The risk of HIV transmission following a bite injury is important to many groups. The first are those who are likely to be bitten as an occupational risk, such as police officers and institutional staff.  Another group are represented by the victims and perpetrators of crimes involving biting – both in attack and defense situations.  The possibility of these bites transmitting a potentially fatal disease is of interest to the physicians who treat such patients and the legal system who may have to deal with the repercussions of such a transmission.  Bite injuries represent one percent of all emergency room admissions in the US and human bites are the third most common following dogs and cats.  The world-wide epidemic of HIV & AIDS continues, with over five million new cases last year and 1 in 100 sexually active seropositive adults.  A review of the literature concerning human bites, HIV and AIDS, HIV in saliva and case examples was performed to examine the current opinion regarding the transmission of HIV via this route.  In conclusion, a bite from an HIV seropositive individual, which breaks the skin or is associated with a previous injury, carries a risk of infection for the bitten individual. 

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Introduction

The transmission of the human immunodeficiency virus via human bite is important to a number of distinct groups.  The first group are those who are likely to be bitten as an occupational risk, such as police officers, correctional officers, medical personnel and others working in an institutional setting.  Another group are represented by the victims and perpetrators of crimes involving biting – both in attack and defense situations.  The possibility of these bites transmitting a potentially fatal disease is of interest to the physicians who treat such patients and the legal system who may have to deal with the repercussions of such a transmission.  A bite injury which transmitted HIV to the recipient could be classed as assault with a deadly weapon. Other diseases have been transmitted by biting such as syphilis (1) and hepatitis B  (2-4).  Case examples do exist which demonstrate the potential for HIV to be transmitted via a bite. 

This paper attempts to examine the potential transmission risk by analyzing the incidence and nature of bites, the prevalence of HIV and AIDS, the occurrence of HIV in the oral cavity (saliva and blood) and by the examination of case reports of HIV transmission via human bites.  

Methods

A literature review was performed to investigate the current opinion on the subject of HIV and AIDS transmission with an emphasis on bites.  Key search words used were “Human Bites”, “HIV”, “AIDS”, “HIV Transmission”, “Saliva”, “HIV Risk”.  The search utilized Medline (1966 – present), AidsLine and Current Contents using the Ovid search engine.  Other resources included the Center for Disease Control and Prevention and the World Health Organization databases.  

Prevalence of bites

The biting of one human by another is the third most common bite injury following dogs and cats (5) and was first reported in the literature by Hultzen in 1910 (6) who described an infective sequel to a human bite.  About one half of the people in America will be bitten by an animal or human during their life time and these injuries will account for 1% of all emergency room admissions and cost over 25 million dollars in health care expenses per year (5).

In addition to these statistics not all cases are reported to a public health agency.  One study reported the incidence of human bite injuries in New York City to be 11. 8/100,000 people per year (7).  Other studies found that the incidence in children is close to one human bite per 600 pediatric emergency room visits (8,9).

Bites have been described to occur in a number of situations, including overtly aggressive behavior (violent & sexual attacks), accidental bites (e. g.  those associated with sports and medical treatment) and sexual activity (7). The site of a bite is an important variable in the risk of infection.  Male victims of bites are most frequently bitten on the hand, arm and shoulder; female victims are most frequently bitten on the breast, genitalia, leg or arm (10). The distribution of bites are:- for hand and upper extremities 60-75%, for head or neck 15-20%, for trunk 10-20%, for lower extremities 5% and for other sites 5-10% (11,12) See fig I. When analyzing these figures on bite frequency and site, it is important to remember that there is a bias introduced by the fact that the figures relate only to those individuals who sought treatment (14,15).  Failure to attend could be motivated by the severity of the injury, inadequate self-treatment or if the individual was attacked as part of a violent crime.  Many individuals do not seek treatment for human bites due to embarrassment and legal repercussions (16,17).

 The reported infection rate of human bites varies.  The infection rate for a bite to the hand was 28%, in one study, compared to only 4% for bites to the facial area (18).  Mann and co-workers examined fifty human bites and found a 50% incidence of infection (19).  In another study an infection rate of 17. 7% of 434 bites was reported (15).  Despite these variations it should be noted that human bites have a higher incidence of infection than any other bite type such as dog or cat (20), but the potential for bias as previously discussed must also be considered (14,15)

The hand, of all potential bite sites, is the most likely to have an infective sequel, especially if the injury involves the metcarpophalangeal (MCP) joint (19).   This kind of injury is most likely to occur in a “clenched fist” situation.  This typically occurs when the attacker strikes and hits the victim in the mouth and causes a laceration from the teeth. In the clenched fist injury, a laceration of roughly 5mm occurs, typically in the third MCP joint (normally the most prominent), which looks superficial and benign (17).  Typically the patient will extend their hand to examine the injury and in the process create a deep inoculum of oral bacteria that enter the wound (19).  Some authors believe that a clenched fist injury is a separate entity to a bite mark (21) and that the two should be separated in bite classifications.

 Nature of Bites

 Bites can be described in an ascending scale of severity, beginning with petechial hemorrhage (errythema), contusion (ecchymosis), abrasion, laceration (incision), and ending with avulsion. The severity of the bite injury is one factor that is likely to increase the chance of HIV transmission.  HIV is a predominately blood transmitted virus (22,23) so, in order to access the victims blood, a bite must at least break the skin - hence an abrasion or more severe injury.  Consideration must also be given to skin that is already broken.  For example, skin with a previous injury or pathological lesion that suffers a superficial bite may allow saliva or oral blood to contact the bite recipients’ blood. 

 Prevalence of HIV

The first reports of AIDS were published in 1981 (24).  These reports described a cellular immunodeficiency with no identifiable cause.  This deficiency caused the development of a variety of opportunistic infections and malignancies – many of which were extremely rare.  Later the cause of the syndrome was found to be a retrovirus (HTLV-III) which is now known as the human immunodeficiency virus (HIV-1) (24).

The incidence of HIV continues to spread around the world, with the World Health Organization quoting 5. 8 million individuals newly infected in 1997 (25).  The report also cites that one in a hundred sexually active individuals, worldwide, are HIV positive (the sexually active age bracket is given as 15-49).  Many of these individuals are unaware of their status and are therefore unable to take precautions to prevent further spread (25). Of importance, considering the biting habits of children (8,9), is the prevalence of  HIV and AIDS in children.  These children are normally infected during pregnancy or via breastfeeding from their HIV positive mothers, many of whom are intra-venous drug abusers.  The WHO report cites that currently 1. 1 million children are living with HIV / AIDS (25).  

The overall extent of the problem can be best demonstrated by the figures of 16,000 new infections per day, with the total number of infected individuals in the world today being 30. 6 million (25).  Table I shows the relative occurrence in North America and the United Kingdom.  

HIV and saliva

The presence of HIV in saliva has been examined by many investigators (29-32, 35-37).  The results in table II show the efforts of two different studies.  Results of Groopman et al. suggested a decline in the relative HIV presence in saliva as the disease progresses (33).  Ho was unable to detect the presence of HIV in patient's saliva until the patient was in the terminal stages of the illness, demonstrating an apparent contradiction of Groopman's earlier results (34).  There are no indications whether or not the saliva was contaminated by blood in either studies (29).  The decreasing viral load, with increasing disease progression, is explained by the reduction in the number of immune products available, and hence the number of antibodies available for test diagnosis.  In 1986, Archibald (30) (working with Groopman) found that 70% of AIDS patients and 93% of patients with AIDS-related complexes had salivary antibodies to HTLV-III cells - these results are in line with that of Groopman’s earlier work. Following this work in 1993, Yeung revisited the problem and the results of this study are shown in Table III (29,38), with HIV isolated from 21% of the saliva samples versus 86% of the blood samples, even in the presence of periodontal disease, a source of oral blood.

 The oral cavity may contain blood, and saliva can become contaminated with this blood.  Piazza and co-workers suggested that blood is present in 50% of healthy subjects with no visible oral lesions (31), although they recommended that the presence of  blood would indirectly indicate the presence of  such microlesions (32).  After activities such as teeth brushing, eating, or passionate kissing the blood quantity in saliva increases significantly (32).  It is also true that many dental procedures such as supra & subgingival scaling, cavity preparations and impressions are likely to produce the same increase in salivary blood load.  

As an adjunct to these studies, researchers discovered the presence of retrovirus like particles from major salivary glands, another possible indication of the likelihood of saliva containing HIV (35). Investigators have explained the low viral detection from saliva in terms of the presence of HIV inhibiting factors.  A federal update from the CDC, published in the JAOA states that “Saliva inhibits HIV-1 infectivity” (36).  The work of McNeely et al. (37) came to the conclusion that a protein in saliva (SLPI) had significant anti-retroviral activity and that this may be important in the low transmission rate of HIV via the oral route. In two studies Archibald & Zon (30,39) suggest that specific IgA antibody exists in saliva to HIV.  In those individuals who are IgA deficient then HIV may be more transmissible via the salivary route (39).  Later work confirmed this anti-HIV effect (40), with the conclusion that there are several mechanisms at work inhibiting HIV in saliva.  

Shine et al. (41), in their comprehensive review of the subject warn that, despite ample evidence for anti-HIV factors in saliva, the extent to which they operate in vivo is unknown and the subject merits further investigation. These studies show that the viral quantity in saliva is low or is supplemented by the presence of blood contamination.  The source of this blood may be from undetectable microlesions, trauma or periodontal disease.  The saliva may not appear blood stained on visual inspection but can still contain blood. In addition to these factors, several oral diseases are associated with AIDS and HIV.  These include acute ulcerative gingivitis and periodontitis (ANUG, ANUP), Kaposis’ sarcoma and hairy leukoplakia.  These oral conditions are likely to cause intra-oral bleeding, and hence the risk of infection from those individuals demonstrating these conditions is likely to be increased. Considering the oral cavity as potentially containing HIV - whether from blood or saliva sources allows a simpler analysis of the transmission risk.  We should give notice to warnings such as those issued by Shine et al. and avoid complacency where doubt still exists (41).

Case Examples 

The following examples describe incidences of persons being bitten by HIV positive individuals.  The conclusions of the authors are presented and discussed.  

Case One (42).

A 26 year-old health care worker presented for an HIV test and the results were found to be positive.  The woman claimed to have never injected drugs, had no blood transfusion history, no recent travel abroad or needlestick injury.  She reported having three sexual partners, two tested negative for HIV antibodies and the third was an untraceable “one-night-stand” and could not be tested. The woman who presented for testing had reported being in a fight with her sister.  During this fight the woman had knocked some of her sisters teeth out, causing an intraoral bleed.  Later in the fight the sister bit the woman on the leg - the woman reports that her sister’s mouth was still bleeding at this time.  The Lancet report did not provide information about the severity of the bite. The sister was a long-term intravenous drug user and had been diagnosed HIV seropositive prior to the fight.  The authors of the case report stated, “ Since the risk of HIV transmission from a single sexual encounter is probably low, the most likely route of infection in this case is the bite” (42). In this case, the third sexual partner was not found and thus not tested.  This raises uncertainty about the route of transmission.  The conclusion is drawn from the attack from a known positive individual versus a sexual encounter from an individual with unknown status.  

Case Two (43).

This case describes a 47-year-old homosexual man suffering from AIDS who transmitted HIV to his neighbor.  The sequence of events described begins with the individual suffering a grand mal seizure at home.  Frightened, the individual went to his neighbor's home for assistance where he experienced another seizure.  In an attempt to clear the man’s airway during this second seizure, the neighbor was bitten.  The bite resulted in a small crack and shallow wound on his left index finger-nail.  This wound was not visibly bleeding. Following the incident, the neighbor noticed blood in the biter’s saliva and washed his hands approximately half an hour following the bite.  An hour after the bite a physician examined the wound on the bitten man.  A bite wound was noticed on the biter’s tongue at a later examination. Blood samples were taken from the bitten man and tested for HIV and were found seronegative.  He was given a prophylactic treatment of 1200 mg per day Zidovudine – an anti-retroviral drug.  Despite these efforts, he had completely seroconverted by the 54th day following the bite.  The biter died 13 days after the incident. The bitten man had been married for 23 years and his wife tested consistently negative for HIV-1.  The individual claimed to have no additional sexual partners, blood transfusions, surgical operations, or invasive procedures.  There was no evidence of hepatitis B infection, and he had never traveled to countries with a high incidence of HIV infection.  The bitten man reported that his only previous encounters with the biter were occasional social contacts and that he never came into contact with any body fluids. The authors of this case report concluded that the likely source of the HIV in this bite was the blood from the bitten tongue.   Of interest in this case is the apparent superficial nature of the bite.  

Case Three (44).  

A six-year-old boy was bitten by his younger brother.  The younger brother had transfusion acquired AIDS.  When examined 6 months following the bite the older brother was found to have seroconverted. In this bite, there was no reported exchange of blood, nor did the bite break the skin.  This report describes that the younger brother also suffered some of the neurological complications of AIDS.  This has led to speculation that the sibling's seroconversion could have occurred during other interactions and not the result of the bite.  

Case Four (45).  

A healthy 28-year-old woman was employed as a cashier in a grocery store.  On March 28, 1985 she responded to a call for help from the rear of the store, where she found a man lying on the floor in a seizure and, in order to prevent airway obstruction, she placed her fingers in the man’s mouth.  The man’s jaw jerked shut and she was bitten deeply on the dorsal aspect of the proximal phalanx of the index finger.  The authors’ of the letter report that the wound bled profusely, but there was no need for a suture closure. It was learned later that the biter was seropositive for HIV.  The biter died in November of the same year as the incident.  The bitten patient was reported as receiving no immunoprophylaxis injections, which is in contrast to case two. The woman has undergone monthly physical examinations and blood screenings following the accident.  There are no signs of lymphadenopathy nor has she seroconverted - 18 months after the incident the women is still seronegative (45). This case raises issues regarding the likely time of seroconversion following a bite.  In the previous cases times ranged from 57 days to 24 months.  It is thought that the seroconversion occurs at around two months when transferred via the blood-blood route (which a bite may represent) (46-48).  When examining the sexual transmission route Ranki et al offers evidence for a seroconversion time of 18 months (52). When studying seroconversion times and bite injuries, questions arise as to the source of the HIV.  If it is restricted to blood in saliva can we regard a bite injury as blood-blood transmission? – this time scale would explain the rapid conversion described in case two.  On the other hand, if saliva is the transmission agent, then will the seroconversion times be longer? This information is not currently available – but is essential for both bitten individuals and their treating physicians.  The question “Following a potentially infected bite how long should we test for HIV?” cannot be answered at present.

 Case Five (49).

 In this article, the authors studied the results from 74 hospitals involved in the “Exposure Prevention Information Network (EPINet)” program.  In this system hospitals send details of any employees’ occupational percutaneous injuries, exposures to blood or body fluids to researchers at the University of Virginia. Tereskerz et al. looked at these figures to determine the rate of bite exposures and the association of risk factors that might increase the occupational infection risk (49).  50 of the 10,125 incidents involved a bite with an annual rate of 0. 12 bites per 100 occupied hospital beds.  The details of these bites are described in Table 4 The authors extrapolated from these figures that with 518,400 occupied US hospital beds then an annual total of 622 reported bites could be anticipated.  The hospitals involved reported that 1.7% of the described exposures involved an individual who was HIV positive.  None of the bites described in the study were known to result in the transmission of HIV or AIDS. There are data concerning blood in the biters’ mouth available for some of these bites.  The authors report data available for 36 of the 50 bites.  Within these 36 bites, blood was noted in three cases but in none of these cases was there a break in the integrity of the skin.  In 28 of the bites there is a description of the bites.  Interestingly, none were accidental or involuntary bites as in cases 2 & 4.  The distribution is shown in Figure II. Although none of the bites resulted in a known transmission of HIV, the authors concluded that the fact that the hands and arms suffered 86% of the bites is an indication for consistent glove use and arm protection.  This protection is especially important when in close contact with combative, pediatric or psychiatric patients (49).  

Case 6 (50)

In this article the investigators examined a household in which an HIV positive toddler (36 months old) began biting his family.  The child had contracted HIV from his mother who had a history of I.V. drug abuse.  The child lived with his mother until she died, and then moved to live with his extended family, which comprised of three adults and four cousins with a fifth visiting regularly.  None of these individuals were reported as having any risk factors for HIV. At the age of three he began to bite his relatives and the authors describe that over a two week period four cousins were bitten.  None of these bites broke the skin.  A fifth cousin with an impetiginous lesion shared his bed with the HIV positive toddler and was exposed to his urine due to the toddlers nocturnal enuresis.  After these bites, the child was confined to the household and adult supervision maintained.  By using positive reinforcement, the biting behavior ceased. The investigators analyzed each of the five cousins for seroconversion immediately after the exposure (bite or urine) and then at 3, 6, 12 and 20 months.  They found that all cousins remained physically healthy with no detection of HIV antibodies.  The authors state that they continue to support the Center for Disease Control guidelines regarding unrestricted school attendance for HIV-infected children who can control their bodily secretions and do not exhibit any aggressive behavior, such as biting (51).  It can be extrapolated from this conclusion that those HIV positive toddlers with uncontrolled behavior should not be allowed unrestricted school attendance.  

Conclusions

It is possible for a bite from an HIV infected individual to transmit the human immunodeficiency  virus.  The likely risk of transmission will be increased if :- 

* Blood is present in the oral cavity

* Larger amounts of blood in the mouth carry a larger risk

* The bite breaks the skin

* The bite is associated with a previous injury

            * The biter has a deficiency of anti-HIV salivary elements – e. g.  is IgA deficient

 Recommendations 

If an individual is bitten, treatment should be sought immediately and a risk analysis performed.  The use of prophylactic anti-retrovirals may be appropriate in such situations.  Health care workers, care givers, police officers and others at risk of bites should be aware of this potential transmission route and take preventative measures such as hand and arm protection.  

In order to increase our understanding of this transmission route and to reach more satisfactory conclusions, the availability of incidence studies is essential.  No review can make up for the lack of such data and the availability of well described case reports.  Nevertheless it can be concluded that HIV and biting is a potential transmission mode for HIV.  Those persons at risk of bite injuries should be informed of this transmission route.  

Acknowledgments 

The authors would like to thank Ms. Juliana J. Kim and Dr. Dean P. Hildebrand for their assistance in reviewing and editing this article.

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Figure 1

Figure 2

 Table 1

“Persons” includes adults & children

Data from (26) (UK), (United States) (27), (Canada) (28)

 Table 2

Healthy : HIV seropositive but asymptomatic patients

ARC : patients with AIDS-related complexes as defined by CDC

 Table 3 

Asymptomatic : HIV seropositive but asymptomatic patients

PGL : persistent generalized lymphadenopathy

ARC : AIDS related complex

AIDS : Acquired Immune Deficiency Syndrome

  Table 4