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Baermann test: Strongyloides stercoralis, first stage larva, iodine stained.
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Figure 5: Baermann test: Strongyloides stercoralis, first stage larva, iodine stained.

Mentions: The accurate and definitive diagnosis of lungworm infections is achieved by the identification of parasitic biological stage(s) in a series of samples. For nematodes whose eggs hatch in the bronchial tree of the infected animals, i.e. A. vasorum, C. vulpis and A. abstrusus, L1 s are the "target" to be identified in the faeces by using copromicroscopic techniques such as direct smears, faecal flotation and Baermann examinations. Direct smears are inexpensive and easy to perform but have poor sensitivity due inadequate sample size and will only detect infections in animals that are shedding large numbers of larvae in the faeces [21,126]. Faecal flotation examinations also lack detection sensitivity due to issues of sample size and the damaging effects of the flotation media on the larvae (Figure 3). In fact, high specific gravity concentrated salt or sugar solutions tend to induce larval osmotic damage due to dehydration. Larvae may be completely damaged and therefore undetectable or suffer a loss of morphologic detail rendering accurate larval identification difficult to impossible, especially for inexperienced diagnosticians [21]. Zinc sulphate (specific gravity = 1.18 - 1.2) appears to be the most reliable media for use in the detection of L1 s on fecal flotation but still may miss 40-90% of the positive animals [127]. The Baermann faecal examination method remains the gold standard for the diagnosis of the infections caused by A. vasorum, C. vulpis and A. abstrusus, due to the positive hydro-/thermo-tropism exhibited by live L1 [21,93]. When the larvae are present in the stool samples, a thorough morphometric and morphological examination is required for an accurate identification of L1. Lungworm larvae should be differentiated from i) each other, ii) those of other less common parasites, iii) hookworm larvae that may be present in samples that have been allowed to incubate and iv) free-living or plant parasitic nematodes that may be present in samples collected from the ground. In addition to A. abstrusus (Figure 4), another less common parasitic larvae that may be detected using the Baermann technique in feline fecal samples includes the lungworm Oslerus rostratus. In canine samples, larvae of the lungworms Filaroides spp. and Oslerus osleri as well as those of the intestinal parasite Strongyloides stercoralis (Figure 5) may also be detected and need to be differentiated from A. vasorum (Figure 6) and C. vulpis (Figure 7) [93]. The finding of L1 s of Filaroides spp. and Oslerus spp. in samples examined using the Baermann method is unlikely because larvae of these nematodes are lethargic and therefore do not migrate out of the faeces. Although false negative results commonly occur, detection of these larvae in faeces is more reliably accomplished through centrifugal faecal flotation using zinc sulfate solution (specific gravity = 1.2) than with the Baermann technique. Table 3 details the key morphometric and morphological characters (i.e. length, width, esophageal and tail morphology) to be evaluated when nematode larvae are found in canine or feline faeces. The presence of nematode contaminants in the faeces greatly complicates the evaluation of the sample. Due to the large number of species of free-living/plant parasitic nematodes involved, there is no single morphological character that allows the diagnostician to differentiate the contaminants from the parasitic L1. A diagnostician should suspect the possibility of contaminants if the sample contains adult stages (i.e. males with spicules, females with vaginal opening and uterus containing eggs) or the size measurements of the nematodes recovered are inconsistent with the range expected for parasitic L1 (i.e. 150 - 412 microns). Since S. stercoralis may develop a free-living generation if the faecal sample is allowed to incubate, even the presence of adult stages does not definitively indicate contamination has occurred. When contamination has been suspected, specific instructions should be given to the animal's owner on proper sample collection (faeces should be collected immediately after deposit on the ground) and the animal should be re-tested.

Canine and feline cardiopulmonary parasitic nematodes in Europe: emerging and underestimated

Traversa D, Di Cesare A, Conboy G - Parasit Vectors (2010)

Bottom Line: Capillaria aerophila).The reasons of this emergence are little known but many drivers such as global warming, changes in vector epidemiology and movements in animal populations, may be taken into account.In particular recent advances in epidemiology, clinical and control are described and discussed.

Affiliation: Department of Comparative Biomedical Sciences, University of Teramo, Teramo, Italy.

Cardiopulmonary nematodes of dogs and cats cause parasitic diseases of central relevance in current veterinary practice. In the recent past the distribution of canine and feline heartworms and lungworms has increased in various geographical areas, including Europe. This is true especially for the metastrongyloids Aelurostrongylus abstrusus, Angiostrongylus vasorum and Crenosoma vulpis, the filarioid Dirofilaria immitis and the trichuroid Eucoleus aerophilus (syn. Capillaria aerophila). The reasons of this emergence are little known but many drivers such as global warming, changes in vector epidemiology and movements in animal populations, may be taken into account. The purpose of this article is to review the knowledge of the most important heartworm and lungworm infections of dogs and cats in Europe. In particular recent advances in epidemiology, clinical and control are described and discussed.

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