Estrosis is an entomotic disease that occurs in sheep as a result of infection with the larvae of the botfly. Parasites infect the animal's nasopharynx - they live in the frontal, maxillary sinuses, cavities of the horny processes, ethmoid bone, and in severe cases the brain is involved in the process. Intense inflammation of the epithelium of the upper respiratory tract, in the absence of diagnosis and treatment, can cause a decrease in productivity and death of livestock.
Description of the insect
Nasopharyngeal gadflies belong to the family Oestridae, a subfamily of insects from the order Diptera.In sources on parasitology, insects are described as flies about 12 millimeters long, with a yellow head and large black eyes. The color of the abdomen is blue, the legs are short and orange, the wings are transparent. The body of the gadfly is covered with fine hair, which is why it resembles a bumblebee. The oral organs are poorly developed.
A gadfly can live from three to twenty days, after which its weight decreases by a third. Under unfavorable climate conditions, the insect freezes, the life cycles inside its body slow down. Nasopharyngeal gadflies are viviparous. The female can spray the larvae directly in flight into the nostrils of the cattle in large quantities, from where they penetrate into the nasal and frontal sinuses and into the pharynx.
Parasite development stages
Gadflies are insects characterized by a closed chain of transformations. The complete life cycle is from the larva to the adult stage. The three stages of insect formation are distinguished by characteristic forms:
- The larvae of the first stage before molting reach 4-5 millimeters in length and 0.34 millimeters in width. They are whitish in color with two dark chitinous hooks at the anterior end and with numerous spines scattered throughout the body. With hooks, the larvae are firmly attached to the mucous membrane of the nasal concha and ethmoid bone, causing catarrhal and then serous-purulent rhinitis.
- At the second stage of development, the larvae molt, become white, their length is 5-12 millimeters, their width is up to 3 millimeters. In the spring, being in the frontal sinuses and cavities of the horny processes, the larvae molt again and turn into the third stage.The larva feeds on the tissues and fluids of the host’s body. It dissolves solid components with special dermatolytic enzymes.
- At the final stage of development, the parasite larva reaches sizes of up to 30 millimeters in length and 3-10 millimeters in width. At the posterior end of the larva's body there are two spiracles. When warm, stable weather sets in, the gadfly larva migrates in the opposite direction, entering the nasal cavity, from where, when the sheep sneezes, it falls to the ground, buries itself in the soil and pupates.
The pupa is painted dark gray, then acquires a brown tint. Its dimensions are 12 millimeters in length, 5 millimeters in width. At the upper end of the pupa there is a cap through which the adult, fully formed insect (imago) emerges. Development takes from two days to two weeks.
Symptoms of estrosis
Of the total number of larvae that have penetrated the mucous membrane of the sheep's respiratory tract, only about 20% reach the next developmental phases. The rest die and come out along with nasal mucus during the sneezing and snorting of the animal in the first stage. Invaded parasites attach themselves to the mucous epithelium, leading to its injury and intense inflammation, and the release of mucopurulent contents from the nasal passages.
The main sign that estrosis infection will soon begin among the rams is a noticeable change in the behavior of the livestock. The animals huddle together, look frightened and restless, shake their heads down, and move their limbs. 2-4 days after the female gadfly attacks the sheep, the larval development cycle begins.
The first symptoms of infection appear in livestock 5-6 days after infection. The main signs of estrosis include:
- frequent sneezing and snorting of sheep - this is how they try to free the nasal passages from the parasite larvae that have entered there;
- a sharp increase in the amount of exudate released from the nostrils - immediately after infection it has a mucous, liquid consistency, after which it becomes thick, mixed with pus;
- engorgement and swelling of the nose near the nostrils - a crust of drying serous-purulent discharge forms along their edges;
- difficulty breathing with constant snoring - observed due to narrowing of the lumen of the nasal openings, intense inflammation of the mucous membrane;
- enlargement of the submandibular lymph nodes;
- heat;
- deterioration of the animal's condition, loss of strength.
In the advanced stage of estrosis, the membrane of the brain is affected. Against the background of general intoxication and damage to brain structures, coordination of movements is impaired, and convulsive seizures are possible. Sick sheep lag behind the herd and make manege movements. In a severe form of the pathology, the animal experiences paresis (decreased muscle strength) and paralysis of the limbs; in the absence of treatment, death occurs after 3-5 days.
Diagnostic methods
An experienced veterinarian can diagnose estrosis in rams based on a combination of clinical signs. Sometimes a trial irrigation of the nasal passages with insecticidal solutions is required - in this case, the larvae fall out into the external environment. You can conduct an intradermal test (allergic research technique). Differential diagnosis is important - sheep oestrosis is often confused with coenurosis. But, unlike estrosis, with coenurosis animals do not experience a runny nose or nasal discharge, but only focal thinning of the skull.
Estrosis can be diagnosed after the death of a sheep - inside the mucous membrane of the respiratory tract there are larvae measuring 12-15 millimeters in size.
Treatment of estrosis
There are several effective drugs that have almost 100% effect against gadfly larvae:
- “Cyflunit Flock” is a preparation in the form of a spray with a volume of 500 milliliters, completely ready for use. It is enough to apply 7 milliliters of the product to the skin along the spinal column to provide 4 weeks of protection against insects;
- “Ivermec” is a medicine in injection form, which contains the component ivermectin and vitamin E. One injection of the drug is given, the second injection is repeated after 8 days. The substances are quickly absorbed, and there are no seals or abscesses at the injection site. In addition to gadflies, the product is used to combat nematodes that attack the stomach and intestines, lice, and ticks;
- “Clozatrem” is an injection-type drug based on closantel. Thanks to this component, already 10 hours after the first injection you can get rid of infestation by gadfly worms, nematodes, trematodes and other parasites;
- “Butox” is a product with insecticidal and acaricidal properties. It is a light yellow oily liquid that dissolves in water. The drug is used in diluted form, by spraying or bathing.
Timely initiation of estrosis therapy will eliminate larvae in the nasal sinuses of sheep, minimize the clinical manifestations of the disease and prevent livestock mortality.
Prevention of occurrence
To prevent estrosis in sheep, it is recommended to regularly inspect livestock areas for pupae and adult gadflies.It is useful to install shields for planting insects near the flocks, having previously treated them with whitewash with the addition of insecticides.
Early treatment of livestock with Clozatrem or Ivermek will protect sheep from attacks by gadflies. Protective equipment should be used and pens should be inspected for the presence of pupae and adult insects regularly from May to September.