Kaohsiung J Med Sci October 2007 • Vol 23 • No 10 511
Venomous snakes have been held responsible for more deaths than all other venomous and poisonous animals added together. They exist in a wide range of habitats throughout the world, with the exception of Antarctica. The majority of snake bites are caused by non-venomous snakes, and in clinical findings, very few cases of venomous snake bites appear. Despite this,
estimates suggest that there are more than 2.5 million venomous snake bites annually, resulting in more than 125,000 deaths. Snake bite is also one of the major causes of morbidity and mortality in developing coun-tries, with the risk being highest among the local popu-lations of rural tropical areas. Venom injected into local tissue causes local and systemic reactions. Clinical findings may vary according to the species and age of the snake, the depth of the bite, the amount of injected venom, and the age, gender and general health status of the victim. The purpose of the present study was to analyze data on snake bites in southern Taiwan, in order to consider the problems created by venomous snakes in tropical countries.
Received: February 26, 2007 Accepted: May 3, 2007 Address correspondence and reprint requests to: Dr Chung-Sheng Lai, Division of Plastic and Reconstructive Surgery, Kaohsiung Medical University Hospital, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan.
E-mail: kapich@kmu.edu.tw
M
ANAGEMENT OF
P
OISONOUS
S
NAKE
B
ITES IN
S
OUTHERN
T
AIWAN
Kao-Ping Chang,1,2Chung-Sheng Lai,1,2and Sin-Daw Lin1,2
1Faculty of Medicine, College of Medicine, Kaohsiung Medical University, and 2Division of Plastic and Reconstructive Surgery, Department of Surgery,
Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.
Snake bite envenomation is not uncommon in Taiwan. This study focuses on the pattern of poison-ous snake bites and their management in southern Taiwan over a 5-year period. The case histo-ries of 37 patients with poisonous snake bites admitted to the Kaohsiung Medical University Hospital between June 2001 and July 2005 were analyzed retrospectively. Three patients, bitten by unknown species of venomous snakes, were excluded from this study. The frequency of snake bites from each species of snake, the local and systemic manifestations of snake bite, treatment of complications and final outcomes were analyzed. Of the remaining 34 patients, 11 (32.4%) were bitten by bamboo vipers, 10 (29.4%) by Russell’s pit vipers, 8 (23.5%) by Taiwan cobras and 5 (14.7%) by Taiwan Habu. The majority of snake bites (28) occurred between May and November. Those affected were mainly outdoor hikers (14) and workers (9). The antivenin requirements for treatment in the emergency room were in accordance with standard procedures. No mortality was noted among those envenomed by poisonous snakes. Although poisonous snake bite is not a common life-threatening emergency in the study area, we observed both an environmental risk and a sea-sonal incidence of snake bite. Keeping the varied clinical manifestations of snake bite in mind is important for effective management. Ready availability and appropriate use of antivenin, close monitoring of patients, institution of ventilatory support and early referral to a larger hospital when required, all help reduce mortality.
Key Words:acute renal failure, envenomation, snake bite (Kaohsiung J Med Sci 2007;23:511–8)
M
ATERIALS ANDM
ETHODSA total of 37 patients with histories of snake bite were admitted to Kaohsiung Medical University Hospital between June 2001 and July 2005. Data from chart records were summarized in this retrospective series. This study evaluated factors concerning the severity of skin necrosis in local bite sites and systemic symp-toms resulting from venomous toxins among snake bite patients in southern Taiwan. We studied 37 vic-tims retrospectively. Three were excluded because they had been bitten by unknown species of snakes. Data collected from the remaining 34 patients included: gender, anatomic location of the bite, where the attacks took place, and predisposing factors that might have affected the clinical course. Renal function studies included measurement of serum urea nitrogen and serum creatinine concentrations. Hematologic studies consisted of bleeding time, partial thromboplastin time, platelet count, plasma fibrinogen and fibrin degrada-tion products, and urinary hemoglobin. Patients were treated either conservatively or aggressively by dialy-sis and intubation. All 34 were treated with antibiotics, and received standard antivenin treatment, which is discussed later in the article.
R
ESULTSMost patients were asymptomatic or mildly symptom-atic, except for local skin lesions. Of the 34 patients, 11 (32.4%) were bitten by bamboo vipers, 10 (29.4%) by Russell’s pit vipers, eight (23.5%) by Taiwan cobras and five (14.7%) by Taiwan Habu. The majority of snake bites (29) occurred between April and September, with the peak in June (10), which is the early part of the rainy season in Taiwan (Figure 1). The majority
of snake bite victims were males (73.5%), with an age range of 20 to 71 years. However, there were two children (5.9%) under 10 years of age in our series. Most bites were on the toes and fingers (44%), with bites on the lower and upper limbs representing 38.2% and 14.7% of bites, respectively. Interestingly, one child suffered a snake bite on the upper lip while playing.
Most bites occurred in rural areas, outdoors, and in dark places. Those affected were mainly outdoor hikers (14) and outdoor workers (9). Times between being bitten and arrival at our hospital ranged from 30 minutes to 30 hours. The amount of time that elapsed between being bitten and hospitalization did not result in significant differences in whether or not patients had severe tissue necrosis. Only one patient was treated first with an unknown traditional regimen (Chinese herbal or folk medicine treatment) before undergoing medical therapy. The antivenins used in all patients were in accordance with the standard protocols for each species. Hospitalization generally lasted from 2 to 7 days, but one case required a stay of 30 days. We found that the length of hospitalization was related to the severity of tissue necrosis.
One patient was found to have acute renal failure (ARF) during hospitalization. The delay between the bite and the onset of oliguria was 72 hours. Hemodi-alysis was then initiated, but respiratory failure de-veloped and intubation was performed. The patient received three hemodialysis treatments, and intubation time was 7 days. Another patient also received intu-bation for 3 days, due to acute pulmonary edema. Almost all victims showed some degree of tissue necro-sis at the bite site. Four victims required fasciotomy due to compartment syndrome, and three out of these four patients required more than one surgical debride-ment. Skin grafting was carried out in these three cases. In our series, there was no mortality due to venomous snake bites.
D
ISCUSSIONSnake bites in southern Taiwan are still a public health problem, although the number of victims has decreased due to rapid urbanization and the degra-dation of snake habitats. The incidence of snake bite is highest in rural areas, with farmers and visiting urban dwellers at greatest risk.
0 5 10 15 20 25 30 35
Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
F re q ue ncy (%) Jan
Taiwan is home to 37 species of snakes, a dozen of which are poisonous. The six most commonly-encountered indigenous venomous snakes in Taiwan (Figure 2) are the Taiwan cobra (Naja naja atra), the Taiwan banded krait (Bungarus multicinctus), Russell’s pit viper (Vipera russellii formosensis), the sharp-nosed pit viper (Deinagkistrodon acutus), the Taiwan Habu
(Trimeresurus mucrosquamatus), and the bamboo viper (Trimeresurus stejnegeri). Apart from their different appearances, there are some specific local symptoms of bite wound, as listed in Table 1.
The first step in treatment is triage first aid. Good first aid can be life-saving, but bad first aid still pre-dominates. Most of the once fashionable first aid
A B
D C
E F
Figure 2.The six most commonly encountered indigenous venomous snakes in Taiwan. (A) Taiwan cobra (Naja naja atra). (B) Taiwan banded krait (Bungarus multicinctus). (C) Russell’s pit viper (Vipera russellii formosensis). (D) Sharp-nosed pit viper (Deinagkistrodon acutus). (E) Taiwan Habu (Trimeresurus mucrosquamatus). (F) Bamboo viper (Trimeresurus stejnegeri).
methods, such as local incisions, suction, cryotherapy, potassium permanganate injections and electric shock have been proven to be of no value and have been abandoned. The two most important principles of first aid for snake bite are immobilization of the bitten limb and rapid transport to medical care. Immediately after a snake bite, the bite site should be immobilized to delay the spread of venom. Reassurance of the victim is also important.
The principles of medical care are identification of the species responsible for the bite, and close observa-tion of the victim, especially during the first 24–48 hours after the bite. Asymptomatic cases, with no local swelling after 2 hours, may be discharged. However, symptomatic cases should be monitored for a mini-mum of 24 hours. Hospital management of snake bite hinges on neutralization of the venom with adequate quantities of intravenous antivenin, plus supportive treatments. Antivenins are recommended to be injected intravenously, with a dosage of one vial. Another dose may be given if symptoms/signs show no improve-ment. Supportive modality (such as ventilatory equip-ment if the victim is paralyzed) can be crucial, as antivenin does not always reverse paralysis. However, antivenins [1] are the only specific antidote to enven-oming. A simple, rapid, whole blood clotting test has proven useful in many countries for diagnosis, both to indicate systemic envenoming requiring antivenin, and to control the dosage of antivenin. If the blood fails to coagulate by a standard time, a second dose of antivenin should be given and the test repeated at fixed intervals until coagulation has been restored. For com-plicated cases, close monitoring of blood and renal tests is necessary to prevent hemotoxic and renal complications.
Snake venoms are a mixture of complex toxins that may be independent, synergistic or antagonistic in
action. There are several classification systems, but the most medically useful system lists them in terms of their clinical effects. The major groups are neurotox-ins, myotoxneurotox-ins, coagulotoxins (hemotoxins), nephro-toxins and necronephro-toxins. In Taiwan, three venomous snakes, the sharp-nosed pit viper, the Taiwan Habu and the bamboo viper, produce hemotoxins. However, the Taiwan cobra and the Taiwan banded krait produce neurotoxins. Mixed toxins, combining hemotoxins and neurotoxins, are secreted by Russell’s pit viper. It is important to keep in mind that the actual mix of toxins in the venom of a given species of snake will vary by individual, age, and season. Furthermore, the quantity of venom injected in a bite can be highly variable.
The clinical manifestations of venomous snake bites vary from mild local reactions to severe, life-threatening systemic reactions. Bites from species causing local tissue injury commonly result in rapid development of local swelling, blistering, or bruising; the rapidity of development mirrors the severity of the bite. If systemic effects occur, they may be general, such as headache, nausea, vomiting, abdominal pain, diarrhea, collapse or convulsions; alternatively, they may be specific, such as ptosis or progressive weakness (neurotoxins), mus-cle pain, myoglobinuria (myotoxins), oozing of blood from wounds or gums, extensive bruising (coagulotox-ins), and oliguria or anuria (nephrotoxins). Death may occur early, usually because of shock or secondary myocardial effects of coagulotoxins, but is more usu-ally delayed and caused by inadequate treatment of paralysis, myolysis, coagulopathy, renal failure, or extensive tissue injury. Thus, death is often preventable in many cases. If a significant amount of venom has been injected, then local and/or systemic envenoming will almost inevitably follow; however, the rate of onset of systemic envenoming may be hastened by physical activity or slowed by effective first aid. Table 1.Local symptoms of bite wounds
Species of venomous snake Local symptoms
Taiwan cobra (Naja naja atra) Tooth marks appear shallow with slight bruising and trauma at the wound, which darkens quickly with ominous blistering
Taiwan banded krait (Bungarus multicinctus) Difficult to detect needle-like tooth marks
Russell’s pit viper (Vipera russellii formosensis) Pin-like bite marks appear as black dots, marked by swelling around the tooth marks
Sharp-nosed pit viper (Deinagkistrodon acutus) Blackened tooth marks become visible a few minutes after the bite Taiwan Habu (Trimeresurus mucrosquamatus) Visual pin-shaped tooth marks become imminently visible a few
minutes after been bitten
T
able 2.
Species and sites of snake bite, delay for antivenins and tr
eatment course Patient Age Sex Location Bite ar ea Snake Delay Fasciotomy Debridement Skin Intubation Hemodialysis Hospitalization no. (yr) species* interval (hr) graft (d) 1 45 F W orking Right foot B 7 ++ (2) † ++ 34 2 61 M Outdoor Left leg D 3 6 3 57 M Outdoor Right foramen A 6 6 4 59 M Indoor Right hand D 1 3 5 28 M Indoor Right thumb A 0.5 5 6 61 M Outdoor
Right dorsal foot
B 4 ++ 21 7 25 M Outdoor
Left middle finger
D 22 5 8 48 M Outdoor Left 4 th finger D 3 7 9 61 F Indoor
Right dorsal hand
A 6 ++ (2) † + 28 10 71 M Outdoor Right 3 rd toe B 6 5 11 52 M W orking
Left hand first
A 30 3 webspace 12 60 M W orking Left thumb D 1 4 13 20 M Catching
Left upper lip
B 13 3 14 30 M Indoor Left index B 2 4 15 39 M W orking
Right foot, dorsum
B 8 6 16 62 M Outdoor
Right dorsal foot
C 20 9 17 60 M W orking
Right index finger
A 2 ++ + 15 18 30 M Outdoor
Right dorsal foot
A 3 6 19 9 F Outdoor
Left dorsal foot
D 7 7 20 46 M Outdoor
Right middle finger
B 1 4 21 64 M Outdoor
Right lower leg
B 10 ++ 16 22 21 M W orking Left 4 th finger D 3 4 23 28 M Outdoor Left 5 th finger tip C 9 + 11 24 20 M Indoor Right foot D 17 7 25 51 F W orking Right upper D 2 4 extr emity 26 10 F Indoor Right hand C 1 5 27 20 F Indoor Right foot C 5 9 28 21 M Indoor
Right middle finger
B 1 6 29 74 F Outdoor Right thumb D 7 8 30 21 M Outdoor Right thumb B 4 7 31 27 M W orking
Right index finger
A 3 3 32 44 M W orking Right foot C 2 6 33 38 F Outdoor
Right lower leg
D 11 3 34 46 F Indoor
Left dorsal foot
A
1
9
*Snake species: T
aiwan cobra (A), Russell’s pit viper (B), T
aiwan Habu (C), and Bamboo viper (D);
†mor
In general, viper bites are often a significant cause of mortality in southern Taiwan because of their mixed toxins, and the severity of local and systemic reactions is usually greater than that of other species. However, hematologic changes caused by systemic envenoming, such as coagulopathy and hemolysis, are the most common pathologic manifestations [2,3]. ARF is the most common finding in cases of lethal envenomiza-tion, while coagulation abnormalities and shock are other key clinical features. ARF following snake bites has also been frequently reported [4,5]. Many investi-gators have shown that Russell’s viper venom may have both direct and indirect nephrotoxicity, which might cause multifactorial effects on renal tubular cells [6] and the renal vasculature [7]. In cases of direct nephrotoxicity, all of the proximal tubules of the kidney are affected evenly, with a preserved basement membrane. The indirect (ischemic) type of renal injury that is caused by severe renal tubular and cortical necrosis is highly correlated with disseminated intra-vascular coagulopathy. Experimentally, viper venom causes mesangiolysis, and this may be a significant factor in the pathogenesis of viper bite-induced glomerular disease. Treatment with antivenin is com-monly used. Dialysis and supportive treatment appear to be the mainstay of therapy in cases complicated by renal failure. In our study, only one victim bitten by Russell’s pit viper developed ARF, and this patient made a full recovery after several dialysis treatments.
Antivenins are the only antidote to envenoming; species-specific antivenins neutralize circulating venom and reverse systemic symptoms. Neutralization of the venom’s effect is sometimes difficult to assess, be-cause it does not immediately release venom bound to binding sites at neuromuscular junctions. Therefore, additional doses of antivenin might be required if neu-rotoxicity or shock persists, or recurs within a few hours of the initial dose.
The primary local effect of venom is edema, which may be delayed or occur within minutes, but which is almost always present within 2 hours. Although the bite site is usually painful, pain may be minimal or absent. Snake bite commonly results in other local tissue injuries, such as blistering and bruising, and the rapidity of development mirrors the severity of the bite. In our study, there were no statistically sig-nificant differences in the severity of tissue necrosis among patients who received medical attention soon after being bitten, and those who did so only after
a significant delay. A previous study showed that antivenin administration within 30 minutes of a bite did not prevent local tissue damage [8]. However, hos-pitalization was prolonged significantly for patients with local tissue necrosis and systemic complications. In our report, seven victims underwent surgical de-bridement for necrotic wounds due to snake bites. Although it varied depending on the amount of venom injected and the species of snake, the hospitalization times of these seven severely bitten victims was more than 10 days (Table 2). The more times that surgical debridements were required, the more necessary were longer hospitalizations.
In Taiwan, dawn and dusk are prime times for encounters with snakes. Many snakes tend to be noc-turnal, or they are at least more docile during day-light hours. When walking at dawn or dusk, walkers must be particularly careful to avoid snakes. Slow walkers often do not make enough noise to frighten snakes away, but do cause sufficient vibrations for the snakes to “hear” them coming. Therefore, hikers and outdoor walkers must be alert while walking during peak snake bite times. However, in our series, there were nine cases of snake bite occurring indoors, by snakes that had entered their victims’ homes.
It is not commonly known that not all snake bites are effective at injecting venom. Ineffective bites, or “dry bites”, can be common in some species, account-ing for more than 50% of bites. In many parts of the world, bites by nonvenomous snakes outnumber bites by venomous species, further reducing the chances of a severe, venomous bite.
Although the incidence of snake bites throughout Taiwan has decreased because of the reduction in the snake population as a result of hunting and degrada-tion of their habitat, it is worth keeping in mind the priority of acute management of snake bites.
R
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Russell’s viper venom. J Mich State Med Soc 1955;54: 801–4.
4. Chugh KS, Sakhuja V. Renal failure from snake bites. Int J Artif Organs 1980;3:319–21.
5. Chaiyabutr N, Sitprija V. Pathophysiological effects of Russell’s viper venom on renal function. J Nat Toxins 1999;8:351–8.
6. Sitprija V, Boonpucknavig V. The kidney in tropical snakebite. Clin Nephrol 1977;8:377–83.
7. Jimenez-Porras JM. Biochemistry of snake venom. Clin Toxicol 1970;3:389–431.
8. Homma M, Tu AT. Antivenin for the treatment of local tissue damage due to envenomation by Southeast Asian snakes. Ineffectiveness in the prevention of local tissue damage in mice after envenomation. Am J Trop Med Hyg 1970;19:880–4.
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