Hookworms - Clinical Pathology PDF

CLINICAL PATHOLOGY I – Lecture Hookworms I. Classifications and taxonomic species of importance A. Classified as a nematode B. In the family Strongylidea 1. Strongyles is from the Greek strongulos, meaning round C....

CLINICAL PATHOLOGY I – Lecture Hookworms I. Classifications and taxonomic species of importance A. Classified as a nematode B. In the family Strongylidea 1. Strongyles is from the Greek strongulos, meaning round C. Derives the common name hookworm by how the head bends dorsally D. Species of importance 1. Ancylostoma caninum a. Most common hookworm of dog b. Sometimes (rarely) called “southern” hookworm c. Also found in  Fox  Coyote  Wolf  Raccoon  Badger d. By far most pathogenic e. ZOONOTIC 2. Ancylostoma tubaeforme a. Most common hookworm of domestic cats b. And other wild Felidae c. ZOONOTIC 3. Ancylostoma braziliense a. Yet another hookworm, capable of infesting both dogs and cats b. ZOONOTIC 4. Uncinaria stenocephala a. Aka “northern” hookworm b. Found in dogs in Northern US and Canada c. Can be found in cats, though rarely d. Also found in  Fox  Coyote  Wolf e. Not as pathogenic as Ancylostoma spp. f. NOT zoonotic 5. Necator americanus & Ancylostoma duodenale a. The human hookworms 12/3/2024 1  II. General Information A. Life cycle is direct (just like ascarids), but can utilize indirect transmission via PH (just like ascarids) B. Transmitted in various ways (similar to ascarids) C. Undergo various migrations (similar to ascarids) D. Adults located in small intestine of definitive host (just like ascarids) E. Description of Hookworms 1. Adults are creamy white 2. Males about one-half inch long 3. Females about one-half to two-thirds inch long 4. Adults have cutting plates or teeth that enable them to suck blood -- LOTS of blood 5. Anterior end of adult parasite is bent in a dorsal direction giving “hook” appearance F. “Hookworm” ova 1. Typical “strongyle-type” egg; i.e., several cells within ovum  In small animals, called “hookworms”  In ruminants, similar endoparasites called “trichostrongyles”  In horses, similar endoparasites called “strongyles” G. Direct Life Cycle 1. Ova pass in feces, initiating larval development 2. 1st stage larvae hatch from ova; 2nd and 3rd stage larvae develop in soil, living on bacteria and debris 3. 3 stage (“L3”) is the infective stage: Takes 2 to 9 days depending on environmental rd conditions H. Larvae Facts of Life 1. All larval stages highly susceptible to drying and freezing 2. Larvae require lots of rainfall (~ 50 inches per year) – cannot withstand desiccation 3. Larvae prefer warm temperatures, but can survive some degree of cold weather 4. Once infective, larvae typically transmitted through oral ingestion or skin penetration 5. Larvae can live weeks to months as free-living organisms III. Transmissions: All involve 3rd stage larvae (“L3”), the infective stage. A. Oral ingestion: Prepatent period ~ 2 weeks B. Skin penetration: Prepatent period ~ 4 weeks C. Transplacental: Prepatent period ~ 4 weeks. Occurs only in puppies (and is much less common than transmammary transmission). D. Transmammary: Prepatent period ~ 2 weeks. Occurs only in puppies (and is the more common route of transmission to neonates). E. Paratenic host: Prepatent period ~ 2 weeks 12/3/2024 2 IV. Migrations  Mucosal  Tracheal  Somatic A. Mucosal Migration 1. Occurs following oral ingestion of infective larvae (from environment, from milk, from paratenic host), and is only migration necessary for parasite to complete maturation  Swallowed larvae penetrate mucosa of small intestine  Develop to 4th stage  Attach to intestinal wall lining and begin to suck blood  Develop to mature stage 2. Prepatent period: ~ 2 weeks B. Tracheal Migration 1. Occurs following skin penetration of infective larvae (including transplacental transmission) in animals < 3 months of age  Larvae penetrate skin and migrate through tissues to venule  Larvae carried via circulatory system to heart and finally to lungs  Move up trachea and swallowed to small intestine where develop to maturity (following mucosal migration) 2. Prepatent period: ~ 4 weeks C. Somatic Migration 1. Occurs following skin penetration of infective larvae in animals > 3 months of age a. Begins like tracheal migration, but larvae encyst in tissues of adult and do not complete lifecycle unless... b. Larvae are re-activated with pregnancy, enter dam’s circulation and travel to  Placenta then fetal liver (rarely in dogs)  Mammary glands and enter milk (commonly in dogs) 2. This migration provides larvae for both transplacental and transmammary transmission 3. During pregnancy or at birth  Transplacental transmission: Larvae leave liver and travel through venous circulation to heart, lungs, etc. and complete tracheal migration to establish patent infestation (less common route of transmission to puppies)  Transmammary transmission: Larvae are ingested via milk, undergo mucosal migration and establish patent infestation (more common route of transmission to puppies) 4. Prepatent periods in the neonate  Transplacental transmission: ~ 4 weeks  Transmammary transmission: ~ 2 weeks 12/3/2024 3  5. Encysted larvae can become “reactivated” after removal of adult hookworms from intestine by way of deworming. This is called “larval leak”.  Very difficult to “clear” an adult of hookworms  However, animals develop some immunity to hookworms as they age V. Pathogenesis & Clinical Signs: Three phases  Skin penetration  Tracheal migration  Intestinal infestation A. Clinical Signs of Skin Penetration 1. Marked itching (pruritus) and redness (erythema), along with papular eruptions, especially in interdigital areas and legs 2. May develop secondary bacterial infection B. Clinical Signs of Tracheal Migration 1. Typically subclinical 2. Lesions primarily result in hemorrhage in alveoli, and may be significant in heavy infestations 3. Hemoptysis may be observed C. Clinical Signs of Intestinal Infestation 1. Blood loss is responsible for most illness and death of hookworm patients 2. Marked bloodsucking leads to debilitating ANEMIA  Begins as anemia due to low numbers of RBCs; i.e., normocytic, normochromic  Progresses to anemia of low hemoglobin (Hb); i.e., microcytic, hypochromic 3. Severity depends on age along with nutritional and health status of animal  Severe infestations result in severe anemia, dark, tarry diarrhea, emaciation, and if untreated may lead to death  Chronic disease may cause anorexia, low body weight, and weakness VI. Diagnosis A. Fecal flotation 1. Number of eggs present does not indicate severity of infestation 2. In neonate, presence of any hookworm ova should be considered serious 3. It is possible, especially in neonatal infestations, to have serious disease without presence of ova; i.e., incubation period is shorter than prepatent period VII. Drugs and Treatment Regimen A. Anthelmentics for Dogs o Pyrantel pamoate PO o Fenbendazole PO o Milbemycin oxime PO o Moxidectin SQ or topical B. Anthelmentics for Cats 12/3/2024 4  o Pyrantel pamoate PO o Fenbendazole: PO o Milbemycin oxime PO o Moxidectin Topical o Ivermectin PO o Selamectin Topical o Emodepside Topical C. Treatment Regimen for Adults 1. Administer appropriate anthelmintic and provide good plane of nutrition 2. Adults DO acquire immunity to hookworms as they age D. Treatment Regimen for Neonate 1. Tx immediately with appropriate anthelmintic at 2, 4, 6 and 8 weeks of age 2. Provide supportive care: High protein diet, iron, and vitamin supplements 3. May require blood transfusion VIII. Environmental Control of Hookworms A. Especially important for feline and canine breeding operations 1. Hygiene -- remove feces 2. Larval stages penetrate skin very easily, all outside runs and pens should be cleaned thoroughly and regularly B. Products that will kill larvae  Sodium borate: 10 pounds per 100 square feet of surface for soil (place on ground, rake over, and water)  Bleach: 1% solution for kennels C. Prevention of Hookworms 1. Routine sanitation including prompt removal of feces 2. Periodic anthelmintic testing and/or treatment of adult animals 3. Keep cats indoors and dogs on leash or fenced 4. Enforce leash laws; require owners to remove feces from public areas 5. Bitches can be treated from day 40 of gestation to day 14 of lactation with fenbendazole or high doses of ivermectin IX. Public Health Significance A. Cutaneous Larva Migrans (CLM): Aka “creeping eruption” 1. Dog and cat hookworm larvae can penetrate skin of humans (occurs most often in coastal areas) 2. Signs include intense pruritus, followed by erythema and edema, eventually resulting in vesicular eruptions 3. Does not develop a patent infestation in humans unless hookworm is human hookworm (i.e., A. duodenale or N. americanus) 4. Itching starts about 1 hour after larval penetration 5. Intense itching lasts about 1 week 6. Scratching can lead to secondary bacterial infection 7. In extreme cases, larvae can leave tunnels under skin that look similar to varicose veins 8. Treatment in affected people is thiabendazole (topical and/or oral) 12/3/2024 5 12/3/2024 6