Identifying Internal Parasites in Cattle

Strongyle Parasites

Trichostrongyle (“Strongyle”) Parasites are a group of nematodes whose egg are morphologically indistinguishable under a microscope (i.e. their eggs all look the same) and cannot be differentiated based solely on their eggs; there is too much variation from genus to genus, species to species, female to female. The following parasites are considered ‘strongyles’.

Cooperia spp. (The Cooperiads)

The Cooperiads have become one of the most important worms in cattle due to their resistance to nearly all dewormer classes, particularly the Macrocyclic Lactones (Avermectins/Milbemycin), and their seeming omnipresence in our animals. These nematodes are found in the small intestines of cattle and are blood eating parasites. Though this group is one of the top contenders of concern in young animals, the parasites are only mildly pathogenic, and generally do not cause a lot of physical harm to their hosts. However, heavy, persistent infections can surely shave off dollars at the time of sale, as worm burdens can lead to significant decreases in average daily gains.

Ostertagia ostertagi (Brown Stomach Worm)

The Brown Stomach Worm is one of the most important cattle worms (likely THE most important) in the USA/temperate climates. It lives in the abomasum and undergoes a pronounced histotropic (“tissue/cyst forming”), hypobiotic (“arrested development”, akin to hibernation) form at the 4th life cycle stage. This occurs in the winter in the Northern USA and in the summer in the Southern USA (it is a little bit of both in the Western USA). The larvae are encysted in the abomasum wall during the time of the year that the weather is most adverse for survival on pasture; this is called Pre-Type 2 Ostertagiasis. When the weather is favorable for survival, the larvae exit their cysts (nodules) en masse, creating wounds that require protein for repair; this is called Type 2 Ostertagiasis. After exiting the abomasum wall, the larvae resume the normal life cycle, cycling on pasture and infecting cattle during the favorable seasons that are conducive for survival; this is called Type 1 Ostertagiasis. The most pathogenically significant type of Ostertagiasis is Type 2. Heavy infections of Ostertagia can lead to chronic diarrhea, weight loss, and a malfunctioning abomasum (due to the encysted larvae and their subsequent exit). Ostertagia causes significant pathology in all ages of cattle.

Haemonchus placei (Barber Pole Worm)

The Barber Pole Worm is found in the abomasum of cattle and is a blood eating parasite. Generally speaking, the BPW in cattle is of far less concern when compared to its relative in small ruminants. Though it can become an issue in high numbers in cattle, it very rarely leads to the level of anemia and death that is present in small ruminants and camelids. The cattle BPW has shown resistance to all classes of dewormers, though to a much lesser extent than the small ruminant BPW.

Trichostrongylus axei (Bankrupt Worm)

The Bankrupt Worm is a nematode that is found in the small intestines of cattle. Though the name elicits an image of a pathogenic worm, the Bankrupt Worm does not take a lot from the host animal and does not produce very many eggs per day (>100/day/female worm). This worm is typically susceptible to most dewormer classes, though it is not recommended to use dewormer to control this worm (due to its unimportant nature).

Oesophagostomum radiatum (Nodular Worm)

The Nodular Worm is found in the intestinal lining of the end of the small intestine and beginning of the large intestine of ruminants. It invades the intestinal lining as a natural part of the life cycle and can cause significant pathology in animals when found in high numbers. The parasite is typically found in low numbers on roughly 30-50% of operations and generally does not cause a problem. However, due to penetrating the skin as an infection route, if your operation has consistently wet conditions (i.e., heavy and constant rain, dairy operations, etc.), this worm might become an issue. The success of this parasite generally requires a “chronic carrier” host; this is a host animal that will always harbor a heavy infection and persistently seed the pastures with Oesophagostomum eggs.

Other internal parasites

Other internal parasites that infect cattle that can be important in certain situations (i.e. found in high numbers, immunocompromised animals, etc.) Those with unique eggs are:

Nematodirus spp. (Intestinal Thread-Necked Worm)

The Intestinal Thread-necked Worm is a large worm that is found in the small intestines of ruminants and is found in roughly 10-30% of operations. This parasite can cause significant pathology due to it strangling the intestinal villi, which are very important to the digestion process, as a means to stay in place. This action, called Thigmokinesis, causes the host to reject the villus from the intestinal lining and can cause significant damage. This can lead to weight loss/skinny animals and profuse diarrhea/dehydration. There is no treatment threshold for Nematodirus; if a single egg is seen during a fecal egg count, a Benzimidazole dewormer should be administered. There is an exposure-induced immunity with this worm, limiting infections to younger stock (generally).

Toxocara vitulorum (Cattle Ascarid/Roundworm)

The Roundworm of cattle is most significant in calves under 6 months of age, with calves under 3 months old most severely affected. There is generally an acquired age immunity with this worm, unless an older animal was not infected at a young age. The larvae of this worm can be passed from mother to offspring via milk (Transmammary Infection) and infections can be measured in calves as young as 3 weeks old. Heavy infections can lead to diarrhea, weight loss and death. It is found in tropical/subtropical regions.

Trichuris spp. (Ruminant Whipworm)

The Ruminant Whipworm is an internal parasite that is found in the large intestine of ruminants and eats blood. This worm threads 2/3 of its body into the intestinal lining and is very anchored in place, making it difficult to kill with dewormers. The female parasites do not release eggs at a steady interval, instead coordinating the population’s egg output every few days. This coordinated egg dumping makes it difficult to accurately detect if only a single fecal egg count is performed; an egg count must be performed every day for 3-5 days in order to confirm infections. It is typically found in low numbers on roughly 10-25% of operations and generally does not cause significant pathology. The Ruminant Whipworm is typically disregarded and tolerated due to the general failure of dewormers and difficulty to detect via fecal egg counts.

Bunostomum phlebotomum (Cattle Hookworm)

The Hookworm of cattle is a parasite that lives in the small intestines and eats blood. Due to its infection route (skin penetration), it requires ample moisture to perpetuate its life cycle (wet/moist geographic regions, dairies, dirty concrete pens that do not dry out, etc.). These skin penetrating larvae enter the blood stream and break out into the lungs, are coughed up and the swallowed into the gastrointestinal tract (called ‘tracheal migration’). Heavy infections can lead to anemia, intermittent diarrhea, and rapid weight loss; low to moderate infections are generally nonpathogenic.

Strongyloides papillosus (Intestinal Threadworm)

The Intestinal Threadworm is found in the small intestine of ruminants and can be found on the majority of operations; this nematode typically does not cause significant pathology. Due to the complexity of its life cycle, its nearly permanent presence in the environment, and the fact that there is no good treatment for it, this parasite is generally disregarded and tolerated.

Moniezia benedeni (Common Cattle Tapeworm)

The sheep tapeworm is found in the small intestines of cattle and is of very little concern. Deworming treatment for tapeworms in cattle is not generally advised, as they do not cause significant pathology, and treatment is not usually required.

Eimeria spp. (Coccidiosis)

Coccidiosis is a protozoon parasite that is found in the small intestines and typically causes significant pathology in young and immunocompromised animals. Small to moderate amounts of cocci oocysts can be found in nearly all fecal samples but should only be treated if the infections are extremely high. Generally, coccidiosis is only a problem in birthing or winter barns where young animals are housed on soiled bedding. Coccidiosis is a ‘self-limiting’ disease, meaning if you remove an infected animal from the contaminated environment and get them on a good plane of nutrition, they will clear the infection without treatment in about 7-10 days. If the animal needs to be treated, amprolium or a sulfa drug is sufficient. There are cocci preventatives that can be added to the feed, as well.

IDENTIFYING INTERNAL PARASITES IN CATTLE