Understanding Lungworm in Cats: Symptoms and Treatment
1. Introduction
The objective of this project is to create in-depth overviews within this research center that will provide veterinarians with the practical and current knowledge required to understand, diagnose, treat, and prevent lungworm infections in cats. These overviews will focus on clinical information, i.e., signs of illness in infected cats, diagnosis, treatment options, and information important for concerned pet owners. Other resources for veterinarians, regulators, epidemiology researchers, and academicians, which will be housed on the website in the future, are detailed in the methodology section.
Lungworms are parasitic nematodes that easily gain the attention of pet owners and veterinarians due to their potential to affect cat respiratory health. Pet owners are not only concerned but also suspect that their cats are at risk for this infection, questioning the effectiveness of toxin products or their own risk for the infection. Importantly, the perceived threat of lungworms among veterinarians appears to be growing. Further, some FIV+ cats on long-term corticosteroids were deemed naturally infected with A. chabaudi and A. abstrusus. Pet-owning cat owners in Canada have common misconceptions about lungworms, and only half have heard of lungworms. The overall goal of this project is to create a resource that will educate and inform veterinarians about recognized lungworm species in Canada. As this project evolves and lungworm research in Canada and worldwide advances, updates to the overview will be made. In addition to providing a detailed overview of lungworms in cats, we provide an alternative treatment to fenbendazole for a given lungworm here.
Given the geography of the research and the funding agency providing treatment and prevention resources, a survey of veterinarians in Canada revealed that about half of the respondents suggest that cats likely have a high probability of getting ill from lungworms. A lack of owner recognition of lungworm and many other parasite species of interest is common in many parts of the world. Awareness of the scientific names of lungworms may even be uncommon, so infected cats that are tentatively or presumptively diagnosed are often reported as 'cat lungworm' positive. The goals of this overview are to discuss the clinical signs associated with lungworm infection, methods of diagnosis, options to treat infection, and potential infection prevention.
2. Causes and Transmission of Lungworm in Cats
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There are several terrestrial and aquatic snails that can become infected with these larvae in the natural environment, but A. abstrusus is mostly seen in slugs, and R. philomycus is transmitted by the slug Hemphillia. Adult Aelurostrongylus lay eggs in the lung of the cat, which hatch within a few days. The newly hatched larvae are coughed up by the cat and swallowed, eventually being passed out into the environment in the cat’s feces. The cats then become infected by eating snails or slugs that have the larvae inside them. Once ingested by the cat, the larvae make their way from the stomach into the cat’s lung, where they develop into adult lungworms. The adult worms produce eggs, and once these hatch, the small larvae are coughed up by the cat and swallowed, to be passed out in the feces to start the life cycle again. Although lungworm infection primarily affects cats who live outdoor lives, cats who live exclusively indoors can also become infected. Snails and slugs are commonly found in outbuildings such as garages and sheds, and it is possible that cats could become infected by eating snails or slugs that are brought into the house unintentionally.
3. Symptoms of Lungworm Infection in Cats
Lungworm infection affects cats in various ways, and this depends on the location of lungworm within the airways and also the response of the cat’s immune system. Changes that may indicate there is something wrong in the respiratory system or that the cat is unwell are referred to by vets as "clinical signs." Remember that in many cases, cats will not show any of these symptoms. These can be divided into respiratory symptoms and general symptoms, although not all cats will show unspecific symptoms such as weight loss or secondary infections. Most of the respiratory symptoms are due to the presence of larvae in small airways, while most symptoms in cats infected are usually related to problems in the large airways.
Some cats, especially when the infestation is recent, can show subtle symptoms, such as an increase in respiratory rate. They may cough, show general inactivity, or become what is often referred to as lethargy. As the illness progresses, no matter which lungworm species are involved, further coughing, gagging, retching, or even vomiting may be observed. The cough may be present all the time or mainly after physical activity or excitement. Sometimes the breathing can be noisy and labored: the cat may present with shortness of breath or even open-mouth breathing and might perform what is called "abdominal tagging," which is when the cat uses its abdominal muscles to help its breathing, but the effort is visible from outside. One species is the one that more often causes cough and severe upper respiratory signs, while another is associated with less severe and acute signs. Some of the signs of illness do not originate only in the respiratory tract; indeed, heavy infestations can drain large quantities of blood and nutrients away from the rest of the body. These are general symptoms such as poor condition, weight loss, inappetence, and diarrhea. As morbidity and a number of worms decrease, these symptoms may resolve. However, a praiseworthy improvement after a period of apparent mildness may be due to susceptibility to secondary infections such as bronchitis or bacterial pneumonia. Therefore, even if a cat's symptoms disappear, contact a veterinarian to investigate the origin and treat these symptoms. Cough is a very useful function in respiratory disease; it supports the cleansing and support of the airways in healthy animals and is heightened in animals affected by certain respiratory diseases. However, contact your veterinarian immediately if your cat shows any signs of chronic cough. It is always worth visiting your veterinarian if your cat has a breathing disorder.
4. Diagnosis and Testing for Lungworm in Cats
Because the clinical signs associated with lungworm infection can mimic many other diseases, owners are encouraged to touch base with their veterinarian at the appearance of the first concerning signs. Clinical suspicions should consider the history of potential exposure, parasitic and otherwise, including travel or exposures in uncontrolled or free-roaming cat populations. A thorough veterinary examination that includes a complete history and clinical pathology examination can rule out systemic diseases and underlying illness. A fecal examination is the gold standard for the diagnosis of most intestinal parasitism. A negative fecal test does not completely rule out lungworm infection. Though fecal testing can be helpful in examining for lungworm inclusion, specific tests that look for lungworm larvae are preferred methods for parasite identification.
Several diagnostic tools can be used to diagnose lungworm infection in cats. Fecal testing may identify larvae, eggs, and/or adult worms, giving a specific diagnosis. However, possibilities to misdiagnose are present. Imaging studies can show the lungworm inside the airways, helping to eliminate any other possibilities of differential diagnosis. Bronchoscopy might record the existence of an adult lungworm or the presence of eggs associated with worm specimens found in the upper respiratory tract. Cytology might show a different number of cells in the airway canal, ruling out the diagnosis of other possibilities of differential diagnosis. No single test is 100% accurate for lungworm infection in cats in part due to the challenges in detecting the parasite and because clinical signs may be non-specific or subtle. Several tests might be necessary to confirm the diagnosis and to rule out other differential diagnoses. Making a diagnosis enables us to proceed appropriately with treatment.
5. Treatment Options for Lungworm in Cats
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Because cats become dehydrated when they do not eat, eat too little, or vomit, and lungworm typically makes them do these things, any treatment program tailored to the individual cat must focus on maintaining a balance between effective deworming and supportive care. Subcutaneous fluids at home are often required to support cats feeling ill from lungworm, but those who cannot be coaxed to use the litter box may warrant hospitalization for intravenous fluids, diagnostic evaluation, and critical care. Left untreated, lungworm occasionally takes cats' lives, primarily through debilitation, malnutrition, and dehydration. Common treatment side effects include transiently worsened coughing and diarrhea. Once medications are finished, a follow-up fecal evaluation at the end of the recommended course of treatment to assure cure before ceasing regular deworming is the veterinarian's preferred next step in monitoring resolution of lungworm disease. Keeping indoor cats indoors and worming outdoor cats regularly is the best way to prevent them from getting new lungworm infections.