External parasites and skin disease treatment and control in cattle

12/10/2022

Insects such as stable flies, house flies, horn flies, face flies, mosquitoes, horse flies, deer flies, cattle grubs, and lice as well as ticks and mites are the major external parasites of dairy animals in the United States. These pests cause obvious discomfort to livestock and economic effects of heavy populations usually are discerned easily. However, research efforts to date have failed to establish reproducible losses caused by specific ectoparasites. Research efforts involving a multidisciplinary systems approach are necessary to provide the data needed to develop total dairy management programs.

10/09/2022

Beef cattle production represents a multibillion dollar industry in the southeastern United States. External parasites (ectoparasites) are those that live and feed on the outside of the animal. These pests directly affect the producer’s bottom line by causing decreased weight gain, decreased milk production, loss in hide value, and potential disease transmission. Lack of external parasite control costs beef producers billions of dollars each year.
Integrated Pest Management
To be successful in the control of external parasites, producers need to take an integrated approach to pest management. Integrated pest management (IPM) uses a variety of pest control tactics (biological, cultural, and chemical control) to reduce overall pest pressure. IPM strategies are pest specific and will vary based on the biology of the pest you are trying to control; therefore, proper pest identification should always be the first step in the process.
Biological Control
Proper identification of insect populations is imperative to make sound pest control decisions, as many of the insects that we encounter are harmless to both humans and animals. Some insects are even beneficial in the fight against common cattle pests either through predation or competition for resources. Examples include black dump fly larvae, which are known to feed on house fly larvae developing in the same manure. Soldier fly larvae will outcompete horn fly and house fly larvae for food, which leaves the pests without the necessary resources to fully mature. Some of the more commonly discussed biological controls in livestock operations are dung beetles and parasitic wasps. Dung beetles will actively remove manure, making the pats dry faster and the environment unsuitable for fly development. Several species of parasitic wasps, marketed as biological controls of cattle pests, are commercially available. The wasps lay eggs inside immature horn flies, house flies, and stable flies. The wasp larva then eats the immature flies. It should be noted that wasps can be used to supplement sanitation but probably will not control pests below economic thresholds. This is especially true when the environment favors pest development.
Cultural Control
Cultural controls are practices that manipulate the pest’s environment to reduce conditions that are suitable for development. Make sure to quarantine and treat new animals before they are introduced into the herd to reduce chances of lice, mite, or tick infestations. Reducing breeding conditions through proper management and sanitation is the most effective way to control cattle pests.
Use hay rings or roll out hay to reduce waste. Trampled hay that is urinated or defecated on is the primary breeding site of many cattle pests.
Avoid feeding hay in the same location each time.
Use pasture rotation and proper stocking rates to allow manure to dry out and decompose.
In areas where cattle congregate, remove manure and spread thinly on pastures to allow it to dry properly.
Remove and dispose of carcasses quickly and properly.
Keep pastures cut or properly grazed to decrease thatch and associated moisture, which aid in pest development.
Keep water troughs clean and in proper working order. Eliminate areas that hold stagnate water to reduce mosquito breeding sites.
Chemical Control
Many pesticides are available that are labeled for external parasites of beef cattle. Pesticides should be used only when other methods are ineffective or unavailable. Economic thresholds, the point at which chemical control measures are economically justified, should be used when making treatment decisions. Always read and follow label directions. The pesticides listed in this document are meant only as a reference guide, not as full label directions or recommendations.
Insecticide Application Methods
Dips
Dip vats are used to treat a large number of animals in an efficient manner. Vats provide good coverage of the animal being treated to ensure effective control. Use only products labeled for dip vat treatments and follow directions when filling and recharging.
Dusts
Most commonly, dusts are applied using self-treatment dust bags that are recharged throughout the season. Place dust bags in areas where animals are forced to use them: heading toward feed troughs, waterers, and mineral feeders, for example. Dust bags are most effective when placed at the animals shoulder height. Placing dust bags under cover will allow them to stay dry and prevent caking.
Ear Tags
Ear tags deliver slow-release insecticide over time via a plastic tag placed in the ear of the animal. Ear tags typically control flies for 3 to 5 months and ear ticks for 4 to 5 months. They do a good job of controlling horn flies, stable flies, lice, mosquitoes, and ticks. Follow the label in regard to the number of tags per animal. Most brands require two tags per mature animal; applying fewer than the recommended rate will not save money but will increase pest resistance to the insecticide.
Feed-Throughs
Feed-through products are insecticides that are mixed with either feed or mineral supplements. They pass through the animal’s digestive system and control immature flies developing in the manure. Adult flies will migrate from nearby herds, so feed-through products are most effective when the herd is isolated from other herds or used in addition to a topical treatment method. Consistent intake is imperative, so animals need unlimited and continual access to the feed/mineral for the products to be effective. Feed-throughs take time to build up in the system and become effective, so make sure to follow the label about when to start (typically 3 to 4 weeks before fly season) and finish feeding products during the fly season. Feed-through insecticides are not digested, so the products never get into blood or meat; therefore, they have no effect on adult flies.
Injectables
Some active ingredients are formulated for sucutaneous injection in beef cattle. These products are labeled for cattle grubs and lice as well as for internal parasite control.
Pour-Ons
Pour-on products are made to be applied down the length of the animal’s backline and sometimes down the center of the face. They are then absorbed into the skin and act as systemic insecticides. They may control horn flies for up to 30 days.
Spot-On
These systemic products are applied to a specific area along the animal’s back. They require specially designed applicators and are most effective for control of cattle grubs and lice.
Sprays
Sprays are meant to be applied as a coating across the entire animal. Only mix and prepare the amount needed to treat the number of animals. Do not store or use mixed insecticides. Emulsifiable concentrates or soluble formulations are well suited for small sprayers. Wettable powders require a high-volume piston pump sprayer with agitator. For ticks, lice, and mites, use enough water to cover the animal thoroughly. When spraying systemic insecticides to control cattle grubs, be sure to wet the animals to the skin.
External Parasites of Beef Cattle in the Southeast
Horn Fly
Close up of horn flies (Haematobia irritans) on a black cow.Horn flies (Haematobia irritans) are one of the most economically important pests of beef cattle in the United States. Adult horn flies are small (3/16 inch) and are similar in color to house flies. They spend most of their adult life on the animal (back, sides, and belly) where they feed on blood 30 to 40 times per day, using piercing mouthparts that inflict a painful bite. Their persistent biting causes cattle to react with evasive maneuvers (tail flicking, side licking, stomping, kicking their bellies, huddling together). Cattle spend more time trying to rid themselves of horn flies than they do eating or drinking, leading to weight loss, decreased milk production, dehydration, and weakness. Adult horn flies live about 3 weeks and leave the animal only to lay eggs under the edge of fresh manure pats. Development takes approximately 10 to 20 days. When horn flies exceed the economic threshold of 200 flies per side, weight gain will be affected, and calves can lose up to 15 percent of their body weight. Use of chemical controls is necessary once this economic threshold is reached
Chemical control options come in a variety of delivery methods: back rubs, dust bags, ear tags, feed-throughs, injections, pour-on liquids, and sprays. Different delivery methods will work depending on your herd management plan. Make decisions based on your system.
Wait to use topical control measures until you reach the 200 flies per side economic threshold.
Rotate chemical classes of insecticides each season to prevent resistance.
Remove ear tags at the end of each fly season or when the tags become ineffective (economic threshold is reached).
Avoid combination ear tags because they promote resistance to multiple insecticide classes simultaneously.
Place back rubs and dust bags in areas where cattle are forced to use them; good examples are gates that cattle must go through to access water, feed troughs, or mineral feeders. It may take time for cattle to become acclimated to these devices.
When using insect growth regulator feed-through products, begin to feed early in the spring and feed through the first frost. Consistent intake is essential, so make sure animals have constant, equal access to the product.
Stable Fly
Stable flies (Stomoxys calcitrans) have a major economic impact to the US cattle industry. Adults feed on the blood of the animal and are painful biters. Unlike horn flies that stay on the animal, stable flies will feed once per day and then leave the animal to rest on nearby surfaces (vegetation, barn walls, etc.). Adults are similar in size to house flies (about 1⁄4 inch long), and they lay their eggs in decaying vegetation that has been mixed with urine or f***s. Stable flies will attack the legs, sides, backs, and bellies of cattle, causing evasive maneuvers (stomping, belly kicking, tail switching, bunching). Cattle spend more time trying to rid themselves of flies than eating or drinking, leading to weight loss, decreased milk production, dehydration, and energy loss. Extreme bunching can also reduce the cattle’s ability to dissipate heat during the hot and humid days of summer. Chemical control action must be taken when the economic threshold of two to four flies per leg is noted
Remove old or trampled hay bales.
Use hay rings to reduce waste and to reduce amount of hay that will be trampled, urinated, and defecated on.
Rotate hay feeding locations to reduce accumulation and to allow previous hay feeding locations to dry properly.
Remember that biological controls that attack horn fly larvae will also attack stable fly larvae.
Spray animals and resting sites with approved insecticides to provide immediate control.
Pesticide Suggestions for Horn Flies and Stable Flies
a comprehensive list of available chemical control products labeled for horn flies and stable flies. Alabama Extension does not promote one product over another. Make sure to read and follow all label instructions and guidelines. The table is organized by insecticide formulation, then by class of insecticide. Rotation between insecticide classes is key to successful resistance management.

10/09/2022

Treatment and Prevention of Lumpy Skin Disease in Cattle
Attenuated virus vaccines may help control spread
The spread of lumpy skin disease in recent years beyond its ancestral home of Africa is alarming. Quarantine restrictions have proved to be of limited use. Vaccination with attenuated virus offers the most promising method of control and was effective in halting the spread of the disease in the Balkans.
Administration of antibiotics to control secondary infection and good nursing care are recommended, but the large number of affected animals within a herd may preclude treatment.

10/09/2022

Lumpy skin disease is an infectious, eruptive, occasionally fatal disease of cattle characterized by nodules on the skin and other parts of the body. Secondary bacterial infection often aggravates the condition. Traditionally, lumpy skin disease is found in southern and eastern Africa, but in the 1970s it extended northwest through the continent into subSaharan west Africa. Since 2000, it has spread to several countries of the Middle East and in 2013 extended west into Turkey and several countries in the Balkans. More recently, outbreaks of lumpy skin disease were reported for the first time in Georgia, Russia, Bangladesh, and the People's Republic of China. The recent geographic spread of lumpy skin disease has caused international concern. The disease has not been recorded in the Western hemisphere or in Australia or New Zealand.

10/09/2022

Lumpy skin disease is a viral infection of cattle. Originally found in Africa, it has also spread to countries in the Middle East, Asia, and eastern Europe. Clinical signs include fever, lacrimation, hypersalivation, and characteristic skin eruptions. Diagnosis is by histopathology, virus isolation, or PCR. Attenuated vaccines may help control outbreaks.

10/09/2022

Unfortunately there are no specific antiviral drugs available for the treatment of lumpy skin disease. The only treatment available is supportive care of cattle. This can include treatment of skin lesions using wound care sprays and the use of antibiotics to prevent secondary skin infections and pneumonia. Anti-inflammatory painkillers can be used to keep up the appetite of affected animals. Intravenous fluid administration may be of benefit; however this may not be practical in the field. The lack of treatment options for lumpy skin disease virus emphasizes the need of using effective vaccination for preventing disease.

10/09/2022

Ringworm Treatment in cattle
Ringworm will usually heal itself without treatment, however this can take up to nine months.
Topical treatment, application of the medication directly onto the lesion, is the usual procedure. Medication cannot pe*****te the crusts; the crusts should be removed by scraping or brushing. They should be collected and burned to avoid contaminating the premises. Lesions should be treated at least twice, three to five days apart.

10/09/2022

Ringworm in Cattle
Cause
Ringworm is one of the commonest skin diseases in such cattle. Ringworm is a transmissible infectious skin disease caused most often by Trichophyton verrucosum, a spore forming fungi.
The spores can remain alive for years in a dry environment. It occurs in all species of mammals including cattle and man. Although unsightly, fungal infections cause little permanent damage or economic loss. Direct contact with infected animals is the most common method of spreading the infection.

10/09/2022

Trichophyton verrucosum is the usual cause of ringworm in cattle, but T mentagrophytes, T equinum, Microsporum gypseum, M nanum, M canis, and others have been isolated. Dermatophytosis is most commonly recognized in calves, in which nonpruritic periocular lesions are most characteristic, although generalized skin disease may develop. Cows and heifers develop lesions on the chest and limbs, and bulls develop lesions in the dewlap and intermaxillary skin. Lesions are characteristically discrete, scaling patches of hair loss with gray-white crust formation, but some become thickly crusted with suppuration. Dermatophytosis as a herd health problem is more common in the winter and is more commonly recognized in temperate climates.
Dermatophyte infection, cow
Dermatophyte infection, cow
COURTESY OF DR. KAREN A. MORIELLO.
It is not cost effective to treat cattle with oral antifungal medications. Treatment involves improvement of husbandry because overcrowding increases disease prevalence. Remove crusts with a brush and discard the brush and burn the infective material. Topical therapy is the treatment of choice, with lime sulfur 1:16 or enilconazole 1:100leave-on rinses. Do not use bleach, because this can be irritating and a human health hazard. Twice-a-week treatment is recommended if this is practical. Dermatophytosis will self cure in animals.
A live-attenuated fungal vaccine is in use in some countries; it is not available in North America. The vaccine has been used in control and eradication programs to successfully decrease the number of new infected herds. The vaccine prevents development of clinical lesions and transmission to other animals. Vaccination can reduce the incidence of zoonotic disease in farmers, their households, veterinarians, and people working in slaughterhouses and tanneries.

10/09/2022

Control of the “bug” is through proper herd management. Abscesses are allowed to mature and then lanced and flushed with an iodine solution. All material that comes from inside the abscess and material it touched should be burned and the animal isolated until the lanced abscess is completely healed over. The best way to keep a clean herd is to not bring in infected animals, and if an abscess is found, cull the animal since it is a recurring disease. C. pseudotuberculosis is sensitive to penicillin, however due to the way an abscess grows, antibiotics do not get through the chambers to kill the bacteria.

10/09/2022

Ulcerative lymphangitis in cattle and horses causes an infection in the lower limbs with abscesses in the pectoral lymph nodes, and contagious open sores. This is one of the most common infectious diseases of horses and cattle in the western states. It generally heals without treatment or with limited topical help. C. pseudotuberculosis contracted through skin wounds like IM injections, stable flies, and contact with contaminated equipment. In the southwest United States, it seems to be seasonal, with the largest incidence in late summer to fall.

11/07/2021

30/06/2021

In autumn 2006, Finnish meat inspection data revealed lesions in tendons, muscles and ligaments of bovine hind legs leading to partial condemnation of carcasses. In gross pathological examination at Finnish Food Safety Authority Evira, Oulu (now Fish and Wildlife Health) Research Unit, Onchocerca sp. (Filarioidea; Onchocercidae) nematodes were detected in lesions. Due to this, a pilot study was made in order to find out what filarioid nematodes do occur in cattle, horses and sheep in Finland.

Methods
Ventral skin biopsies from 209 dairy cattle and 42 horses, as well as blood samples from 209 cattle, 146 horses and 193 sheep, were collected from different parts of Finland and examined for microfilariae. Visceral organs and other tissues from 33 cattle with parasitic lesions were studied histopathologically.

Results
Onchocerca sp. microfilariae (mf), 240 μm long, range 225–260 μm, 5.4 μm thick, were found in 37% of the skin biopsies of cattle. All blood samples from cattle, horses and sheep and skin biopsies from horses were negative for mf. Ventral skin microfilaria prevalence in cattle was higher in southern Finland than in the North (p = 0.001). Animal age and sampling time was not associated with mf prevalence. The infection was evenly distributed among young and older animals. Macroscopic lesions on tissues included greenish-grey discolouration and often oedema. In most of the lesions, small pale nodules were seen on the fasciae. Histopathologic examination of the samples revealed mild to intense infiltration with eosinophilic granulocytes and multifocal nodular lymphoplasmacytic aggregations were seen. In some samples, there were granulomatotic lesions with central necrotic tissue and cell detritus, surrounded by eosinophilic granulocytes, lympho-, plasma- and histiocytes and some multinucleated giant cells. Around living nematodes no or only weak inflammatory changes were observed.

Conclusion
Onchocerca sp. infection in cattle was found to be common in Finland, but the amount of pathological changes leading to condemnation of infected parts is low compared to the mf prevalence. Pronounced pathological changes are distinct but rare and mild changes are difficult to distinguish. No other filarioid nematodes were observed from the animals and it appears that horses and sheep may be free from filarioid nematodes in Finland.

Background
Filarioid nematodes are known to occur among domestic animals almost all over the world. The economically most important and also most abundant filarioid nematodes in cattle are Setaria digitata, S. labiatopapillosa, S. marshalli, Onchocerca gibsoni, O. gutturosa, O. armillata, O. lienalis, O. ochengi, Parafilaria bovicola and Stephanofilaria spp. Generally, species of Onchocerca are medium-sized filarioids which usually inhabit subcutaneous tissues, ligaments and aponeuroses of large mammals whereas species of Setaria are found in the abdominal cavities of artiodactyls. The filariids (Parafilaria and Stephanofilaria) are small to medium-sized subcutaneous parasites of certain mammals. All filarioid nematodes produce larvae (microfilariae, mf) into the skin (Onchocerca spp., Parafilaria spp. and Stephanofilaria spp.) or blood circulation (Setaria spp.) of the host where they are available to the haematophagous insects which operate as intermediate hosts and active vectors for the parasites [1].

In their normal definitive hosts, most species of filarioid nematodes are often very well adapted and they are well tolerated [2]. For example Onchocerca spp. of African cattle are generally believed to have a low pathogenicity [3]. Usually the damage caused by filarioid worms is the result of chronic inflammatory reactions around dead or dying worms or mf. Dead worms in the subcutaneous tissues usually become calcified and surrounded by dense fibrous tissue, causing little damage, but they may also act as a focus for bacteria and abscesses may develop in onchocercal nodules [2].

Parafilaria bovicola (Filarioidea; Filariidae) occurs in cattle mainly in Europe and Africa and causes cutaneous bleedings in live cattle and bruise-like lesions in the subcutaneous and intermuscular surfaces of affected carcasses [4]. In Sweden, P. bovicola was well established in the 1980's and since then has been responsible for substantial economic losses in beef production [5]. In Sweden it utilizes the face fly (Musca autumnalis) as a vector [6].

Stephanofilaria spp. are small filariid nematodes found in the subcutaneous tissues of bovids and cause sores and dermatitis in cattle in India, Malaysia and the U.S. [1]. The disease, stephanofilariosis is characterized by one or more circular or oblong areas of scaly, depilated, crusted skin at or near the umbilicus [7]. Stephanofilaria is transmitted by the horn fly Haematobia irritans. There are also indications of stephanofilarosis causing summer sore in cattle in Finland but the matter has not been thoroughly studied [8].Setaria labiatopapillosa is a common cosmopolitan parasite in the abdominal cavity of cattle, while S. digitata is found in Asian cattle. They are considered non-pathogenic [1, 9]. However, immature stages of S. digitata invade the central nervous system of horses, sheep and goats causing lumbar paralysis and other CNS symptoms generally called cerebrospinal nematodosis [10].

Horses are commonly infected with Setaria spp. nematodes in Asia, Europe and America [11–13] and worldwide with Onchocerca spp. [14, 15]. According to a report [16], Onchocerca cervicalis was fairly common among horses in Finland in the 1940's. Onchocerca infections of horses are most commonly seen clinically as a condition called fistulous withers [17].

Parafilaria multipapillosa is a parasite of the subcutaneous and inter-muscular connective tissues of horses in Eurasia, Africa and South America. Infection with the parasite results in condition known as "bloody sweat" or "summer bleeding" [1].

In North America a filarioid nematode, Elaeophora schneideri, lives in the arteries of domestic sheep [18]. Mule deer (Odocoileus hemionus) is believed to be the main definitive host of the worm which occurs also in other cervids [19]. Elaeophorosis caused by Elaeophora elaphi has also been found in the hepatic vessels of red deer (Cervus elaphus) in Europe [20]. In an aberrant host, like sheep, the skin dwelling microfilariae cause clinical sings in the form of dermatoses and pathological changes in retina and in the nasal and oral mucosa. The adult worms, on the other hand, damage the arteries where they live in [21]. Similar arterial damage is found in cattle associated with Onchocerca armillata and Elaeophora spp. infections in Tanzania [22].

Filarioid nematodes and their impacts on wild and semi-domesticated cervid ruminants have been under intense interest in Finland during the past few years. Attention to these nematodes was drawn in 2003 when there was an outbreak of peritonitis in reindeer caused by the nematode Setaria tundra (Filarioidea; Onchocercidae), the definitive host of which is assumed to be roe deer (Capreolus capreolus) [23]. The outbreak lead to economical losses to reindeer herders and it impaired meat hygiene. Recently, a new yet unidentified species of filarioid nematode was found in the lymphatic vessels of cervids (Laaksonen et al., unpublished). This new species is abundant especially among reindeer.

All filarioid nematodes are transmitted by haematophagous vectors. In temperate zones the transmission occurs in summer when the vectors are active [24]. Recent studies (Laaksonen et al., unpublished) give rise to the hypothesis that the currently high prevalence of filarioid nematodes in some animals in Finland may be associated with the ongoing climate change.

The detrimental effects of these filarioid outbreaks to the health and well-being of cervids, as well as to meat hygiene, raised questions about the impacts of filarioid nematodes on other meat production animals (cattle, sheep and horses). Studies on this area are scarce in Finland. Recent meat inspection data in autumn 2006 from Kuopio slaughterhouse revealed parasitic lesions in cattle and in examination at Finnish Food Safety Authority Evira, Oulu (currently Fish and Wildlife Health) Research Unit, Onchocerca sp. nematodes were found. Filarioid nematodes could posses a threat against meat producing animals and inflict economical losses to the meat and dairy industries. Therefore, elucidation of the filarioid situation in Finland was considered necessary.

The main aim of the study was to find out the species of filarioid nematodes occurring in cattle, sheep and horses in Finland, and their prevalence. The intention was to determine if the species causing pathological changes in slaughter cattle are the same as infecting cervids, and to describe infection dynamics.

Methods
Material from cattle, sheep and horses was collected between 28 February and 24 September, 2007. Blood and skin samples from the animals were collected from slaughterhouses at Kuopio (Atria) (28.2.-14.6.07, 150 cattle skin samples of 17734 slaughtered), Kemi (Veljekset Rönkä Oy) (17.4.-22.5.07, 59 cattle skin samples of 673 slaughtered, 15.5.-24.9. 07, 193 sheep blood samples of 1104 slaughtered and 13 horse blood and skin samples) and Hautjärvi (Hannu Vainio Oy) (29 horse skin samples). In addition, blood samples from horses (133) were collected at different horse clinics by practising veterinarians in Oulu (17), Hyvinkää (21), Ypäjä (18), Lahti (19), Laukaa (20), Ylivieska (18) and Tampere (20). Blood samples from horses were mostly from half-breed trotters or mounts (riding-horses) visiting clinics for some undefined reason. Cattle and horse samples originated from all over Finland and sheep from the provinces of Lapland and Oulu. In slaughterhouses, samples were taken from all slaughtered horses during collecting period and cattle and sheep samples were collected randomly when labour was available. All the animals included in this study were over one year old and had been grazing outdoors in the previous summer and thus had been exposed to the potential vectors of filarioid nematodes. Blood samples were taken from all of the animals. Skin biopsies were taken from 209 cattle and from 42 horses. Tissue samples from 33 cattle (not included in the blood and skin monitoring) with lesions considered parasitic (subcutaneous and subfascial oedema and granulomas with greenish or yellowish coloration indicating eosinophilic infiltration, fibrotic or granulomatous fibrin depositions on visceral organs, especially on liver) were collected by the meat inspecting veterinarian during routine meat inspection from Kuopio slaughterhouse from 8 November, 2006, to 23 May, 2007. Tissues were delivered fresh to Evira, where they were dissected under stereo microscope for adult parasites, fixed in 10% neutral buffered formalin and routinely processed; embedded in paraffin, cut in 4 μm sections and stained with haematoxylin and eosin, and examined histopathologically. Samples included muscles and fasciae, tendons or ligaments of legs, flank or brisket from 24, liver samples from ten, lung samples from four and a spleen sample from one animal.

Blood samples were taken in 10 ml tubes (Venoject II, EDTA (K2): 19.5 mg, Terumo Europe N.V., Belgium). In laboratory, the examination for blood microfilariae was done by modified Knott's technique as described elsewhere [23].

Altogether 209 skin samples were collected from cattle (ages between 14 to 143 months). Skin samples were taken at the umbilical area following the examples given in literature [3, 9]. In the beginning of the sample collection, also ear skin biopsies were taken from the first 60 animals but the procedure was discarded due to obviously lower sensitivity. Skin biopsies approximately 1 cm2 in size were washed in tap water and cut into ten pieces with scissors. The pieces were incubated in fresh physiological saline for 24 h at room temperature (21–25°C). The tissues were discarded and microfilariae were concentrated by centrifugation for 12 minutes at 1600 g. The microfilariae were stained with 1% methylene blue and measured (n = 20).

Statistical analyses were made with Stata 9 (StataCorp, LP, USA) software. Finland was divided into two parts, North (Provinces of Lapland and Oulu) and South, in order to examine the spatial distribution of mf prevalence. The effect of age (group 1;