e. medial layer, of the pulmonic arteries.

Key words: cats, lungworm, Aelurostrongylus abstrusus, incidence, Croatia

Introduction

Lungworm Aelurostrongylus abstrusus is a member of the family Metastrongylidae with an indirect life cycle that invades lungs of the cat, especially terminal bronchiole, alveolar ducts and alveoli. Its distribution is worldwide (Hobmaier and Hobmaier, 1935; Mackenzie, 1960; Hamilton, 1966; Gregory and Munday, 1976; Coman et al., 1981; Epe et al., 1993; Schuster et al., 1997; Tustonja, 1999) with a different frequency ranging from 1.1% (Epe et al., 1993) to 39.2% (Gregory and Munday, 1976). Concerning the parasitology of the parasite it should be noted that the cats become invaded after ingestion of a third stage larvae. Larvae travel to their final sites via the blood stream or via migration through the peritoneal and pleural cavity, something which is not completely understood. After a pre-patent period (5-6 weeks), first stage larvae are found in the faeces. They enter snails or snagsfoot tissue where they moult twice without cuticle shedding. Two to five weeks are essential for the two-sheets-enclosed larvae to be infectious for the cat. As it is unlikely for the cat to eat snails, paratenic vectors (frogs, lizards, rats, birds) are essential for further life cycle of Ae. abstrusus (Bowman and Lynn, 1995).

Since there is no report on incidence and regional distribution of aelurostrongylosis in cats in Croatia, the purpose of this report is to describe its frequency and histopathology of Ae. abstrusus in rural and urban areas of Croatia, and to compare results between these two groups of cats, as well as with similar results in Europe.

Materials and methods

The first group (A) consisted of fifty domestic, shorthaired male and female sexually mature cats from a rural area of the County of Zagorje. Cats were from a shelter, without owners and were to be euthanatized. Data from the second group (B) were collected from two sources. Firstly, the results of faecal examination (B1) from the Department of Parasitology, Faculty of Veterinary Medicine in Zagreb, which included faecal examination (N=529) from cats in an eight-year period (1^st January 1990-31^st December 1998) and secondly (B2), the criterion for inclusion into this study were records from a gross and microscopic lung examination from cats (N=128) examined at the Department of General Pathology and Pathological Morphology in the same period (1990-1998). Faecal examination was conducted using flotation method with saturated NaCl solution. In group A, after sedation and euthanasia with tiopenthal, cats were examined macroscopically and tissue samples for microscopically examination were fixed in neutral buffered 10% formalin, embedded in paraffin, sectioned at 5 µm and stained with hematoxilin and eosin (HE).

Results

In group A, pathohistological examination revealed aelurostrongylosis in 11 cases (22%) and of these 11 cats gross lesions were seen in 8 animals (16%), or 73% of histologically identified aelurostrongylosis. Faecal examination (group B1) revealed Ae. abstrusus in only 2 (0.38 %) cases of 529 examinations. In group B2, from 128 cats' lungs that were examined (macroscopically and microscopically), aelurostrongylosis was diagnosed in 5 cases (3.9%). In all 5 cats aelurostrongylosis were identified both microscopically and macroscopically. Gross lesions varied considerably according to the duration of invasion and consisted of discrete ecchymoses, white miliar disseminated foci in the lungs, white focal subpleural areas 1 to 2 mm in diameter and palpable numerous small, hard nodules that were placed deep in the parenchyma of the lungs. Microscopically, alveoli were filled with eggs and larvae of Ae. abstrusus with a disruption of alveolar septa (Figs. 1 and 2). These areas were surrounded by thick mononuclear cellular infiltrate with a few gigantocytes. In a few heavier infections this infiltrate is numerous because of dead and disintegrating larvae (Fig. 3). Necrosis and calcification (Fig. 4) were observed in a very few cases. In the early stages, eosinophils and neutrophils infiltrate were predominant. Lymphocytic nodules were formed around the blood vessels and airways. In more advanced cases diffuse thickening of septa because of fibrous and muscle tissue proliferation was observed. In most cases hypertrophy and hyperplasia of smooth muscle tissue in arteries, bronchioles and alveolar ducts were noted (Fig. 5).

Fig. 1. Alveoli of cat filled with embryionated eggs and larvae of Aelurostrongylus abstrusus surrounded by mononuclear infiltrate.
HE; 20×2.5; scale bar=20 µm.

Fig. 2. Intra-alveolar larvae of the parasite Aelurostrongylus abstrusus.
HE; 40×2.5; scale bar=10 µm.

Fig. 3. Dead parasite Aelurostrongylus abstrusus in the bronchioles.
HE; 20×2.5; scale bar=20 µm.

Fig. 4. Dystrophic incalcination and mixtocellular bronchiolar infiltrate in a cat infested by parasite Aelurostrongylus abstrusus.
HE; 20×2.5; scale bar=20 µm.

Fig. 5. Smooth muscle hypertrophy of the pulmonary blood vessels in a cat infested by parasite Aelurostrongylus abstrusus.
HE. 10×2.5; scale bar=40 µm.

Discussion

The study has shown that there is considerable incidence variation in appearance of Ae. abstrusus in rural and urban areas in Croatia. This is in accordance with studies conducted elsewhere in Europe (Coman et al., 1981; Epe et al., 1993; Schuster et al., 1997). This difference could be explained by the life cycle of the parasite: intermediate (paratenic) host plays a major role in transmission of the parasite. Since feeding habits are quite different (urban cats are fed predominantly with commercially available food, and not by means of predation, which is the case in a rural environment) frequency is also different. For faecal examination, material was predominantly from the urban areas of Croatia, and although the Baermann technique was not performed (Coman et al., 1981), which is supposed to be the method of choice for the identification Ae. abstrusus, the flotation method used in the study is quite reliable and should be the best method for identifying this lungworm. The reason we did not obtain a similar incidence in the B1 and B2 groups is probably the consequence of the intermittent expulsion of larvae. This probably resulted in very small incidence of parasite in the faeces.

Clinical symptoms are described in numerous studies (Dubey et al., 1968; Willard et al., 1988; Penniisi et al., 1995). It has been shown (Hamilton, 1967) that the severity of clinical symptoms and pathological findings depends directly on the amount of the ingested larvae. Experimental infection with 50 larvae provoked no clinical symptoms; 800 larvae caused respiratory symptoms, and 1600-3200 larvae caused severe or lethal infection. In naturally occurring infections clinical symptoms may be absent or infection may be characterised through mucopurulent nasal discharge, dyspnea, and polypnea. In one case, pleural effusion was associated with aelurostrongylosis in the cat (Miller et al., 1974).

Diagnosis of aelurostrongylosis is based on haematological values: decreased serum albumin concentration and increased number of nucleated red blood cells (Willard et al., 1988), although leukocytosis, lymphopenia and eosinophilia are also noted (Hamilton, 1967; Penniisi et al., 1995). Serum electrophoresis was evaluated and is found not to be a valuable diagnostic tool (Barsanti and Hubbell, 1980). Although cats with aelurostrongylosis display radiographic evidence of pulmonary infiltration, increased alveolar density, large main pulmonary artery, and changes in pulmonary vasculature (Willard et al., 1988), radiographic changes are suggestive rather than diagnostic. Transtrachel wash may reveal eosinophils and larvae in exudate. Baermann faecal examination is the most sensitive and specific clinical test for diagnosis of aelurostrongylosis (Willard et al., 1988), although it must be stressed that presence of larvae in faeces is not a constant feature and may give false negative results (Barsanti and Hubbell, 1980).

In group A, of the 73% of histologically diagnosed Ae. abstrusus, parasites were also noted macroscopically. This could be due to fact that at the onset of the course of the disease gross findings are discrete (Stockdale, 1970) and could be overlooked. Also, the histopathological diagnosis, although very useful and accurate in a diagnosis of aelurostrongylosis, has certain limitations (Willard et al., 1988). The lack of specificity was attributed to an inability to detect an active infection, or other disease that caused a similar lesion and microscopic examination in areas of the lungs that did not contain the worms. Our histopathological and gross findings are similar to those previously described (Mackenzie, 1960; Hamilton, 1966; Hamilton, 1966a; Dubey et al., 1968; Hamilton, 1968; Stockdale, 1970; Penniisi et al., 1995). An interesting finding is hypertrophy and hyperplasia of smooth muscle in airways and blood vessels. The pathogenesis of this event is not fully understood. According to one study (Stockdale, 1970) hypertrophy and hyperplasia of smooth muscle was noted 17 days post-experimental infection. Because such changes are recognisable in the early course of the disease, it is not acceptable that toxic substances from parasite are the main cause. Furthermore, such a toxic substance was never isolated. There are many other theories (hypoxia, airway obstruction, neural, humoral and myogenic origin, thromboembolism), but without sufficient proof (Hamilton, 1966a). Although Ae. abstrusus is very specific in the tissue sections, differential pathological diagnosis must exclude the presence of ascaride and strongyloides larvae in the lungs. On the other hand, the parasite Dirofilaria immitis causes similar clinical signs (respiratory distress, abnormal radiographic pulmonary opacities, and increased eosinophil counts) (Calvert and Mandell, 1982). Differential clinical diagnosis is very important because treatment and prognosis are very much different.

References

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Received: 5 October 1999
Accepted: 16 October 1999

GRABAREVIC, Z., S. CURIC, A. TUSTONJA, B. ARTUKOVIC, Z. ŠIMEC, K. RAMADAN, T. ZIVICNJAK: Ucestalost i prostorno pojavljivanje plucnog nametnika Aelurostrongylus abstrusus u macaka u Hrvatskoj. Vet. arhiv 69, 279-287, 1999.

SAZETAK

Plucni nametnik macaka Aelurostrongylus abstrusus ima neizravan zivotni ciklus u plucima macaka. Najcešce se nalazi u terminalnim bronhiolima i alveolama. U radu su istrazivane dvije populacije macaka. Prvu skupinu su cinile macke lutalice (N=50) iz neurbaniziranih djelova Hrvatskog zagorja, a druga je obuhvacala macke iz zagrebackog podrucja. Za drugu skupinu macaka podaci su dobijeni koprološkim pretragama (N=529) obavljenim u Zavodu za Parazitologiju i analizom makroskopskih i patološkohistoloških nalaza razudenih macaka (N=128) u Zavodu za opcu patologiju i patološku morfologiju Veterinarskog fakulteta u Zagrebu u razdoblju od osam godina (1990.-1998.). U prvoj skupini macaka utvrdena je aelurostrongiloza u 22% (11 macaka) pregledanih zivotinja. Koprološkom pretragom ova parazitoza je utvrdena samo u 0,38% slucajeva, dok je histopatološka pretraga dokazala ovu bolest u 3,9% slucajeva. Histološki, utvrdene su alveole i bronhioli ispunjeni s jajašcima i larvama parazita Aelurostrongylus abstrusus, pucanje alveolarnih septi, stanicni infiltrat (vecinom eozinofili, makrofagi, limfociti i poneka divovska stanica), peribronhijalna stanicna infiltracija te upecatljiva hiperplazija i hipertrofija glatkog mišicja plucnih arterija.

Kljucne rijeci: macke, plucni nametnik, Aelurostrongylus abstrusus, ucestalost, Hrvatska