Lungworms are parasitic worms that primarily inhabit the respiratory system of various animals. They affect a range of hosts, including domestic pets like dogs and cats, and livestock such as cattle, sheep, and pigs. While most are found in the lungs, some species can also reside in associated areas like pulmonary arteries. Understanding their appearance is important for identifying their presence and managing animal health.
Adult Lungworms: What They Look Like
Adult lungworms are macroscopic, meaning they are visible without a microscope. They appear as slender, thread-like worms, typically translucent white to pale cream or yellowish. Their size varies considerably by species. For instance, Dictyocaulus viviparus in cattle can be 3.5 to 8 centimeters long. Metastrongylus in pigs are 2 to 5 centimeters, with females often longer than males. Muellerius capillaris in sheep and goats are fine, thin, and often coiled within lung tissue. These worms possess a flexible, tough outer cuticle. Some species, like Angiostrongylus vasorum (French heartworm), have a distinct barber-pole appearance in females due to spiraling ovaries. Their elongated body shape allows them to navigate the host’s respiratory system.
Microscopic Stages: Larvae and Eggs
Unlike adults, lungworm larvae and eggs are microscopic. These forms are crucial for diagnosis. Many species, such as Dictyocaulus viviparus, release eggs that quickly hatch into first-stage larvae within the host’s airways. These larvae are often motile. For example, Dictyocaulus viviparus first-stage larvae are 400 to 450 micrometers long, with a granular intestine and a bluntly pointed tail. Other larvae, like Aelurostrongylus abstrusus in cats or Angiostrongylus vasorum in dogs, have specific morphological features, such as a kinked tail, which aids identification. Some species, like Metastrongylus, produce eggs that are already larvated when passed in feces. These eggs are typically oval, thick-shelled, and contain a developing larva, measuring about 40 by 50 micrometers. Their presence in samples like feces is key for diagnostic purposes.
Where Lungworms Are Found in the Host
Lungworms primarily inhabit the respiratory system. Adult worms are typically found in the bronchi and bronchioles, the air passages within the lungs. For instance, Dictyocaulus viviparus adults reside in the trachea and bronchi of cattle. Other species, such as Metastrongylus, are also found in these air passages. Some lungworm species exhibit variations in their preferred location. Muellerius capillaris is found deeply embedded within lung tissues, often associated with small gray spots or nodules. Angiostrongylus vasorum (French heartworm) lives in the pulmonary arteries and the right side of the heart. Larval stages are often passed in the feces, making them detectable.
How Lungworms are Identified
Identifying lungworms typically involves microscopic examination of samples collected from the infected animal. Adult worms are rarely seen directly, except during post-mortem examinations or specific medical procedures like bronchoscopy, due to their deep location within the respiratory system. During necropsy, tangled clumps of white worms may be visible in the larger air passages of the lungs. The most common method for diagnosing lungworm infection in live animals is through the microscopic examination of fecal samples, because many lungworm species shed larvae or larvated eggs in the animal’s feces. A specialized technique, the Baermann technique, is frequently used to isolate and detect these larvae from fecal matter, as it allows motile larvae to migrate out of the sample into a collection fluid. Samples obtained directly from the respiratory tract, such as tracheal washes or bronchoalveolar lavage (BAL) fluids, may also be examined for the presence of larvae, eggs, or inflammatory cells. While chest X-rays can reveal abnormalities in the lungs consistent with lungworm infection, they are not specific for diagnosis and are often used in conjunction with fecal tests or other methods. Larvae or eggs may be shed intermittently, so multiple fecal samples collected over several days can increase the chance of detection.