The expanding universe of three parasites - Veterinary Medicine
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The expanding universe of three parasites
Three parasites that primarily affect dogs are becoming an increasing concern in the United States. Are these three emerging parasites on your radar?


VETERINARY MEDICINE


Signalment

In Europe, there does not appear to be any sex or breed disposition, although one study did show Cavalier King Charles spaniels and Staffordshire bull terriers were overrepresented among dogs with canine pulmonary angiostrongylosis compared with the control group.3,8 In contrast, most dogs with canine pulmonary angiostrongylosis in Newfoundland are beagles used for rabbit hunting.1

Canine pulmonary angiostrongylosis has been reported in dogs as young as 3 months old and as old as 14 years; however, more than half the European cases have been reported in dogs ≤ 1 year, whereas the median age in Newfoundland cases is 4.25 years.1,2

Clinical findings

Clinically, infected dogs may be asymptomatic or minimally affected or have severe disease. Classic canine pulmonary angiostrongylosis usually presents with respiratory signs, including dyspnea and coughing.1,2,4,6,8 Crackles may be present in severe cases. Dogs with chronic infections can have pulmonary hypertension, cor pulmonale, and subsequent systolic heart murmur. Other signs may include depression, exercise intolerance, anorexia, weight loss, vomiting, or diarrhea. Severe coagulation disorders have also been identified in chronically infected dogs.1,2,9 Petechial and ecchymotic hemorrhages, hematomas (both traumatic and surgically induced), epistaxis, hemoptysis, intracranial hemorrhages, hematuria, and gastrointestinal bleeding have all been reported.1,2,9 Thrombocytopenia, prolonged activated partial thromboplastin and prothrombin times, the presence of fibrin degradation products, hyperglobulinemia, anemia, or Factor V deficiency are associated with these cases.1,2,9 Thus, a consumptive coagulopathy is indicated, but the mechanisms involved are not defined.

Diagnosis

Because the clinical spectrum of canine pulmonary angiostrongylosis is not unique, many differential diagnoses are usually considered, including viral respiratory disease, immune-mediated thrombocytopenia, and other cardiopulmonary parasites. Thus, an initial work-up, based on the severity of signs, has been described.2


3. First-stage larva of Angiostrongylus vasorum, stained with Lugol’s iodine. Note the kinked-tail at the posterior end with the short, dorsal spine (arrow). This characteristic will differentiate first-stage larvae of A. vasorum from those of Crenosoma vulpis and Strongyloides stercoralis (40X). (Photo courtesy of Dr. Gary Conboy, University of Prince Edward Island.)
Parasitologic diagnosis depends on finding L1 (Figure 3) in the feces by using the Baermann techinque.1,2 Because of the sporadic shedding of larvae in the feces, it is recommended that samples be collected on three consecutive days to enhance detection. The L1 can also be found in direct fecal smears, particularly if clinical signs are moderate to severe or recovered by tracheal wash or bronchoalveolar lavage. Angiostrongylus vasorum L1 are 310 to 399 m in length with an anterior cephalic button and an S-shaped tail (severe kink) with a dorsal spine. These features distinguish A. vasorum L1 from those of other canine parasites, such as Crenosoma vulpis or Strongyloides stercoralis.

Treatment

Several anthelmintics and therapeutic regimens have been used to treat canine pulmonary angiostrongylosis. Recommendations include milbemycin oxime (0.5 mg/kg once a week for four weeks), topical moxidectin (2.5 mg/kg; imidacloprid-moxidectin spot-on combination product applied once), or fenbendazole (20 to 50 mg/kg daily for five to 21 days).1

Not every treatment is 100% efficacious; thus, follow-up fecal examinations should be conducted three to seven days after completion of the treatment regimen. An additional three-day Baermann test should be conducted again at three months and then twice a year. If no larvae are found, then further testing is performed if suspicious clinical signs recur.2 Resolution of clinical disease but not infection can occur; in these cases, retreatment is necessary.

Post-treatment complications may occur, such as severe dyspnea or ascites. Strict cage rest for the initial two or three days of treatment is recommended. The use of additional supportive therapy, such as antibiotics, immunosuppressive doses of corticosteroids, and bronchodilators, will depend on the clinical presentation.2

Prevention

In endemic and hyperendemic areas, monthly anthelmintic prophylaxis may be considered. Although adult nematodes were not found after topical moxidectin was administered at four days or 32 days postinfection,1 protocols for its, or any other anthelmintic's use, have not been established or verified. Removing feces will be a tremendous help, as it will break the life cycle and reduce environmental contamination. Owner education regarding the means by which dogs become infected and how off-leash walking of dogs contributes to their risk is advised.2 Finally, monitoring by using Baermann tests should be incorporated into the yearly wellness examination to help identify infected but asymptomatic animals.


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Source: VETERINARY MEDICINE,
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