The skin is an essential component of the nonspecific immune system, protecting the host from potential pathogens in the environment. Breaches in this protective barrier thus represent a form of immunocompromise that predisposes the patient to infection. Bites and scratches from animals and humans allow the inoculation of microorganisms past the skin’s protective barrier into deeper, susceptible host tissues.
Thermal burns may cause massive destruction of the integument as well as derangements in humoral and cellular immunity. This enables environmental opportunists and components of the host’s own skin flora to cause infection.
ANIMAL BITES AND SCRATCHES
Each year in In Africa, between 1 and 2 million animal-bite wounds are sustained. The vast majority are inflicted by pet dogs and cats, which number more than 100 million. Other bite wounds are a consequence of encounters with animals in the wild or in occupational settings. While many of these wounds require minimal or no therapy, a significant number result in infection, which may be life-threatening.
The microbiology of bite-wound infections in general reflects the oropharyngeal flora of the biting animal. Although organisms from the soil, the skin of the animal, victim and the animal’s feces may also be involved.
Dogs are responsible for approximately 80 percent of bite wounds, an estimated 15 to 20 percent of which become infected. Most dog bites are provoked and inflicted by the victim’s pet or by a dog known to the victim. These bites frequently occur during efforts to break up a dogfight. Victims tend to be male, and bites most often involve a lower extremity.
Infections typically manifests 8 to 24 h after the bites as pain at the site of injury with cellulitis accompanied by purulent, sometimes foul-smelling discharge. Septic arthritis and osteomyelitis may develop if the canine tooth penetrates synovium or bone. Systemic manifestations such as fever, lymphadenopathy and lymphangitis also may occur.
Common bacteria present on dog bites wounds
Is usually mixed and includes;
- Alpha-hemolytic streptococci,
- Staphylococcus species,
- Pasteurella multocida,
- Eikenella corrodens, and
- Capnocytophaga canimorsus .
- Many wounds also include anaerobic bacteria such as Actinomyces, Fusobacterium, Prevotella, and Porphyromonas species.
While most infections resulting from dog-bites injuries are localized to the area of injury. Many of the microorganisms involved are capable of causing systemic infection.
- Bacteremia/infections of blood,
- Brain abscess,
- Endocarditis and
- Chorioamnionitis in pregnant mothers.
Those bites infections are particularly likely in hosts with edema. Or compromised lymphatic drainage in the involved extremity (e.g., after radical or modified radical mastectomy). And in patients who are immunocompromised by medication or disease. For example, glucocorticoid use, systemic lupus erythematosus, acute leukemia, or hepatic cirrhosis. In addition, dog bites and scratches may result in systemic illnesses such as rabies and tetanus.
Infections with C. canimorsus following dog-bite wounds may result in fulminant sepsis, disseminated intravascular coagulation and renal failure. This is likely to occur particularly in hosts who have impaired hepatic function. Or who have undergone splenectomy or who are immunosuppressed. This organism is a thin gram-negative rod that is difficult to culture on most solid media but grows in a variety of liquid media. The bacteria are occasionally seen within polymorphonuclear leukocytes on Wright-stained smears of peripheral blood from septic patients.
Although less common than dog bites, more than half of all cat bites and scratches result in infections. Because the narrow, sharp feline incisors penetrate deeply into tissue. Cat bites are more likely than dog bites to cause septic arthritis and osteomyelitis. The development of these conditions is particularly likely when punctures are located over or near a joint, especially in the hand. Women sustain cat bites more frequently than do men. These bites most often involve the hands and arms.
Both bites and scratches from cats are prone to infections from organisms in the cat’s oropharynx. P. multocida, a normal component of the feline oral flora, is a small gram-negative coccobacillus implicated in the majority of cat-bite wound infections. Like that of dog-bite wound infections, however, the microflora of cat-bite wound infections is usually mixed.
Other microorganisms causing infection after cat bites are similar to those causing dog-bite wound infections.The same risk factors for systemic infections following dog-bites wounds apply to cat-bite wounds. Pasteurella infections tend to advance rapidly, often within hours. It causes severe inflammation accompanied by purulent drainage. Pasteurella may also be spread by respiratory droplets from animals, resulting in pneumonia or bacteremia. Like dog-bite wounds, cat-bite wounds may result in the transmission of rabies or in the development of tetanus. Infection with Bartonella henselae causes cat-scratch disease and is an important late consequence of cat bites and scratches. Tularemia has also been reported to follow cat bites.
Other Animal Bites
Infections have been attributed to bites from many animal species. Often as a consequence of occupational exposure (farmers, laboratory workers, veterinarians). Or recreational exposure (hunters and trappers, wilderness campers, owners of exotic pets). Generally, the microflora of bite wounds reflects the oral flora of the biting animal. Most members of the cat family, including feral cats, harbor P. multocida. Bite wounds from aquatic animals such as alligators or piranhas may contain Aeromonas hydrophila. Venomous snake bites result in severe inflammatory responses and tissue necrosis, which renders these injuries prone to infection.
The snake’s oral flora
It includes many species of aerobes and anaerobes, such as Pseudomonas aeruginosa, Proteus species, Staphylococcus epidermidis, Bacteroides fragilis, and Clostridium species. Bites from nonhuman primates are highly susceptible to infection with pathogens similar to those isolated from human bites (which are discussed later in this chapter). Also bites from Old World monkeys (Macaca) may result in the transmission of B virus (Herpesvirus simiae, cercopithecine herpesvirus). This is cause of serious infection of the human central nervous system. Seals, walruses, and polar bears bites may cause a chronic suppurative infection known as seal finger, which is probably due to one or more species of Mycoplasma colonizing these animals.
Small rodents, including rats, mice, and gerbils, as well as animals that prey on rodents may transmit Streptobacillus moniliformis (a microaerophilic, pleomorphic gram-negative rod) or Spirillum minor (a spirochete), which cause a clinical illness known as rat-bite fever. The vast majority of cases in the United States are streptobacillary, whereas Spirillum infection occurs mainly in Asia.
In the Africa the risk of rodent bite mainly affects laboratory workers. Or inhabitants of rodent-infested dwellings (particularly children). Rat-bite fever is distinguished from acute bite-wound infection by its typical manifestation after the initial wound has healed. Streptobacillary disease follows an incubation period of 3 to 10 days. Fever, chills, myalgias, headache, and severe migratory arthralgias are usually followed by a maculopapular rash. And characteristically involves the palms and soles and may become confluent or purpuric
Endocarditis, myocarditis, meningitis, pneumonia, and abscesses in many organs. Haverhill fever is an S. moniliformis infection acquired from contaminated milk or drinking water and has similar manifestations. Streptobacillary rat-bite fever was frequently fatal in the preantibiotic era. The differential diagnosis includes Rocky Mountain spotted fever, Lyme disease, leptospirosis, and secondary syphilis. The diagnosis is made by direct observation of the causative organisms in tissue or blood, by culture on enriched media, or by serologic testing with specific agglutinins.
Referred to in Japan as sodoku, it causes pain and purple swelling at the site of the initial bite, with associated lymphangitis and regional lymphadenopathy, after an incubation period of 1 to 4 weeks. The systemic illness includes fever, chills, and headache. The original lesion may eventually progress to an eschar. The infection is diagnosed by direct visualization of the spirochetes in blood or tissue or by animal inoculation.
This distinctive skin infection is caused by direct cutaneous inoculation with Erysipelothrix rhusiopathiae. Because this organism is most often associated with fish and domestic swine, erysipeloid most commonly results from an occupational injury related to fishing (“fish-handler’s disease”) or slaughterhouse work; it may also follow contact with other animals or contact with fish or meat in a household setting. After an incubation period of several days, pain (often severe), edema and a well-demarcated, purplish-red lesion develop. Systemic manifestations are unusual, but bacteremia and endocarditis have occasionally been reported. Definitive diagnosis requires isolation of the bacteria from a biopsy specimen, a tissue aspirate, or blood.
Human Bite Infections
They may be self-inflicted, may be sustained by medical personnel caring for patients, or may take place during fights or domestic abuse or during sexual activity. Also more frequently become infected than do bites inflicted by other animals. These infections reflect the diverse oral microflora of humans, which includes multiple species of aerobic and anaerobic bacteria. Common aerobic isolates include viridans streptococci, Staphylococcus aureus, E. corrodens (which is particularly common in clenched-fist injury; see below), and Haemophilus influenzae.
Anaerobic species, including Fusobacterium nucleatum and Prevotella, Porphyromonas, Peptococcus, and Peptostreptococcus species, are isolated from 50 percent of human-bite wound infections; many of these isolates produce b-lactamases. The oral flora of hospitalized and debilitated patients often includes Enterobacteriaceae in addition to the usual organisms. Human immunodeficiency virus and hepatitis B virus have both been reported to be transmitted by human bite, but these instances appear to be quite rare.
Those are categorized as occlusional injuries, which are inflicted by actual biting. And clenched-fist injuries , which are sustained when the fist of one individual strikes the teeth of another, causing traumatic laceration of the hand. For several reasons, clenched-fist injuries result in particularly serious infections. The deep spaces of the hand, including the bone, joint, and tendons, are frequently inoculated with organisms in the course of such injuries. The clenched position of the fist during injury, followed by extension of the hand, may further promote the introduction of bacteria as contaminated tendons retract beneath the skin’s surface. Moreover, medical attention often is sought only after frank infection develops.
A careful history should be elicited, including the type of biting animal, the type of attack (provoked or unprovoked), and the amount of time elapsed since injury. Local and regional authorities should be contacted to determine whether an individual species could be rabid and/or to locate and observe the biting animal when rabies prophylaxis may be indicated. Suspicious human-bite wounds should provoke careful questioning regarding domestic or child abuse. Details on antibiotic allergies, immunosuppression, splenectomy, liver disease, mastectomy, and immunization history should be obtained.
The wound should be inspected carefully for evidence of infection, including redness, exudate, and foul odor. The type of wound (puncture, laceration, or scratch), the depth of penetration, and the possible involvement of joints, tendons, nerves, and bone should be assessed. It is often useful to include a diagram or photograph of the wound in the medical record. In addition, a general physical examination should be conducted and should include an assessment of vital signs as well as an evaluation for evidence of lymphangitis, lymphadenopathy, dermatologic lesions, and functional limitations.
Injuries to the hand warrant consultation with a hand surgeon for the assessment of tendon, nerve, and muscular damage. Radiographs should be obtained when the bone may have been penetrated or a tooth fragment may be present. Culture and Gram’s staining of all infected wounds are essential. Anaerobic cultures should be undertaken if abscesses, devitalized tissue, or foul-smelling exudate is present. A small-tipped swab may be used to culture deep punctures or small lacerations. It is also reasonable to culture samples from uninfected wounds due to bites inflicted by animals other than dogs and cats. This is because the microorganisms causing disease are less predictable in these cases. A white blood cell count should be determined and blood cultured if systemic infection is suspected.
Wound Management secondary to bites injuries
Wound closure is controversial in bite injuries. Many authorities prefer not to attempt primary closure of wounds that are or may become infected. The preferred mode of management is to irrigate these wounds copiously with saline, debride devitalized tissue, remove foreign bodies. And approximate the wound edges. Delayed primary closure may be undertaken after the risk of infection is over. Small uninfected wounds may be allowed to close by secondary intention. Puncture wounds due to cat bites should be left unsutured because of the high rate at which they become infected. Facial wounds are usually sutured after thorough cleaning and irrigation because of the importance of a good cosmetic result in this area and because anatomic factors such as an excellent blood supply and the absence of dependent edema lessen the risk of infection.
Antibiotics should be administered in all established bites-wound infections. They should be chosen in light of the most likely potential pathogens. This usually indicated by the biting species and by Gram’s stain and culture results. For dog and cat bites, antibiotics should be effective against S. aureus, P. multocida, C. canimorsus, streptococci, and oral anaerobes. For human bites, agents with activity against S. aureus, H. influenzae, and b-lactamase-positive oral anaerobes should be used.
Broad spectrum antibiotics
The combination of an extended-spectrum penicillin with a b-lactamase inhibitor (amoxicillin/clavulanic acid, ticarcillin/clavulanic acid, ampicillin/sulbactam).Those appears to offer the most reliable coverage for these pathogens. Second-generation cephalosporins (cefuroxime, cefoxitin) also offer substantial coverage. The choice of antibiotics in penicillin-allergic patients (particularly those in whom immediate-type hypersensitivity makes the use of cephalosporins hazardous) is more difficult and is based primarily on in vitro sensitivity since data on clinical efficacy are inadequate. The combination of an antibiotic active against gram-positive cocci and anaerobes (such as clindamycin) with trimethoprim-sulfamethoxazole. Or a fluoroquinolone which has activity against many of the other potential pathogens, would appear reasonable.
Antibiotics are normally given for 10 to 14 days, but the response to therapy must be carefully monitored. Failure to respond should prompt a consideration of diagnostic alternatives and surgical evaluation for possible drainage or debridement. Complications such as osteomyelitis or septic arthritis mandate a longer duration of therapy.
Management of C. canimorsus sepsis requires a 2-week course of intravenous penicillin G (2 million units intravenously every 6 h) and supportive measures. Alternative agents for the treatment of C. canimorsus infection include cephalosporins and fluoroquinolones. Serious infection with P. multocida (e.g., pneumonia, sepsis, or meningitis) should also be treated with intravenous penicillin G. Alternative agents include second- or third-generation cephalosporins or ciprofloxacin.
Venomous snake bites
Bites by venomous snakes may not require antibiotic treatment, but it is often difficult to distinguish signs of infection from tissue damage caused by the envenomation. Thus many authorities continue to recommend treatment directed against the snake’s oral flora¾i.e. the administration of broadly active agents such as ceftriaxone (1 to 2 g intravenously every 12 to 24 hours) or ampicillin/sulbactam (1.5 to 3.0 g intravenously every 6 hours).
Seal finger appears to respond to doxycycline (100 mg twice daily). E. rhusiopathiae is sensitive to most b-lactam antibiotics, including penicillin, as well as to ciprofloxacin. Its resistance to vancomycin, which is unusual among gram-positive bacteria, is of potential clinical significance since this agent is sometimes used in empirical therapy for skin infection.
The use of antibiotics in patients presenting early after bite injury (within 8 hours) is controversial. Although symptomatic infection will not yet be manifest in many of these wounds at this point, many early wounds will harbor pathogens, and many will become infected. Studies of the use of prophylactic antibiotics in wound infections are limited. And have often included small numbers of cases in which various types of wounds have been managed according to various protocols.
A recent meta-analysis of eight randomized trials of prophylactic antibiotics in patients with dog-bite wounds demonstrated a reduction of the rate of infection by approximately 50 percent with prophylaxis. However, in the absence of sound clinical trials, many clinicians base the decision to treat bite wounds presumptively with empirical antibiotics on the species of the biting animal. That is, the location, severity, and extent of the bite wound. And the existence of comorbid conditions in the host.
Human and Monkey bites wounds
All human- and monkey-bite wounds should be treated presumptively because of the high rate of infection. Most cat-bite wounds, particularly those involving the hand, should be treated. Other factors favoring treatment for bite wounds include severe injury, as in crush wounds; potential bone or joint involvement; involvement of the hands or genital region; host immunocompromise, including that due to liver disease or splenectomy; and prior mastectomy on the side of an involved upper extremity. When prophylactic antibiotics are administered, they are usually given for 3 to 5 days.
It consisting of both passive administration of rabies immune globulin and active immunization with the human diploid vaccine. This should be given in consultation with local and regional public health authorities for many wild-animal (and some domestic-animal) bites and scratches as well as for certain non bite exposures. Rabies is endemic in a variety of animals, including dogs and cats in many areas of the world. Many local health authorities require the reporting of all animal bites.
A tetanus booster immunization
It should be given if the patient has undergone primary immunization but has not received a booster dose in the past 5 years. Patients who have not previously undergone primary immunization should be immunized and should also receive tetanus immune globulin. Elevation of the site of injury is an important adjunct to antimicrobial therapy. Immobilization of the infected area, especially the hand, is also beneficial.