Parasitic infections of the lower respiratory tract Flashcards
What is the epidemiological cycle for Aelurostrongylus abstrusus
Aelurostrongylus abstrusus has an indirect life cycle and cats are the definitive host
Adult A. abstrusus lungworms live in the respiratory bronchioles and alveolar ducts of cats
- after mating, the females produce eggs that hatch in this same location
The first stage larvae ascend the bronchial tree to the pharynx, where they are swallowed and excreted in the feces and into the environment
- L1 are then ingested by gastropods that act as intermediate hosts with rodents, lizards, snakes or birds acting as paratenic hosts
Cats become infected by ingesting a gastropod and/or a paratenic host
- if a cat ingest the paratenic host, the L3 larvae will penetrate the GI tract and migrate through the peritoneal and thoracic cavities to the lung where they will develop into adults and start producing eggs after 4-6 weeks
The prepatent period is 35 to 48 days
The peak of L1 excretion in feces occurs around 10 to 14 weeks postinfection and lasts for months
What are the limitations of the Baermann technique to investigate A. abstrusus infection
The Baermann technique is considered the most sensitive method for larval detection but sensitivity is less than 90%
It cannot detect prepatent infection and larvae are shed intermittently, even in cats with clinical signs
Explain why A. abstrusus infection is an important differential for feline bronchial disease
Signs of infection can mimic other LRT diseases (e.g., dyspnea, open-mouthed abdominal breathing, coughing, wheezing, …)
Radiographs of affected cats often demonstrate a bronchointerstitial pattern
BAL fluid cytology may be eosinophilic, lymphocytic, neutrophilic or mixed
Affected cats can show an initial positive response to administration of corticosteroids and bronchodilators
What is the heartworm life cycle in cats
HWD is caused by the filaroid nematode Dirofilaria immitis, which is transmitted by mosquitos and for which dogs are the usual definitive host
The sexually dimorphic adult heartworms mate within an infected dog’s pulmonary artery, producing immatures forms called microfilariae
- circulating microfilariae are ingested by mosquitoes feeding on infected dogs
Within mosquitoes, microfilariae transform into larval stages
- transformation of stages L1 to L3 occur within the mosquito, and L3 is the form that is transmitted from mosqitos to dogs and cats
Maturation from L3 to other larval stages occurs in subcutaneous tissues and peripheral veins of mammalian hosts
- immature worms in peripheral veins are carried in the bloodstream to and through the heart, with adult heartworms ultimately residing in the caudal pulmonary arteries
What is suggested by the loxer prevalence of HWD in cats compared to dogs
The lower prevalence in cats suggests the cat is an imperfect host for the parasite likely due to immune-mediated clearance of microfilariae
What are the clinical signs and physical examination findings in cats with HWD
Clinical signs can vary from inapparent or mild to acute or chronic respiratory tract signs
- sudden death is reported
Clinical signs are associated with two stages of disease
- first, arrival of heartworms in the pulmonary vasculature
- later, death of adult heartworms
Arrival of immature worms in the pulmonary arteries and arterioles is associated with an acute vascular and parenchymal inflammatory response and the death of most of the immature heartworms
- clinical signs in this stage are often mistaken for asthma or bronchitis, but are actually HARD
Death of adult heartworms results in pulmonary inflammation and thromboembolism that can lead to acute lung injury
What are the primary reasons for heartworm testing in cats
To establish a diagnosis in cats that are suspected of infection
To monitor the clinical course of cats diagnosed with HWD
To establish a baseline reference prior starting prophylaxis
Why testing for microfilaremia is not recommended in cats
Cats are rarely microfilaremic, so tests for microfilaria are not recommended
What are the limitations of antigen testing in cats suspected of HWD
Heartworm antigen testing detects mature female heartworms and is considered the gold standard in dogs
- because cats may have unisex infections with only male worms and symptomatic immature infections are common in cats, none of the available antigen tests can be relied upon
- false-negative antigen results are associated with mild infections, immature female worms, unisex male infections, and/or problems with the test
