Public Health Importance

FIGURE 18.22 Hypochrosis hyadct-ria (Geometriciae) feeding at open wound of zebu. {Photo by Hans Bänziger.)

sugar-rich juices within. Other moths closely related to Calyptm are fruit piercers, suggesting that blood-feeding is a relatively recent development in this group, derived from such fruit-piercing behavior.

A number of Calyptm species have been observed piercing mammalian skin under natural conditions. Five Calyptra. species are known to feed on humans: Calyptra bicolor; C.fcisciata> C. opbiderotdes, C. pnrvct (Fig. 18.23), and C. pseudobitolor. Calyptra species also have been observed piercing the skin of elephants, water buffalo, zebu, Malayan tapir, rhinoceros, deer, antelope, mules, and pigs. The feeding times typically range from 3 to 15 min. The reaction to the proboscis penetrating the skin varies from being barely felt to causing locally intense pain accompanied by a burning sensation. The latter has been attributed to saliva which is introduced as the moth feeds.

FIGURE 18.23 Skin-piercing moth, Calyptra parva (Noctuidae), feeding on human. (Photo by Hans Banziger.)

The severity of reactions to urticating caterpillars is highly variable, depending on the species involved, the degree of contact, and the nature of the toxin. Toxic components commonly include histamine-iike or histamine-releasing substances which cause edema and wheal formation at the site of contact; proteolytic enzymes and esterases; peptides and other substances that can increase vascular permeability, destroy blood cells, or cause local necrosis of tissues; and globulins with immunologic properties.

Many cases involve mild, localized dermatitis in the form of a nettling sensation or minor irritation with transient puffmess or redness at the contact site. In more severe encounters, individuals often experience an intense burning sensation with associated wheal formation and persistent erythema. Other cases may include localized numbness, formation of vesicles, nausea, vomiting, or fever. In cases such as those involving the saddleback caterpillar and puss caterpillar, the affected skin tends to glisten after several minutes as fluids from the damaged dermal cells seep onto the skin surface. Without treatment, the burning sensation usually subsides within 30 min to an hour but may persist much longer. Radiating pains and lymph adenopathy may occur in more severe cases involving the limbs. The pain often extends proximally to the axillary or inguinal lymph nodes, sometimes with associated inflammation of the lymphatic vessels which may be visible as reddened traces on the skin surface. Some cases result in dull, throbbing aches in the lymph nodes which can persist as long as 12—24 hr. The contact site may remain discomforting and sensitive to touch for several days thereafter as the skin heals. The pattern of actual contact with the urticating spines may be evident for days, sometimes weeks.

Occupational erucism is a common occurrence in tropical countries, notably in South America and Southeast Asia, where field workers are exposed to stinging caterpillars. In addition to causing temporary discomfort and annoyance affecting primarily the arms and hands, chronic contact with some species (e.g., the arctiid Fremolis semirrufa in Brazil) can result in persistent swelling and fibrous lesions of the joints of the hands and fingers. Workers in saw mills may experience dermatitis as a result of contact with urticating hairs in egg masses on the trunks of trees being cut for timber or stored at mill sites.

Reactions to adult moths usually occur as dermal irritation induced by airborne setae on contact with the skin, a condition called moth dermatitis. Most of the reported cases involve Hylesia species. The response is similar to that caused by urticating larvae. The most commonly affected parts of the body are the face, neck, and upper limbs. As the setae are rubbed into the skin, they may release histamine-like substances that cause erythema and pruritus. The problem is further aggravated and spread by scratching and sweating or by clothing and bedding contaminated with the irritating hairs. In severe cases, symptoms may persist for several days or longer, sometimes resulting in fever, insomnia, malaise, nausea, vomiting, or muscle spasms.

When airborne body setae or wing scales of moths are drawn into the respiratory tract, they can cause mechanical irritation and inflammation of the nasal passages, pharynx, and trachea. Individuals which become sensitized to these insect parts may develop inhalation allergies upon subsequent exposure. Most reported cases involve Hylesia species in South America and the Caribbean region. Thousands of microscopic setae from the lateral and ventral areas at the end of the female abdomen become airborne during outbreaks of these moths. Clouds of setae may be released into the air when the moths are attracted to light at night and bump against windows and outdoor light fixtures. Several such instances involving thousands of human cases of moth dermatitis and inhalation allergies have been reported in Peru (Allard and Allard, 1958) and Brazil (Gusmao et al., 1961).

A less common problem is silk-induced allergies resulting from contact with the silk of certain moths. This most commonly occurs among workers in the silkworm industry. Individuals involved in processing natural silk can become sensitized to silk proteins, leading to skin irritation, conjunctivitis, allergic rhinitis, and asthma. Others may experience similar allergic responses from contact with silk clothing and silk-filled bed quilts, as reported in China (Wen et al., 1990). For further information on inhalant silk allergies, see Kagan (1990).

The major health concern from lachryphagous moths feeding on humans is the irritation of eye tissues caused by microscopic lesions as the tip of the proboscis abrades the eyeball or inner surface of the eyelids. The most discomforting cases are caused by the tarsal claws of species which secure themselves to the eyelids while feeding. Actual damage to the eyes is usually minor, however, and generally heals without becoming infected. The risk of mechanically transmitted agents is greater in the case of ocular abrasions by the tarsal claws than by the proboscis, simply because the tarsi are more apt to become contaminated with infectious agents. They come in contact with a wider array of animal substances and potential pathogens. Nonetheless, there is no evidence that any human pathogen is transmitted by eye-frequenting moths.

The potential for mechanical transmission of pathogens is greatest in the case of skin-piercing moths. The relatively large size of these moths provides a greater surface area for picking up contaminants, while the deeper skin punctures and significant blood flow around the bite wound can be contributing factors. The fact that their bites are more painful than lachryphagous species increases the chances of interrupted feedings and attacks on more than one animal, enhancing prospects for transfer of pathogens. However, there is no documented evidence that any disease agent is transmitted to humans by these moths.

Treatment of urticarial cases includes the mechanical removal of urticating spines or hairs and the application of materials to alleviate the symptoms. The broken spines or hairs can be removed from the skin with fine-tipped forceps or by lightly applying sticky tape to the affected skin surface and lifting the spines or hairs away as the tape is removed. It is important not to rub the spines into the skin in the process of trying to remove them. They also may be removed by submerging the affected areas in warm water to float off the hairs, gently washing the skin surface with running water, or showering. Since components of the venom are generally water-soluble, water helps to dilute and destroy the toxins, thereby reducing their potency.

Other measures taken to relieve discomfort include the local application of ice packs, calamine lotion, and antihistamines. Soaking with warm bicarbonate of soda or solutions of household ammonia is generally ineffective, although relief has been reported in some cases. Mild analgesics such as salicylic acid do not usually provide much relief, either for the localized pain or accompanying headaches.

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