The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) has a rich history. Over the 50 plus years we have existed, TVMDL professionals have worked tirelessly to provide the most accurate and up to date resources to our clients. The following excerpt is part of an ongoing series of articles written by TVMDL’s first director, Dr. William Sippel, and other professionals from the earlier days of TVMDL. Some articles were written for features in The Cattleman publication where others were case studies over recent diagnoses. We hope you enjoy this look back on TVMDL’s history.
Veterinary Outlook: Lungworms
By William L. Sippel, V.M.D.
Lungworm infestation of cattle can be a very serious problem resulting in the death or stunting of young animals. While cattle 4 to 10 months of age are most often affected, adults can also acquire lungworm infestation.
The symptoms produced in affected cattle are those of pneumonia of emphysema. The severity of the symptoms is directly related to the number of infective larvae ingested. If the number is large, a very severe disease is produced marked by sudden onset and rapid, shallow, open-mouthed breathing. There is often a sort, frequent cough accompanied by a nasal discharge and temperature around 105°F. Animals that are lying down will usually start coughing when they rise. It is not unusual for cattle with lungworms to also have other types of intestinal parasites that produce anemia and marked loss of weight. Diarrhea is frequently observed and is important in spread of the parasite larva on the pasture. Affected animals do not lose their appetite until later in the course of the disease which may be short, as 75 percent to 80 percent of acutely affected animals may die in 3 to 10 days. Infested animals must be handled with care so as not to overtax the minimal amount of breathing capacity the lungs have remaining. If excited or driven, they may collapse and die of suffocation.
Animals that have consumed a smaller number of infective larvae will be less severely affected. They present roughly the same type of symptoms but they are less severe. These animals often have a grunt when they exhale. Coughing, rapid breathing, etc. are similar to acute cases. Subacutely affected animals lose weight rapidly and may be stunted but few die.
The life cycle of this parasite is direct in that the adult parasites in the lungs pass eggs that hatch very quickly and living larvae are passed in the manure. These fall the ground with the manure and the larvae migrate only a very short distance. For this reason in order to spread, the manure needs to be scattered by spattering (as in the case of diarrhea) or rainfall. The larvae are taken in with vegetation during grazing and pass into the intestinal tract. They invade the intestinal wall, get into the lymphatic circulation and are taken to the lungs. They break out of the small capillary blood vessels and invade the lung tissue. Infrequently, they may pass through the lung and reach the uterus of a pregnant cow where they will invade the fetus and the calf will be born with lungworms. These larvae in the lungs will reach maturity in 3 to 6 weeks and begin laying eggs. Adult lungworms are about 2 to 3 inches long and most often are located in the dorsal posterior bronchi. In heavy infestations they invade other portions of the lung and are often seen in the trachea in large numbers. Lungworm counts of 3,000 up to as high as 20,000 worms in a single animal have been recorded. The trachea and bronchi of heavily infested animals usually contain a frothy, tenacious mucus that is characteristic of lungworm disease.
The differentiation of the pneumonia produced by lungworms and pulmonary emphysema or bacterial or viral pneumonia is not easy based on clinical signs. A postmortem examination will readily identify animals affected with lungworms. However, these animals often are affected simultaneously with emphysema and/or bacterial or viral pneumonia as a result of the lungworm infestation. Treatment of lungworm affected animals with antibiotics is of little help other than controlling the secondarily invading bacteria. When pulmonary emphysema is involved, the animal has an additional severe burden that often results in death.
Ordinarily an animal that survives the first attack will develop immunity. For this reason lungworm disease is called “self-limiting” – provided the animal survives the initial attack.
Lungworm larvae are affected by moisture and temperature. While they are greatly favored by adequate moisture and warm temperature, they are also quite resistant to the cold and lungworm larvae will live over the winter in latitudes as far north as Canada. Under favorable conditions larvae can survive on pasture over a year. However, the principal source of scar rover from one season to the next is carrier animals who reinfest the pasture. Under usual conditions there is a gradual buildup through the summer until the fall and early winter when the greatest number of cases appear.
The best protection against these parasites in Texas is hot, dry weather which the larvae are unable to withstand. For this reason, infestation with the parasite is usually listed to east Texas and the Gulf Coast area although it also appears on irrigated pasture elsewhere.
The parasite can bee controlled by management and this is a reason for discussing the life cycle of this parasite.
Fortunately, some of the newer drugs for parasites are effective against lungworms. An earlier developed one was effective against adults only but a more recent product (Levamisol) is also effective against larval forms.
A vaccine has been developed against this parasite by exposing larval forms to x-rays or a chemical. However, there is little demand for this product in Texas.
Ranchers who suspect this condition in their herd should consult their veterinarian to determine if the cause of the pneumonic symptoms observed is lungworms or one of the other types of pneumonia; divide if and when to treat cattle with one of the available drugs; and, what management practices to undertake to control reinfestation.
While these parasites are not as prevalent as stomach worms in Texas, it is a very serious problem in those herds that do become infested.