Lice: chewing and sucking species

Sucking and chewing lice occur on cattle around the world.  The life cycle is direct and all life cycle stages - adults, eggs (nits), larvae and nymphs occur on the host.  Although transmission is likely most common animal to animal, lice can also be spread through the environment and by inanimate objects, for example grooming equipment.  In cattle in Canada the prevalence and intensity of lice infestations peak during the winter and are low during the summer.  During the summer, however, a few animals in a group retain lice populations and serve as the source of infestation in the fall.  This seasonal pattern is thought to be due to crowding of cattle during the winter, increasing the opportunities for transmission, and the spring loss of the winter hair coat, and the high skin surface temperatures during the summer that impede reproduction by the lice.  The major significance of lice infestations in cattle are irritation, hair loss (a real problem at very low winter temperatures), and blood loss with high burdens of sucking lice and sometimes concurrent disease or other stresses.  Lice are relatively host-specific and species from cattle very rarely infest people.

 

LICE IN SHEEP

There is little information on the occurrence of lice on sheep in Canada. In the US, the chewing louse is Damalinia ovis and the sucking lice Linognathus ovillus and L. pedalis. The biology of these species is similar to those on cattle, except that L. pedalis is most often found on the lower limbs, and may be associated with lameness.  There are no products approved in Canada for lice in sheep.

LICE IN GOATS

There is little information on the occurrence of lice on goats in Canada. In the US, the chewing louse is Damalinia caprae and the sucking lice Linognathus stenopsis. In addition, D. ovis will apparently transmit between sheep and goats. The biology of the species on goats is similar to those on cattle.  There are no products approved in Canada for lice in goats.

More general information on lice is available under Cattle.

Phylum: Arthropoda
Subphylum: Uniramia
Class: Hexapoda
Subclass: Pterygota
Order: Mallophaga (Chewing Lice)
Order: Anoplura (Sucking Lice)

Other arthropods of veterinary importance within the Subclass Pterygota are bugs (Order Hemiptera), fleas (Order Siphonaptera) and flies (Order Diptera).

The mallophagan of cattle in Canada is Damalinia (Werneckiella) bovis (sometimes referred to as Bovicola bovis), and the anoplurans are Haematopinus eurysternus, Linognathus vituli, and, rarely, Solenopotes capillatus.

Larval and adult lice are dorso-ventrally flattened and have six legs arising from the thorax. The legs terminate in claws. Adult L. vituli, and H. eurysternus are up to approximately 5 mm in length. Adult Damalinia (Werneckiella) and Solenopotes capillatus are smaller than the other genera.

In common with other chewing lice, the head of D. (W.) bovis is wider than the thorax, is blunt anteriorly, and has two prominent, segmented antennae, one on each side.

The heads of the sucking lice are narrower than the thorax, are pointed anteriorly, and have two prominent, segmented antennae, one on each side.

The eggs (nits) of both chewing and sucking lice are whitish in colour, measure up to approximately 750 µm by 300 µm, and are fixed to the hairs usually quite close to the skin surface. Louse eggs are readily visible to the naked eye, particularly if present in large numbers.

 

Various species of chewing and sucking lice occur on cattle around the world. In western Canada, D. (W.) bovis and L. vituli are common, particularly in younger animals. Haematopinus eurysternus and S. capillatus are found less often.

Lice infestation in cattle in Canada is usually a winter problem, when prevalence and intensity of infestations peak. Most animals lose most of their lice in the spring. Lice are relatively host specific, so cattle lice are only very rarely found on other animals or on people.

For the chewing and sucking lice of cattle, the entire life cycle occurs on the host. Adult females lay eggs (nits) attached to hairs. A larva develops in each egg, which hatches and develops through three nymphal stages before becoming an adult. All the larval stages, the nymphs and the adults all feed on the host, chewing lice primarily on skin debris, sucking lice on blood and tissue fluid. The life cycle is completed in a few weeks. Lice probably cannot survive off the host for more than a few days

Life Cycle: Chewing and Sucking Lice

Cattle lice are transmitted among their hosts primarily by direct contact, although fomites such as fences, posts and bedding can play a minor role. A key feature of the epidemiology of cattle lice is the increase in levels of infestation over the winter, and the loss of louse populations in the spring.

It is believed that carrier animals that maintain relatively high numbers of lice over the summer, often in the ears, the groin and the tail brush, act as the source of infestation in the fall and winter. During this period transmission is enhanced by the crowding associated with winter accommodation and the stresses of an adverse climate and perhaps pregnancy.

Explanations for the spring loss of lice by most animals are less certain. Certainly, portions of populations of all life cycle stages will be lost as the winter hair coat is shed, and it has also been suggested that the increase in environmental and skin surface temperatures in the spring reduces the parasite’s ability to reproduce as well as the survival rates of the immature stages.

Many cattle infected with lice, particularly in low numbers, show no detectable clinical signs. Both chewing and sucking lice can, however, cause irritation which leads to attempts by the cattle at relief. This may result in hair loss from excessive grooming, rubbing and damage to the skin. The anoplurans suck blood, which in heavy infestations may cause a clinically apparent anemia. Lice infestations, particularly if heavy, may lead to sub-optimal production by interfering with feeding and reducing the infested animal’s insulation, potentially a major problem in Canadian winters.

Unexplained Pruritus and Alopecia in Cattle in Western Canada

In recent years in western Canada there have been many reports by producers and veterinarians of pruritus and/or patchy alopecia in cattle, usually in the late winter or spring. Many affected animals had been treated the previous fall with an endectocide, primarily for lice, and these, or perhaps mange mites, are often suspected as the cause for the subsequent clinical skin problems in the cattle.

Many of these occurrences have been intensively investigated, often by the pharmaceutical companies, and in only a very few have ectoparasites been detected. Histological examination of skin biopsies usually reveals only hair loss, sometimes with a mild eosinophil infiltration. The causes of most cases of this condition remain a mystery.

History and clinical signs are helpful, but the recovery of adult lice (which can be identified microscopically to species) or of eggs are definitive.

There are several products approved in Canada for louse treatment in cattle.  Currently, among the endectocides only the topical (pour-on) preparations are effective against both chewing and sucking lice.  The injectable formulations are effective against sucking lice. Some endectocides provide lengthy periods of protection following treatment, and during which it is difficult or impossible to establish new infestations on treated animals.

Endectocide Products for Lice

Drug	Product	Preparation(s)
Doramectin	DECTOMAX	* Topical and Injection
Eprinomectin	EPRINEX	* Topical
Ivermectin	VARIOUS	* Topical and Injection
Moxidectin	CYDECTIN	* Topical and Injection

* Only topical (pour-on) preparations are effective for chewing lice

Other Topical Products for Lice

In Canada the use of all these products is controlled by the Pest Control Products (PCP) Act.  When using these products, it is important to be familiar with any restrictions.

Drug	Product	Chewing and/or Sucking
Carbaryl	DUSTING POWDER, SEVIN	Unstated
Cyfluthrin	CYLENCE POUR ON INSECTICIDE	Chewing and Sucking
Lambda cyhalothrin	SABER POUR ON INSECTICIDE	Chewing and Sucking
Malathion	CO-OP BACKRUBBER CONCENTRATE,  MALATHION	Unstated
Permethrin	BOSS POUR ON, DELICE POUR ON,  ECTIBAN, VETOLICE	Varies with product - check the labels
Pyrethrins	ABSORBINE FLYS-X	Sucking

Additional information is on the products mentioned is available from the Compendium of Veterinary Products (Twelfth Edition, 2011), or from the manufacturers.

When treating for lice, it is very important to treat all animals in a group.  Also, all new additions to the gorup must be treated.

Lice are relatively host specific, so human infestation is not a concern.

Cortinas R et al. (2006) Ectoparasites of cattle and small ruminants. Veterinary Clinics of North America Food Animal Practice 22: 673-693.