Introduction
As a pet science blog author, I’ve always been fascinated by the complex world of parasites. Today, I’m diving into the intriguing world of Strongyloides, a group of parasites that can infect not only our beloved pets but also humans. Let’s explore the fascinating life cycle, symptoms, diagnosis, treatment, and control methods for these thread-like worms.
The Threadworm: A Closer Look
Strongyloides are a unique group of parasites that can infect a variety of hosts, including carnivores and humans. The feline intestinal threadworm, Strongyloides tumefaciens, and S. stercoralis, which can infect dogs and cats, are of particular interest. Interestingly, each host species appears to be infected by a different strain or variety of the parasite.
These thread-like worms are quite unique, with a parasitic form and a ‘free-living’ form that can thrive outside a host. Another fascinating fact is that only female parasitic worms exist, with no adult males in sight.
Life Cycle of the Intestinal Threadworm
Strongyloides species can infect a wide range of animals, from horses and pigs to reptiles and wild animals in Africa. The life cycle of these worms is quite extraordinary.
The female worm resides in the host’s intestine, laying eggs that can develop without fertilization. The eggs hatch into larvae in the intestine and are excreted in feces. These larvae can develop into either infective parasitic larvae or free-living worms of either sex.
The parasitic larvae enter a new host by penetrating the skin, migrating to the lungs, traveling up the trachea, and being swallowed. The free-living larvae mate but only produce infective larvae that must enter a host to survive.
Factors Affecting Larval Development
The development of larvae into parasitic or free-living forms is influenced by several factors, including the severity and length of infection, the species and age of the host, and the host’s immune system status.
In some cases, migrating larvae can remain in a dog’s tissues, and in female dogs, they can even reach the mammary glands, leading to direct transmission to puppies through milk. This is one reason why puppies can develop severe infections at a young age.
Disease Caused by Intestinal Threadworms
In dogs, most infections are either inapparent or cause only mild diarrhea. However, in young puppies, infections can become severe and even fatal. This is particularly important in pet stores and kennels.
In severe infections, dogs may exhibit symptoms such as diarrhea, loss of appetite, weight loss, weakness, and dehydration. Younger animals are more susceptible, and infections are more common during the summer months due to high temperatures and humidity.
In cats, S. tumefaciens generally does not cause disease, but in some cases, small white nodules can develop in the colon, leading to chronic diarrhea.
Signs and Symptoms in Humans
In humans, Strongyloides infestations can cause skin inflammation at the site of larval entry, cough, or respiratory difficulties as the larvae migrate through the lungs.
The intestinal illness caused by Strongyloides infections can range from mild to fatal. Most cases are asymptomatic, but in individuals with compromised immune systems, severe illness can occur. Symptoms can include abdominal pain, diarrhea, nausea, vomiting, weight loss, weakness, and sometimes constipation.
In some cases, larvae that hatch from eggs in the intestine may stay and develop into adults, leading to a significant increase in the number of worms and the severity of disease. Autoinfection, where a person is the source of their continued infection, can occur, and some individuals have been known to remain infected for up to 35 years.
Diagnosis of Intestinal Threadworm Infestations
Diagnosis can be made by identifying eggs or, more commonly, larvae in fecal samples through microscopic examination. The Baermann technique, a special procedure, can be used to concentrate larvae in a stool sample, making them easier to find.
Treatment of Intestinal Threadworm Infections
Until recently, thiabendazole was the most common drug used to treat Strongyloides infections, although it is not FDA approved for cats. Fenbendazole and ivermectin are now recommended treatments, but they are also not FDA approved.
It has been suggested that ivermectin could be given at an oral dose of 0.8 mg/kg (four times the usual dose), and this treatment may need to be repeated. However, these medications are not very effective in eliminating larvae that may be encysted in the tissues.
Control Methods for Strongyloides
Strongyloides larvae are killed by cold temperatures and in dry environments. Keeping animals in dry, clean environments and maintaining good hygiene are essential control measures.
In breeding facilities, controlling and eliminating Strongyloides can be challenging,